diff --git a/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.sgml b/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.sgml index 6cde4ef3a6..cd443d65b5 100644 --- a/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.sgml @@ -1,2717 +1,3357 @@ Advanced Networking Synopsis The following chapter will cover some of the more frequently used network services on UNIX systems. This, of course, will pertain to configuring said services on your FreeBSD system. Gateways and Routes Contributed by &a.gryphon;. 6 October 1995. For one machine to be able to find another, there must be a mechanism in place to describe how to get from one to the other. This is called Routing. A route is a defined pair of addresses: a destination and a gateway. The pair indicates that if you are trying to get to this destination, send along through this gateway. There are three types of destinations: individual hosts, subnets, and default. The default route is used if none of the other routes apply. We will talk a little bit more about default routes later on. There are also three types of gateways: individual hosts, interfaces (also called links), and ethernet hardware addresses. An example To illustrate different aspects of routing, we will use the following example which is the output of the command netstat -r: Destination Gateway Flags Refs Use Netif Expire default outside-gw UGSc 37 418 ppp0 localhost localhost UH 0 181 lo0 test0 0:e0:b5:36:cf:4f UHLW 5 63288 ed0 77 10.20.30.255 link#1 UHLW 1 2421 foobar.com link#1 UC 0 0 host1 0:e0:a8:37:8:1e UHLW 3 4601 lo0 host2 0:e0:a8:37:8:1e UHLW 0 5 lo0 => host2.foobar.com link#1 UC 0 0 224 link#1 UC 0 0 The first two lines specify the default route (which we will cover in the next section) and the localhost route. The interface (Netif column) that it specifies to use for localhost is lo0, also known as the loopback device. This says to keep all traffic for this destination internal, rather than sending it out over the LAN, since it will only end up back where it started anyway. The next thing that stands out are the 0:e0:... addresses. These are ethernet hardware addresses. FreeBSD will automatically identify any hosts (test0 in the example) on the local ethernet and add a route for that host, directly to it over the ethernet interface, ed0. There is also a timeout (Expire column) associated with this type of route, which is used if we fail to hear from the host in a specific amount of time. In this case the route will be automatically deleted. These hosts are identified using a mechanism known as RIP (Routing Information Protocol), which figures out routes to local hosts based upon a shortest path determination. FreeBSD will also add subnet routes for the local subnet (10.20.30.255 is the broadcast address for the subnet 10.20.30, and foobar.com is the domain name associated with that subnet). The designation link#1 refers to the first ethernet card in the machine. You will notice no additional interface is specified for those. Both of these groups (local network hosts and local subnets) have their routes automatically configured by a daemon called routed. If this is not run, then only routes which are statically defined (ie. entered explicitly) will exist. The host1 line refers to our host, which it knows by ethernet address. Since we are the sending host, FreeBSD knows to use the loopback interface (lo0) rather than sending it out over the ethernet interface. The two host2 lines are an example of what happens when we use an ifconfig alias (see the section of ethernet for reasons why we would do this). The => symbol after the lo0 interface says that not only are we using the loopback (since this is address also refers to the local host), but specifically it is an alias. Such routes only show up on the host that supports the alias; all other hosts on the local network will simply have a link#1 line for such. The final line (destination subnet 224) deals with MultiCasting, which will be covered in a another section. The other column that we should talk about are the Flags. Each route has different attributes that are described in the column. Below is a short table of some of these flags and their meanings: U Up: The route is active. H Host: The route destination is a single host. G Gateway: Send anything for this destination on to this remote system, which will figure out from there where to send it. S Static: This route was configured manually, not automatically generated by the system. C Clone: Generates a new route based upon this route for machines we connect to. This type of route is normally used for local networks. W WasCloned: Indicated a route that was auto-configured based upon a local area network (Clone) route. L Link: Route involves references to ethernet hardware. Default routes When the local system needs to make a connection to remote host, it checks the routing table to determine if a known path exists. If the remote host falls into a subnet that we know how to reach (Cloned routes), then the system checks to see if it can connect along that interface. If all known paths fail, the system has one last option: the default route. This route is a special type of gateway route (usually the only one present in the system), and is always marked with a c in the flags field. For hosts on a local area network, this gateway is set to whatever machine has a direct connection to the outside world (whether via PPP link, or your hardware device attached to a dedicated data line). If you are configuring the default route for a machine which itself is functioning as the gateway to the outside world, then the default route will be the gateway machine at your Internet Service Provider's (ISP) site. Let us look at an example of default routes. This is a common configuration: [Local2] <--ether--> [Local1] <--PPP--> [ISP-Serv] <--ether--> [T1-GW] The hosts Local1 and Local2 are at your site, with the formed being your PPP connection to your ISP's Terminal Server. Your ISP has a local network at their site, which has, among other things, the server where you connect and a hardware device (T1-GW) attached to the ISP's Internet feed. The default routes for each of your machines will be: host default gateway interface Local2 Local1 ethernet Local1 T1-GW PPP A common question is Why (or how) would we set the T1-GW to be the default gateway for Local1, rather than the ISP server it is connected to?. Remember, since the PPP interface is using an address on the ISP's local network for your side of the connection, routes for any other machines on the ISP's local network will be automatically generated. Hence, you will already know how to reach the T1-GW machine, so there is no need for the intermediate step of sending traffic to the ISP server. As a final note, it is common to use the address ...1 as the gateway address for your local network. So (using the same example), if your local class-C address space was 10.20.30 and your ISP was using 10.9.9 then the default routes would be: Local2 (10.20.30.2) --> Local1 (10.20.30.1) Local1 (10.20.30.1, 10.9.9.30) --> T1-GW (10.9.9.1) Dual homed hosts There is one other type of configuration that we should cover, and that is a host that sits on two different networks. Technically, any machine functioning as a gateway (in the example above, using a PPP connection) counts as a dual-homed host. But the term is really only used to refer to a machine that sits on two local-area networks. In one case, the machine as two ethernet cards, each having an address on the separate subnets. Alternately, the machine may only have one ethernet card, and be using ifconfig aliasing. The former is used if two physically separate ethernet networks are in use, the latter if there is one physical network segment, but two logically separate subnets. Either way, routing tables are set up so that each subnet knows that this machine is the defined gateway (inbound route) to the other subnet. This configuration, with the machine acting as a Bridge between the two subnets, is often used when we need to implement packet filtering or firewall security in either or both directions. Routing propagation We have already talked about how we define our routes to the outside world, but not about how the outside world finds us. We already know that routing tables can be set up so that all traffic for a particular address space (in our examples, a class-C subnet) can be sent to a particular host on that network, which will forward the packets inbound. When you get an address space assigned to your site, your service provider will set up their routing tables so that all traffic for your subnet will be sent down your PPP link to your site. But how do sites across the country know to send to your ISP? There is a system (much like the distributed DNS information) that keeps track of all assigned address-spaces, and defines their point of connection to the Internet Backbone. The Backbone are the main trunk lines that carry Internet traffic across the country, and around the world. Each backbone machine has a copy of a master set of tables, which direct traffic for a particular network to a specific backbone carrier, and from there down the chain of service providers until it reaches your network. It is the task of your service provider to advertise to the backbone sites that they are the point of connection (and thus the path inward) for your site. This is known as route propagation. Troubleshooting Sometimes, there is a problem with routing propagation, and some sites are unable to connect to you. Perhaps the most useful command for trying to figure out where a routing is breaking down is the &man.traceroute.8; command. It is equally useful if you cannot seem to make a connection to a remote machine (i.e. &man.ping.8; fails). The &man.traceroute.8; command is run with the name of the remote host you are trying to connect to. It will show the gateway hosts along the path of the attempt, eventually either reaching the target host, or terminating because of a lack of connection. For more information, see the manual page for &man.traceroute.8;. Bridging Written by Steve Peterson steve@zpfe.com. Introduction It is sometimes useful to divide one physical network (i.e., an Ethernet segment) into two separate network segments, without having to create IP subnets and use a router to connect the segments together. A device that connects two networks together in this fashion is called a bridge. and a FreeBSD system with two network interface cards can act as a bridge. The bridge works by learning the MAC layer addresses (i.e., Ethernet addresses) of the devices on each of its network interfaces. It forwards traffic between two networks only when its source and destination are on different networks. In many respects, a bridge is like an Ethernet switch with very few ports. Situations where bridging is appropriate There are two common situations in which a bridge is used today. High traffic on a segment Situation one is where your physical network segment is overloaded with traffic, but you don't want for whatever reason to subnet the network and interconnect the subnets with a router. Let's consider an example of a newspaper where the Editorial and Production departments are on the same subnetwork. The Editorial users all use server A for file service, and the Production users are on server B. An Ethernet is used to connect all users together, and high loads on the network are slowing things down. If the Editorial users could be segregated on one network segment and the Production users on another, the two network segments could be connected with a bridge. Only the network traffic destined for interfaces on the "other" side of the bridge would be sent to the other network, reducing congestion on each network segment. Filtering/traffic shaping firewall The second common situation is where firewall functionality is needed without IP Masquerading (NAT). An example is a small company that is connected via DSL or ISDN to their ISP. They have a 13 address global IP allocation for their ISP and have 10 PCs on their network. In this situation, using a router-based firewall is difficult because of subnetting issues. A bridge-based firewall can be configured and dropped into the path just downstream of their DSL/ISDN router without any IP numbering issues. Configuring a bridge Network interface card selection A bridge requires at least two network cards to function. Unfortunately, not all network interface cards as of FreeBSD 4.0 support bridging. Read &man.bridge.4; for details on the cards that are supported. Install and test the two network cards before continuing. Kernel configuration changes To enable kernel support for bridging, add the options BRIDGE statement to your kernel configuration file, and rebuild your kernel. Firewall support If you are planning to use the bridge as a firewall, you will need to add the IPFIREWALL option as well. Read for general information on configuring the bridge as a firewall. If you need to allow non-IP packets (such as ARP) to flow through the bridge, there is an undocumented firewall option that must be set. This option is IPFIREWALL_DEFAULT_TO_ACCEPT. Note that this changes the default rule for the firewall to accept any packet. Make sure you know how this changes the meaning of your ruleset before you set it. Traffic shaping support If you want to use the bridge as a traffic shaper, you will need to add the DUMMYNET option to your kernel configuration. Read &man.dummynet.4; for further information. Enabling the bridge Add the line net.link.ether.bridge=1 to /etc/sysctl.conf to enable the bridge at runtime. If you want the bridged packets to be filtered by ipfw, you should also add net.link.ether.bridge_ipfw=1 as well. Performance My bridge/firewall is a Pentium 90 with one 3Com 3C900B and one 3C905B. The protected side of the network runs at 10mbps half duplex and the connection between the bridge and my router (a Cisco 675) runs at 100mbps full duplex. With no filtering enabled, I've found that the bridge adds about 0.4 milliseconds of latency to pings from the protected 10mbps network to the Cisco 675. Other information If you want to be able to telnet into the bridge from the network, it is OK to assign one of the network cards an IP address. The consensus is that assigning both cards an address is a bad idea. If you have multiple bridges on your network, there cannot be more than one path between any two workstations. Technically, this means that there is no support for spanning tree link management. NFS Written by &a.unfurl;, 4 March 2000. Among the many different file systems that FreeBSD supports is a very unique type, the Network File System or NFS. NFS allows you to share directories and files on one machine with one or more other machines via the network they are attached to. Using NFS, users and programs can access files on remote systems as if they were local files. NFS has several benefits: Local workstations dont need as much disk space because commonly used data can be stored on a single machine and still remain accessible to everyone on the network. There is no need for users to have unique home directories on every machine on your network. Once they have an established directory that is available via NFS it can be accessed from anywhere. Storage devices such as floppies and CD-ROM drives can be used by other machines on the network eliminating the need for extra hardware. How It Works NFS is composed of two sides – a client side and a server side. Think of it as a want/have relationship. The client wants the data that the server side has. The server shares its data with the client. In order for this system to function properly a few processes have to be configured and running properly. The server has to be running the following daemons: nfsd - The NFS Daemon which services requests from NFS clients. mountd - The NFS Mount Daemon which actually carries out requests that nfsd passes on to it. portmap - The portmapper daemon which allows NFS clients to find out which port the NFS server is using. The client side only needs to run a single daemon: nfsiod - The NFS async I/O Daemon which services requests from its NFS server. Configuring NFS Luckily for us, on a FreeBSD system this setup is a snap. The processes that need to be running can all be run at boot time with a few modifications to your /etc/rc.conf file. On the NFS server make sure you have: portmap_enable="YES" nfs_server_enable="YES" nfs_server_flags="-u -t -n 4" mountd_flags="-r" mountd is automatically run whenever the NFS server is enabled. The and flags to nfsd tell it to serve UDP and TCP clients. The flag tells nfsd to start 4 copies of itself. On the client, make sure you have: nfs_client_enable="YES" nfs_client_flags="-n 4" Like nfsd, the tells nfsiod to start 4 copies of itself. The last configuration step requires that you create a file called /etc/exports. The exports file specifies which file systems on your server will be shared (a.k.a., exported) and with what clients they will be shared. Each line in the file specifies a file system to be shared. There are a handful of options that can be used in this file but I will only touch on a few of them. You can find out about the rest in the &man.exports.5; man page. Here are a few example /etc/exports entries: The following line exports /cdrom to three silly machines that have the same domain name as the server (hence the lack of a domain name for each) or have entries in your /etc/hosts file. The flag makes the shared file system read-only. With this flag, the remote system will not be able to make any changes to the the shared file system. /cdrom -ro moe larry curly The following line exports /home to three hosts by IP address. This is a useful setup if you have a private network but do not have DNS running. The flag allows all the directories below the specified file system to be exported as well. /home -alldirs 10.0.0.2 10.0.0.3 10.0.0.4 The following line exports /a to two machines that have different domain names than the server. The flag allows the root user on the remote system to write to the shared file system as root. Without the -maproot=0 flag even if someone has root access on the remote system they won't be able to modify files on the shared file system. /a -maproot=0 host.domain.com box.example.com In order for a client to share an exported file system it must have permission to do so. Make sure your client is listed in your /etc/exports file. Now that you have made all these changes you can just reboot and let FreeBSD start everything for you at boot time or you can run the following commands as root: On the NFS server: &prompt.root; portmap &prompt.root; nfsd -u -t -n 4 &prompt.root; mountd -r On the NFS client: &prompt.root; nfsiod -n 4 Now you should be ready to actually mount a remote file system. This can be done one of two ways. In these examples the server's name will be server and the client's name will be client. If you just want to temporarily mount a remote file system or just want to test out your config you can run a command like this as root on the client: &prompt.root; mount server:/home /mnt This will mount /home on the server on /mnt on the client. If everything is setup correctly you should be able to go into /mnt on the client and see all the files that are on the server. If you want to permanently (each time you reboot) mount a remote file system you need to add it to your /etc/fstab file. Here is an example line: server:/home /mnt nfs rw 0 0 Read the &man.fstab.5; man page for more options. Practical Uses There are many very cool uses for NFS. I use it quite a bit on the LAN I admin. Here are a few ways I have found it to be useful. I have several machines on my network but only one of them has a CD-ROM drive. Why? Because I have that one CD-ROM drive shared with all the others via NFS. The same can be done with floppy drives. With so many machines on the network it gets old having your personal files strewn all over the place. I have a central NFS server that houses all user home directories and shares them with the rest of the machines on the LAN, so no matter where I login I have the same home directory. When you get to reinstalling FreeBSD on one of your machines, NFS is the way to go. Just pop your distribution CD into your file server and away you go. I have a common /usr/ports/distfiles directory that all my machines share. That way when I go to install a port that I already installed on a different machine I do not have to download the source all over again. Problems integrating with other systems Contributed by &a.jlind;. Certain Ethernet adapters for ISA PC systems have limitations which can lead to serious network problems, particularly with NFS. This difficulty is not specific to FreeBSD, but FreeBSD systems are affected by it. The problem nearly always occurs when (FreeBSD) PC systems are networked with high-performance workstations, such as those made by Silicon Graphics, Inc., and Sun Microsystems, Inc. The NFS mount will work fine, and some operations may succeed, but suddenly the server will seem to become unresponsive to the client, even though requests to and from other systems continue to be processed. This happens to the client system, whether the client is the FreeBSD system or the workstation. On many systems, there is no way to shut down the client gracefully once this problem has manifested itself. The only solution is often to reset the client, because the NFS situation cannot be resolved. Though the correct solution is to get a higher performance and capacity Ethernet adapter for the FreeBSD system, there is a simple workaround that will allow satisfactory operation. If the FreeBSD system is the server, include the option on the mount from the client. If the FreeBSD system is the client, then mount the NFS file system with the option . These options may be specified using the fourth field of the fstab entry on the client for automatic mounts, or by using the parameter of the mount command for manual mounts. It should be noted that there is a different problem, sometimes mistaken for this one, when the NFS servers and clients are on different networks. If that is the case, make certain that your routers are routing the necessary UDP information, or you will not get anywhere, no matter what else you are doing. In the following examples, fastws is the host (interface) name of a high-performance workstation, and freebox is the host (interface) name of a FreeBSD system with a lower-performance Ethernet adapter. Also, /sharedfs will be the exported NFS filesystem (see man exports), and /project will be the mount point on the client for the exported file system. In all cases, note that additional options, such as or and may be desirable in your application. Examples for the FreeBSD system (freebox) as the client: in /etc/fstab on freebox: fastws:/sharedfs /project nfs rw,-r=1024 0 0 As a manual mount command on freebox: &prompt.root; mount -t nfs -o -r=1024 fastws:/sharedfs /project Examples for the FreeBSD system as the server: in /etc/fstab on fastws: freebox:/sharedfs /project nfs rw,-w=1024 0 0 As a manual mount command on fastws: &prompt.root; mount -t nfs -o -w=1024 freebox:/sharedfs /project Nearly any 16-bit Ethernet adapter will allow operation without the above restrictions on the read or write size. For anyone who cares, here is what happens when the failure occurs, which also explains why it is unrecoverable. NFS typically works with a block size of 8k (though it may do fragments of smaller sizes). Since the maximum Ethernet packet is around 1500 bytes, the NFS block gets split into multiple Ethernet packets, even though it is still a single unit to the upper-level code, and must be received, assembled, and acknowledged as a unit. The high-performance workstations can pump out the packets which comprise the NFS unit one right after the other, just as close together as the standard allows. On the smaller, lower capacity cards, the later packets overrun the earlier packets of the same unit before they can be transferred to the host and the unit as a whole cannot be reconstructed or acknowledged. As a result, the workstation will time out and try again, but it will try again with the entire 8K unit, and the process will be repeated, ad infinitum. By keeping the unit size below the Ethernet packet size limitation, we ensure that any complete Ethernet packet received can be acknowledged individually, avoiding the deadlock situation. Overruns may still occur when a high-performance workstations is slamming data out to a PC system, but with the better cards, such overruns are not guaranteed on NFS units. When an overrun occurs, the units affected will be retransmitted, and there will be a fair chance that they will be received, assembled, and acknowledged. Diskless Operation Contributed by &a.martin;. netboot.com/netboot.rom allow you to boot your FreeBSD machine over the network and run FreeBSD without having a disk on your client. Under 2.0 it is now possible to have local swap. Swapping over NFS is also still supported. Supported Ethernet cards include: Western Digital/SMC 8003, 8013, 8216 and compatibles; NE1000/NE2000 and compatibles (requires recompile) Setup Instructions Find a machine that will be your server. This machine will require enough disk space to hold the FreeBSD 2.0 binaries and have bootp, tftp and NFS services available. Tested machines: HP9000/8xx running HP-UX 9.04 or later (pre 9.04 doesn't work) Sun/Solaris 2.3. (you may need to get bootp) Set up a bootp server to provide the client with IP, gateway, netmask. diskless:\ :ht=ether:\ :ha=0000c01f848a:\ :sm=255.255.255.0:\ :hn:\ :ds=192.1.2.3:\ :ip=192.1.2.4:\ :gw=192.1.2.5:\ :vm=rfc1048: Set up a TFTP server (on same machine as bootp server) to provide booting information to client. The name of this file is cfg.X.X.X.X (or /tftpboot/cfg.X.X.X.X, it will try both) where X.X.X.X is the IP address of the client. The contents of this file can be any valid netboot commands. Under 2.0, netboot has the following commands: help print help list ip print/set client's IP address server print/set bootp/tftp server address netmask print/set netmask hostname name print/set hostname kernel print/set kernel name rootfs print/set root filesystem swapfs print/set swap filesystem swapsize set diskless swapsize in KBytes diskboot boot from disk autoboot continue boot process trans | turn transceiver on|off flags set boot flags A typical completely diskless cfg file might contain: rootfs 192.1.2.3:/rootfs/myclient swapfs 192.1.2.3:/swapfs swapsize 20000 hostname myclient.mydomain A cfg file for a machine with local swap might contain: rootfs 192.1.2.3:/rootfs/myclient hostname myclient.mydomain Ensure that your NFS server has exported the root (and swap if applicable) filesystems to your client, and that the client has root access to these filesystems A typical /etc/exports file on FreeBSD might look like: /rootfs/myclient -maproot=0:0 myclient.mydomain /swapfs -maproot=0:0 myclient.mydomain And on HP-UX: /rootfs/myclient -root=myclient.mydomain /swapfs -root=myclient.mydomain If you are swapping over NFS (completely diskless configuration) create a swap file for your client using dd. If your swapfs command has the arguments /swapfs and the size 20000 as in the example above, the swapfile for myclient will be called /swapfs/swap.X.X.X.X where X.X.X.X is the client's IP addr, e.g.: &prompt.root; dd if=/dev/zero of=/swapfs/swap.192.1.2.4 bs=1k count=20000 Also, the client's swap space might contain sensitive information once swapping starts, so make sure to restrict read and write access to this file to prevent unauthorized access: &prompt.root; chmod 0600 /swapfs/swap.192.1.2.4 Unpack the root filesystem in the directory the client will use for its root filesystem (/rootfs/myclient in the example above). On HP-UX systems: The server should be running HP-UX 9.04 or later for HP9000/800 series machines. Prior versions do not allow the creation of device files over NFS. When extracting /dev in /rootfs/myclient, beware that some systems (HPUX) will not create device files that FreeBSD is happy with. You may have to go to single user mode on the first bootup (press control-c during the bootup phase), cd /dev and do a sh ./MAKEDEV all from the client to fix this. Run netboot.com on the client or make an EPROM from the netboot.rom file Using Shared <filename>/</filename> and <filename>/usr</filename> filesystems At present there isn't an officially sanctioned way of doing this, although I have been using a shared /usr filesystem and individual / filesystems for each client. If anyone has any suggestions on how to do this cleanly, please let me and/or the &a.core; know. Compiling netboot for specific setups Netboot can be compiled to support NE1000/2000 cards by changing the configuration in /sys/i386/boot/netboot/Makefile. See the comments at the top of this file. ISDN Last modified by &a.wlloyd;. A good resource for information on ISDN technology and hardware is Dan Kegel's ISDN Page. A quick simple road map to ISDN follows: If you live in Europe I suggest you investigate the ISDN card section. If you are planning to use ISDN primarily to connect to the Internet with an Internet Provider on a dial-up non-dedicated basis, I suggest you look into Terminal Adapters. This will give you the most flexibility, with the fewest problems, if you change providers. If you are connecting two LANs together, or connecting to the Internet with a dedicated ISDN connection, I suggest you consider the stand alone router/bridge option. Cost is a significant factor in determining what solution you will choose. The following options are listed from least expensive to most expensive. ISDN Cards Contributed by &a.hm;. This section is really only relevant to ISDN users in countries where the DSS1/Q.931 ISDN standard is supported. Some growing number of PC ISDN cards are supported under FreeBSD 2.2.x and up by the isdn4bsd driver package. It is still under development but the reports show that it is successfully used all over Europe. The latest isdn4bsd version is available from ftp://isdn4bsd@ftp.consol.de/pub/, the main isdn4bsd ftp site (you have to log in as user isdn4bsd , give your mail address as the password and change to the pub directory. Anonymous ftp as user ftp or anonymous will not give the desired result). Isdn4bsd allows you to connect to other ISDN routers using either IP over raw HDLC or by using synchronous PPP. A telephone answering machine application is also available. Many ISDN PC cards are supported, mostly the ones with a Siemens ISDN chipset (ISAC/HSCX), support for other chipsets (from Motorola, Cologne Chip Designs) is currently under development. For an up-to-date list of supported cards, please have a look at the README file. In case you are interested in adding support for a different ISDN protocol, a currently unsupported ISDN PC card or otherwise enhancing isdn4bsd, please get in touch with hm@kts.org. A majordomo maintained mailing list is available. To join the list, send mail to &a.majordomo; and specify: subscribe freebsd-isdn in the body of your message. ISDN Terminal Adapters Terminal adapters(TA), are to ISDN what modems are to regular phone lines. Most TA's use the standard hayes modem AT command set, and can be used as a drop in replacement for a modem. A TA will operate basically the same as a modem except connection and throughput speeds will be much faster than your old modem. You will need to configure PPP exactly the same as for a modem setup. Make sure you set your serial speed as high as possible. The main advantage of using a TA to connect to an Internet Provider is that you can do Dynamic PPP. As IP address space becomes more and more scarce, most providers are not willing to provide you with a static IP anymore. Most stand-alone routers are not able to accommodate dynamic IP allocation. TA's completely rely on the PPP daemon that you are running for their features and stability of connection. This allows you to upgrade easily from using a modem to ISDN on a FreeBSD machine, if you already have PPP setup. However, at the same time any problems you experienced with the PPP program and are going to persist. If you want maximum stability, use the kernel PPP option, not the user-land iijPPP. The following TA's are know to work with FreeBSD. Motorola BitSurfer and Bitsurfer Pro Adtran Most other TA's will probably work as well, TA vendors try to make sure their product can accept most of the standard modem AT command set. The real problem with external TA's is like modems you need a good serial card in your computer. You should read the serial ports section in the handbook for a detailed understanding of serial devices, and the differences between asynchronous and synchronous serial ports. A TA running off a standard PC serial port (asynchronous) limits you to 115.2Kbs, even though you have a 128Kbs connection. To fully utilize the 128Kbs that ISDN is capable of, you must move the TA to a synchronous serial card. Do not be fooled into buying an internal TA and thinking you have avoided the synchronous/asynchronous issue. Internal TA's simply have a standard PC serial port chip built into them. All this will do, is save you having to buy another serial cable, and find another empty electrical socket. A synchronous card with a TA is at least as fast as a stand-alone router, and with a simple 386 FreeBSD box driving it, probably more flexible. The choice of sync/TA v.s. stand-alone router is largely a religious issue. There has been some discussion of this in the mailing lists. I suggest you search the archives for the complete discussion. Stand-alone ISDN Bridges/Routers ISDN bridges or routers are not at all specific to FreeBSD or any other operating system. For a more complete description of routing and bridging technology, please refer to a Networking reference book. In the context of this page, I will use router and bridge interchangeably. As the cost of low end ISDN routers/bridges comes down, it will likely become a more and more popular choice. An ISDN router is a small box that plugs directly into your local Ethernet network(or card), and manages its own connection to the other bridge/router. It has all the software to do PPP and other protocols built in. A router will allow you much faster throughput that a standard TA, since it will be using a full synchronous ISDN connection. The main problem with ISDN routers and bridges is that interoperability between manufacturers can still be a problem. If you are planning to connect to an Internet provider, I recommend that you discuss your needs with them. If you are planning to connect two lan segments together, ie: home lan to the office lan, this is the simplest lowest maintenance solution. Since you are buying the equipment for both sides of the connection you can be assured that the link will work. For example to connect a home computer or branch office network to a head office network the following setup could be used. Branch office or Home network Network is 10 Base T Ethernet. Connect router to network cable with AUI/10BT transceiver, if necessary. ---Sun workstation | ---FreeBSD box | ---Windows 95 (Do not admit to owning it) | Stand-alone router | ISDN BRI line If your home/branch office is only one computer you can use a twisted pair crossover cable to connect to the stand-alone router directly. Head office or other lan Network is Twisted Pair Ethernet. -------Novell Server | H | | ---Sun | | | U ---FreeBSD | | | ---Windows 95 | B | |___---Stand-alone router | ISDN BRI line One large advantage of most routers/bridges is that they allow you to have 2 separate independent PPP connections to 2 separate sites at the same time. This is not supported on most TA's, except for specific(expensive) models that have two serial ports. Do not confuse this with channel bonding, MPP etc. This can be very useful feature, for example if you have an dedicated ISDN connection at your office and would like to tap into it, but don't want to get another ISDN line at work. A router at the office location can manage a dedicated B channel connection (64Kbs) to the internet, as well as a use the other B channel for a separate data connection. The second B channel can be used for dial-in, dial-out or dynamically bond(MPP etc.) with the first B channel for more bandwidth. An Ethernet bridge will also allow you to transmit more than just IP traffic, you can also send IPX/SPX or whatever other protocols you use. NIS/YP Written by &a.unfurl;, 21 January 2000, enhanced with parts and comments from Eric Ogren eogren@earthlink.net and Udo Erdelhoff ue@nathan.ruhr.de in June 2000. What is it? NIS, which stands for Network Information Services, was developed by Sun Microsystems to centralize administration of Unix (originally SunOS) systems. It has now essentially become an industry standard; all major Unices (Solaris, HP-UX, AIX, Linux, NetBSD, OpenBSD, FreeBSD, etc) support NIS. NIS was formerly known as Yellow Pages (or yp), but due to copyright violations, Sun was forced to change the name. It is a RPC-based client/server system that allows a group of machines within an NIS domain to share a common set of configuration files. This permits a system administrator to set up NIS client systems with only minimal configuration data and add, remove or modify configuration data from a single location. It is similar to Windows NT's domain system; although the internal implementation of the two aren't at all similar, the basic functionality can be compared. Terms/processes you should know There are several terms and several important user processes that you will come across when attempting to implement NIS on FreeBSD, whether you are trying to create an NIS server or act an NIS client: The NIS domainname. An NIS master server and all of its clients (including its slave servers) have a NIS domainname. Similar to an NT domain name, the NIS domainname does not have anything to do with DNS. portmap. portmap must be running in order to enable RPC (Remote Procedure Call, a network protocol used by NIS). If portmap is not running, it will be impossible to run an NIS server, or to act as an NIS client. ypbind. ypbind “binds” an NIS client to its NIS server. It will take the NIS domainname from the system, and using RPC, connect to the server. ypbind is the core of client-server communication in an NIS environment; if ypbind dies on a client machine, it will not be able to access the NIS server. ypserv. ypserv, which should only be running on NIS servers, is the NIS server process itself. If ypserv dies, then the server will no longer be able to respond to NIS requests (hopefully, there is a slave server to take over for it). There are some implementations of NIS (but not the FreeBSD one), that don't try to reconnect to another server if the server it used before dies. Often, the only thing that helps in this case is to restart the server process (or even the whole server) or the ypbind process on the client. rpc.yppasswdd. rpc.yppasswdd, another process that should only be running on NIS master servers, is a daemon that will allow NIS clients to change their NIS passwords. If this daemon is not running, users will have to login to the NIS master server and change their passwords there. How does it work? There are three types of hosts in an NIS environment; master servers, slave servers, and clients. Servers act as a central repository for host configuration information. Master servers hold the authoritative copy of this information, while slave servers mirror this information for redundancy. Clients rely on the servers to provide this information to them. Information in many files can be shared in this manner. The master.passwd, group, and hosts files are commonly shared via NIS. Whenever a process on a client needs information that would normally be found in these files locally, it makes a query to the server it is bound to, to get this information. Machine types A NIS master server. This server, analogous to a Windows NT primary domain controller, maintains the files used by all of the NIS clients. The passwd, group, and other various files used by the NIS clients live on the master server. It is possible for one machine to be an NIS master server for more than one NIS domain. However, this will not be covered in this introduction, which assumes a relatively small-scale NIS environment. NIS slave servers. Similar to NT's backup domain controllers, NIS slave servers maintain copies of the NIS master's data files. NIS slave servers provide the redundancy, which is needed in important environments. They also help to balance the load of the master server: NIS Clients always attach to the NIS server, whose response they get first, and this includes slave-server-replies. NIS clients. NIS clients, like most NT workstations, authenticate against the NIS server (or the NT domain controller in the NT Workstation case) to log on. Using NIS/YP This section will deal with setting up a sample NIS environment. This section assumes that you are running FreeBSD 3.3 or later. The instructions given here will probably work for any version of FreeBSD greater than 3.0, but there are no guarantees that this is true. Planning Let's assume that you are the administrator of a small university lab. This lab, which consists of 15 FreeBSD machines, currently has no centralized point of administration; each machine has its own /etc/passwd and /etc/master.passwd. These files are kept in sync with each other only through manual intervention; currently, when you add a user to the lab, you must run adduser on all 15 machines. Clearly, this has to change, so you have decided to convert the lab to use NIS, using two of the machines as servers. Therefore, the configuration of the lab now looks something like: Machine name IP address Machine role ellington 10.0.0.2 NIS master coltrane 10.0.0.3 NIS slave basie 10.0.0.4 Faculty workstation bird 10.0.0.5 Client machine cli[1-11] 10.0.0.[6-17] Other client machines If you are setting up a NIS scheme for the first time, it is a good idea to think through how you want to go about it. No matter what the size of your network, there are a few decisions that need to be made. Choosing a NIS Domain Name This might not be the domainname that you are used to. It is more accurately called the NIS domainname. When a client broadcasts its requests for info, it includes the name of the NIS domain that it is part of. This is how multiple servers on one network can tell which server should answer which request. Think of the NIS domainname as the name for a group of hosts that are related in someway way. Some organizations choose to use their Internet domainname for their NIS domainname. This is not recommended as it can cause confusion when trying to debug network problems. The NIS domainname should be unique within your network and it is helpful if it describes the group of machines it represents. For example, the Art department at Acme Inc. might be in the "acme-art" NIS domain. For this example, assume you have chosen the name test-domain. However, some operating systems (notably SunOS) use their NIS domain name as their Internet domain name. If one or more machines on your network have this restriction, you must use the Internet domain name as your NIS domain name. Physical Server Requirements There are several things to keep in mind when choosing a machine to use as a NIS server. One of the unfortunate things about NIS is the level of dependency the clients have on the server. If a client cannot contact the server for its NIS domain, very often the machine becomes unusable. The lack of user and group information causes most systems to temporarily freeze up. With this in mind you should make sure to choose a machine that won't be prone to being rebooted regularly, or one that might be used for development. The NIS server should ideally be a stand alone machine whose sole purpose in life is to be an NIS server. If you have a network that is not very heavily used, it is acceptable to put the NIS server on a machine running other services, just keep in mind that if the NIS server becomes unavailable, it will affect all of your NIS clients adversely. NIS Servers The canonical copies of all NIS information are stored on a single machine called the NIS master server. The databases used to store the information are called NIS maps. In FreeBSD, these maps are stored in /var/yp/[domainname] where [domainname] is the name of the NIS domain being served. A single NIS server can support several domains at once, therefore it is possible to have several such directories, one for each supported domain. Each domain will have its own independent set of maps. NIS master and slave servers handle all NIS requests with the ypserv daemon. Ypserv is responsible for receiving incoming requests from NIS clients, translating the requested domain and map name to a path to the corresponding database file and transmitting data from the database back to the client. Setting up a NIS master server Setting up a master NIS server can be relatively straight forward, depending on your needs. FreeBSD comes with support for NIS out-of-the-box. All you need is to add the following lines to /etc/rc.conf, and FreeBSD will do the rest for you. nisdomainname="test-domain" This line will set the NIS domainname to test-domain upon network setup (e.g. after reboot). nis_server_enable="YES" This will tell FreeBSD to start up the NIS server processes when the networking is next brought up. nis_yppasswdd_enable="YES" This will enable the rpc.yppasswdd daemon, which, as mentioned above, will allow users to change their NIS password from a client machine. Now, everything you have to do is to run the command /etc/netstart as superuser. It will setup everything for you, using the values you defined in /etc/rc.conf. Initializing the NIS maps The NIS maps are database files, that are kept in the /var/yp directory. They are generated from configuration files in the /etc directory of the NIS master, with one exception: the /etc/master.passwd file. This is for a good reason; you don't want to propagate passwords to your root and other administrative accounts to all the servers in the NIS domain. Therefore, before we initialize the NIS maps, you should: &prompt.root; cp /etc/master.passwd /var/yp/master.passwd &prompt.root; cd /var/yp &prompt.root; vi master.passwd You should remove all entries regarding system accounts (bin, tty, kmem, games, etc), as well as any accounts that you don't want to be propagated to the NIS clients (for example root and any other UID 0 (superuser) accounts). Make sure the /var/yp/master.passwd is neither group nor world readable (mode 600)! Use the chmod command, if appropriate. When you have finished, it's time to initialize the NIS maps! FreeBSD includes a script named ypinit to do this for you (see its man page for more information). Note that this script is available on most UNIX OSs, but not on all. On Digital Unix/Compaq Tru64 Unix it is called ypsetup. Because we are generating maps for an NIS master, we are going to pass the option to ypinit. To generate the NIS maps, assuming you already performed the steps above, run: ellington&prompt.root; ypinit -m test-domain Server Type: MASTER Domain: test-domain Creating an YP server will require that you answer a few questions. Questions will all be asked at the beginning of the procedure. Do you want this procedure to quit on non-fatal errors? [y/n: n] n Ok, please remember to go back and redo manually whatever fails. If you don't, something might not work. At this point, we have to construct a list of this domains YP servers. rod.darktech.org is already known as master server. Please continue to add any slave servers, one per line. When you are done with the list, type a <control D>. master server : ellington next host to add: coltrane next host to add: ^D The current list of NIS servers looks like this: ellington coltrane Is this correct? [y/n: y] y [..output from map generation..] NIS Map update completed. ellington has been setup as an YP master server without any errors. ypinit should have created /var/yp/Makefile from /var/yp/Makefile.dist. When created, this file assumes that you are operating in a single server NIS environment with only FreeBSD machines. Since test-domain has a slave server as well, you must edit /var/yp/Makefile: ellington&prompt.root; vi /var/yp/Makefile You should comment out the line that says `NOPUSH = "True"' (if it is not commented out already). Setting up a NIS slave server Setting up an NIS slave server is even more simple than setting up the master. Log on to the slave server and edit the file /etc/rc.conf as you did before. The only difference is that we now must use the option when running ypinit. The option requires the name of the NIS master be passed to it as well, so our command line looks like: coltrane&prompt.root; ypinit -s ellington test-domain Server Type: SLAVE Domain: test-domain Master: ellington Creating an YP server will require that you answer a few questions. Questions will all be asked at the beginning of the procedure. Do you want this procedure to quit on non-fatal errors? [y/n: n] n Ok, please remember to go back and redo manually whatever fails. If you don't, something might not work. There will be no further questions. The remainder of the procedure should take a few minutes, to copy the databases from ellington. Transferring netgroup... ypxfr: Exiting: Map successfully transferred Transferring netgroup.byuser... ypxfr: Exiting: Map successfully transferred Transferring netgroup.byhost... ypxfr: Exiting: Map successfully transferred Transferring master.passwd.byuid... ypxfr: Exiting: Map successfully transferred Transferring passwd.byuid... ypxfr: Exiting: Map successfully transferred Transferring passwd.byname... ypxfr: Exiting: Map successfully transferred Transferring group.bygid... ypxfr: Exiting: Map successfully transferred Transferring group.byname... ypxfr: Exiting: Map successfully transferred Transferring services.byname... ypxfr: Exiting: Map successfully transferred Transferring rpc.bynumber... ypxfr: Exiting: Map successfully transferred Transferring rpc.byname... ypxfr: Exiting: Map successfully transferred Transferring protocols.byname... ypxfr: Exiting: Map successfully transferred Transferring master.passwd.byname... ypxfr: Exiting: Map successfully transferred Transferring networks.byname... ypxfr: Exiting: Map successfully transferred Transferring networks.byaddr... ypxfr: Exiting: Map successfully transferred Transferring netid.byname... ypxfr: Exiting: Map successfully transferred Transferring hosts.byaddr... ypxfr: Exiting: Map successfully transferred Transferring protocols.bynumber... ypxfr: Exiting: Map successfully transferred Transferring ypservers... ypxfr: Exiting: Map successfully transferred Transferring hosts.byname... ypxfr: Exiting: Map successfully transferred coltrane has been setup as an YP slave server without any errors. Don't forget to update map ypservers on ellington. You should now have a directory called /var/yp/test-domain. Copies of the NIS master server's maps should be in this directory. You will need to make sure that these stay updated. The following /etc/crontab entries on your slave servers should do the job: 20 * * * * root /usr/libexec/ypxfr passwd.byname 21 * * * * root /usr/libexec/ypxfr passwd.byuid These two lines force the slave to sync its maps with the maps on the master server. Although this is not mandatory, because the master server tries to make sure any changes to it's NIS maps are communicated to it's slaves, the password information is so vital to systems that depend on the server, that it is a good idea to force the updates. This is more important on busy networks where map updates might not always complete. Now, run the command /etc/netstart on the slave server as well, which again starts the NIS server. NIS Clients An NIS client establishes what is called a binding to a particular NIS server using the ypbind daemon. ypbind checks the system's default domain (as set by the domainname command), and begins broadcasting RPC requests on the local network. These requests specify the name of the domain for which ypbind is attempting to establish a binding. If a server that has been configured to serve the requested domain receives one of the broadcasts, it will respond to ypbind, which will record the server's address. If there are several servers available (a master and several slaves, for example), ypbind will use the address of the first one to respond. From that point on, the client system will direct all of its NIS requests to that server. Ypbind will occasionally ping the server to make sure it is still up and running. If it fails to receive a reply to one of its pings within a reasonable amount of time, ypbind will mark the domain as unbound and begin broadcasting again in the hopes of locating another server. Setting up an NIS client Setting up a FreeBSD machine to be a NIS client is fairly straight forward. Edit the file /etc/rc.conf and add the following lines in order to set the NIS domainname and start ypbind upon network startup: nisdomainname="test-domain" nis_client_enable="YES" To import all possible password entries from the NIS server, add this line to your /etc/master.passwd file, using vipw: +::::::::: This line will afford anyone with a valid account in the NIS server's password maps an account. There are many ways to configure your NIS client by changing this line. See the netgroups part below for more information. For more detailed reading see O'Reilly's book on Managing NFS and NIS. To import all possible group entries from the NIS server, add this line to your /etc/group file: +:*:: After completing these steps, you should be able to run ypcat passwd and see the NIS server's passwd map. NIS Security In general, any remote user can issue an RPC to ypserv and retrieve the contents of your NIS maps, provided the remote user knows your domainname. To prevent such unauthorized transactions, ypserv supports a feature called securenets which can be used to restrict access to a given set of hosts. At startup, ypserv will attempt to load the securenets information from a file called /var/yp/securenets. This path varies depending on the path specified with the option. This file contains entries that consist of a network specification and a network mask separated by white space. Lines starting with # are considered to be comments. A sample securenets file might look like this: # allow connections from local host -- mandatory 127.0.0.1 255.255.255.255 # allow connections from any host # on the 192.168.128.0 network 192.168.128.0 255.255.255.0 # allow connections from any host # between 10.0.0.0 to 10.0.15.255 # this includes the machines in the testlab 10.0.0.0 255.255.240.0 If ypserv receives a request from an address that matches one of these rules, it will process the request normally. If the address fails to match a rule, the request will be ignored and a warning message will be logged. If the /var/yp/securenets file does not exist, ypserv will allow connections from any host. The ypserv program also has support for Wietse Venema's tcpwrapper package. This allows the administrator to use the tcpwrapper configuration files for access control instead of /var/yp/securenets. While both of these access control mechanisms provide some security, they, like the privileged port test, are vulnerable to IP spoofing attacks. All NIS-related traffic should be blocked at your firewall. Servers using /var/yp/securenets may fail to serve legitimate NIS clients with archaic TCP/IP implementations. Some of these implementations set all host bits to zero when doing broadcasts and/or fail to observe the subnet mask when calculating the broadcast address. While some of these problems can be fixed by changing the client configuration, other problems may force the retirement of the client systems in question or the abandonment of /var/yp/securenets. Using /var/yp/securenets on a server with such an archaic implementation of TCP/IP is a really bad idea and will lead to loss of NIS functionality for large parts of your network. The use of the tcpwrapper package increases the latency of your NIS server. The additional delay may be long enough to cause timeouts in client programs, especially in busy networks or with slow NIS servers. If one or more of your client systems suffers from these symptoms, you should convert the client systems in question into NIS slave servers and force them to bind to themselves. Barring some users from logging on In our lab, there is a machine basie that is supposed to be a faculty only workstation. We don't want to take this machine out of the NIS domain, yet the passwd file on the master NIS server contains accounts for both faculty and students. What can we do? There is a way to bar specific users from logging on to a machine, even if they are present in the NIS database. To do this, all you must do is add -username to the end of the /etc/master.passwd file on the client machine, where username is the username of the user you wish to bar from logging in. This should preferably be done using vipw, since vipw will sanity check your changes to /etc/master.passwd, as well as automatically rebuild the password database when you finish editing. For example, if we wanted to bar user bill from logging on to basie we would: basie&prompt.root; vipw [add -bill to the end, exit] vipw: rebuilding the database... vipw: done basie&prompt.root; cat /etc/master.passwd root:[password]:0:0::0:0:The super-user:/root:/bin/csh toor:[password]:0:0::0:0:The other super-user:/root:/bin/sh daemon:*:1:1::0:0:Owner of many system processes:/root:/sbin/nologin operator:*:2:5::0:0:System &:/:/sbin/nologin bin:*:3:7::0:0:Binaries Commands and Source,,,:/:/sbin/nologin tty:*:4:65533::0:0:Tty Sandbox:/:/sbin/nologin kmem:*:5:65533::0:0:KMem Sandbox:/:/sbin/nologin games:*:7:13::0:0:Games pseudo-user:/usr/games:/sbin/nologin news:*:8:8::0:0:News Subsystem:/:/sbin/nologin man:*:9:9::0:0:Mister Man Pages:/usr/share/man:/sbin/nologin bind:*:53:53::0:0:Bind Sandbox:/:/sbin/nologin uucp:*:66:66::0:0:UUCP pseudo-user:/var/spool/uucppublic:/usr/libexec/uucp/uucico xten:*:67:67::0:0:X-10 daemon:/usr/local/xten:/sbin/nologin pop:*:68:6::0:0:Post Office Owner:/nonexistent:/sbin/nologin nobody:*:65534:65534::0:0:Unprivileged user:/nonexistent:/sbin/nologin +::::::::: -bill basie&prompt.root; Using netgroups The netgroups part was contributed by Udo Erdelhoff ue@nathan.ruhr.de in July 2000. The method shown in the previous chapter works reasonably well if you need special rules for a very small number of users and/or machines. On larger networks, you will forget to bar some users from logging onto sensitive machines, or you may even have to modify each machine separately, thus loosing the main benefit of NIS, centralized administration. The NIS developers' solution for this problem is called netgroups. Their purpose and semantics can be compared to the normal groups used by Unix file systems. The main differences are the lack of a numeric id and the ability to define a netgroup by including both user accounts and other netgroups. Netgroups were developed to handle large, complex networks with hundreds of users and machines. On one hand, this is a Good Thing if you are forced to deal with such a situation. On the other hand, this complexity makes it almost impossible to explain netgroups with really simple examples. The example used in the remainder of this chapter demonstrates this problem. Let us assume that your successful introduction of NIS in your laboratory caught your superiors' interest. Your next job is to extend your NIS domain to cover some of the other machines on campus. The two tables contain the names of the new users and new machines as well as brief descriptions of them. User Name(s) Description alpha, beta Normal employees of the IT department charlie, delta The new apprentices of the IT department echo, foxtrott, golf, ... Ordinary employees able, baker, ... The current interns Machine Name(s) Description war, death, famine, pollution Your most important servers. Only the IT employees are allowed to log onto these machines. pride, greed, envy, wraith, lust, sloth Less important servers. All members of the IT department are allowed to login onto these machines. one, two, three, four, ... Ordinary workstations. Only the real employees are allowed to use these machines. trashcan A very old machine without any critical data. Even the intern is allowed to use this box. If you tried to implement these restrictions by separately blocking each user, you would have to add one -user line to each system's passwd for each user who is not allowed to login onto that system. If you forget just one entry, you could be in trouble. It may feasible to do this correctly during the initial setup, however you will eventually forget to add the lines for new users during day-to-day operations. After all, Murphy was an optimist. Handling this situation with netgroups offers several advantages. Each user need not be handled separately; you assign a user to one or netgroup and allow or forbid logins for all members of the netgroup. If you add a new machine, you will only have to define login restrictions for netgroups. If a new user is added, you will only have to add the user to one or more netgroups. Those changes are independent of each other; no more for each combination of user and machine do... If your NIS setup is planned carefully, you will only have to modify exactly one central configuration file to grant or deny access to machines. The first step is the initialization of the NIS map netgroup. FreeBSD's ypinit does not create this map by default, but its NIS implementation will support it once it has been created. To create an empty map, simply type ellington&prompt.root; vi /var/yp/netgroup and start adding content. For our example, we need at least four netgroups: IT employees, IT apprentices, normal employees and interns. IT_EMP (,alpha,test-domain) (,beta,test-domain) IT_APP (,charlie,test-domain) (,delta,test-domain) USERS (,echo,test-domain) (,foxtrott,test-domain) \ (,golf,test-domain) INTERNS (,able,test-domain) (,baker,test-domain) IT_EMP, IT_APP etc. are the names of the netgroups. Each bracketed group adds one or more user accounts to it. The three fields inside a group are: The name of the host(s) where the following items are valid. If you do not specify a hostname, the entry is valid on all hosts. If you do specify a hostname, you will a realm of darkness, horror and utter confusion. The name of the account that belongs to this netgroup. The NIS domain for the account. You can import accounts from other NIS domains into your netgroup if you are one of unlucky fellows with more than one NIS domain. Each of these fields can contain wildcards. See &man.netgroup.5; for details. Netgroup names longer than 8 characters should not be used, especially if you have machines running other operating systems within your NIS domain. The names are case sensitive; using capital letters for your netgroup names is an easy way to distinguish between user, machine and netgroup names. Some NIS clients (other than FreeBSD) cannot handle netgroups with a large number of entries. For example, some older versions of SunOS start to cause trouble if a netgroup contains more than 15 entries. You can circumvent this limit by creating several sub-netgroups with 15 users or less and a real netgroup that consists of the sub-netgroups: BIGGRP1 (,joe1,domain) (,joe2,domain) (,joe3,domain) [...] BIGGRP2 (,joe16,domain) (,joe17,domain) [...] BIGGRP3 (,joe32,domain) (,joe33,domain) BIGGROUP BIGGRP1 BIGGRP2 BIGGRP3 You can repeat this process if you need more than 225 users within a single netgroup. Activating and distributing your new NIS map is easy: ellington&prompt.root; cd /var/yp ellington&prompt.root; make This will generate the three NIS maps netgroup, netgroup.byhost and netgroup.byuser. Use &man.ypcat.1; to check if your new NIS map are available: ellington&prompt.user; ypcat -k netgroup ellington&prompt.user; ypcat -k netgroup.byhost ellington&prompt.user; ypcat -k netgroup.byuser The output of the first command should resemble the contents of /var/yp/netgroup. The second command will not produce output if you have not specified host-specific netgroups. The third command can be used to get the list of netgroups for a user. The client setup is quite simple. To configure the server war, you only have to start &man.vipw.8; and replace the line +::::::::: with +@IT_EMP::::::::: Now, only the data for the users defined in the netgroup IT_EMP is imported into war's password database and only these users are allowed to login. Unfortunately, this limitation also applies to the ~ function of the shell and all routines converting between user names and numerical user ids. In other words, cd ~user will not work, ls -l will show the numerical id instead of the username and find . -user joe -print will fail with No such user. To fix this, you will have to import all user entries without allowing them to login onto your servers. This can be achieved by adding another line to /etc/master.passwd. This line should contain +:::::::::/sbin/nologin, meaning Import all entries but replace the shell with /sbin/nologin in the imported entries. You can replace any field in the passwd entry by placing a default value in your /etc/master.passwd. Make sure that the line +:::::::::/sbin/nologin is placed after +@IT_EMP:::::::::. Otherwise, all user accounts imported from NIS will have /sbin/nologin as their login shell. After this change, you will only have to change one NIS map if a new employee joins the IT department. You could use a similar approach for the less important servers by replacing the old +::::::::: in their local version of /etc/master.passwd with something like this: +@IT_EMP::::::::: +@IT_APP::::::::: +:::::::::/sbin/nologin The corresponding lines for the normal workstations could be: +@IT_EMP::::::::: +@USERS::::::::: +:::::::::/sbin/nologin And everything would be fine until there is a policy change a few weeks later: The IT department starts hiring interns. The IT interns are allowed to use the normal workstations and the less important servers; and the IT apprentices are allowed to login onto the main servers. You add a new netgroup IT_INTERN, add the new IT interns to this netgroup and start to change the config on each and every machine... As the old saying goes: Errors in centralized planning lead to global mess. NIS' ability to create netgroups from other netgroups can be used to prevent situations like these. One possibility is the creation of role-based netgroups. For example, you could create a netgroup called BIGSRV to define the login restrictions for the important servers, another netgroup called SMALLSRV for the less important servers and a third netgroup called USERBOX for the normal workstations. Each of these netgroups contains the netgroups that are allowed to login onto these machines. The new entries for your NIS map netgroup should look like this: BIGSRV IT_EMP IT_APP SMALLSRV IT_EMP IT_APP ITINTERN USERBOX IT_EMP ITINTERN USERS This method of defining login restrictions works reasonably well if you can define groups of machines with identical restrictions. Unfortunately, this is the exception and not the rule. Most of the time, you will need the ability to define login restrictions on a per-machine basis. Machine-specific netgroup definitions are the other possibility to deal with the policy change outlined above. In this scenario, the /etc/master.passwd of each box contains two lines starting with ``+''. The first of them adds a netgroup with the accounts allowed to login onto this machine, the second one adds all other accounts with /sbin/nologin as shell. It is a good idea to use the ALL-CAPS version of the machine name as the name of the netgroup. In other words, the lines should look like this: +@BOXNAME::::::::: +:::::::::/sbin/nologin Once you have completed this task for all your machines, you will not have to modify the local versions of /etc/master.passwd ever again. All further changes can be handled by modifying the NIS map. Here is an example of a possible netgroup map for this scenario with some additional goodies. # Define groups of users first IT_EMP (,alpha,test-domain) (,beta,test-domain) IT_APP (,charlie,test-domain) (,delta,test-domain) DEPT1 (,echo,test-domain) (,foxtrott,test-domain) DEPT2 (,golf,test-domain) (,hotel,test-domain) DEPT3 (,india,test-domain) (,juliet,test-domain) ITINTERN (,kilo,test-domain) (,lima,test-domain) D_INTERNS (,able,test-domain) (,baker,test-domain) # # Now, define some groups based on roles USERS DEPT1 DEPT2 DEPT3 BIGSRV IT_EMP IT_APP SMALLSRV IT_EMP IT_APP ITINTERN USERBOX IT_EMP ITINTERN USERS # # And a groups for a special tasks # Allow echo and golf to access our anti-virus-machine SECURITY IT_EMP (,echo,test-domain) (,golf,test-domain) # # machine-based netgroups # Our main servers WAR BIGSRV FAMINE BIGSRV # User india needs access to this server POLLUTION BIGSRV (,india,test-domain) # # This one is really important and needs more access restrictions DEATH IT_EMP # # The anti-virus-machine mentioned above ONE SECURITY # # Restrict a machine to a single user TWO (,hotel,test-domain) # [...more groups to follow] If you are using some kind of database to manage your user accounts, you should be able to create the first part of the map with your database's report tools. This way, new users will automatically have access to the boxes. One last word of caution: It may not always be advisable to use machine-based netgroups. If you are deploying a couple dozen or even hundreds of identical machines for student labs, you should use role-based netgroups instead of machine-based netgroups to keep the size of the NIS map within reasonable limits. Important things to remember There are still a couple of things that you will need to do differently now that you are in an NIS environment. Every time you wish to add a user to the lab, you must add it to the master NIS server only, and you must remember to rebuild the NIS maps. If you forget to do this, the new user will not be able to login anywhere except on the NIS master. For example, if we needed to add a new user “jsmith” to the lab, we would: &prompt.root; pw useradd jsmith &prompt.root; cd /var/yp &prompt.root; make test-domain You could also run adduser jsmith instead of pw useradd jsmith. Keep the administration accounts out of the NIS maps. You don't want to be propagating administrative accounts and passwords to machines that will have users that shouldn't have access to those accounts. Keep the NIS master and slave secure, and minimize their downtime. If somebody either hacks or simply turns off these machines, they have effectively rendered many people without the ability to login to the lab. This is the chief weakness of any centralized administration system, and it is probably the most important weakness. If you do not protect your NIS servers, you will have a lot of angry users! NIS v1 compatibility FreeBSD's ypserv has some support for serving NIS v1 clients. FreeBSD's NIS implementation only uses the NIS v2 protocol, however other implementations include support for the v1 protocol for backwards compatibility with older systems. The ypbind daemons supplied with these systems will try to establish a binding to an NIS v1 server even though they may never actually need it (and they may persist in broadcasting in search of one even after they receive a response from a v2 server). Note that while support for normal client calls is provided, this version of ypserv does not handle v1 map transfer requests; consequently, it can not be used as a master or slave in conjunction with older NIS servers that only support the v1 protocol. Fortunately, there probably are not any such servers still in use today. NIS servers that are also NIS clients Care must be taken when running ypserv in a multi-server domain where the server machines are also NIS clients. It is generally a good idea to force the servers to bind to themselves rather than allowing them to broadcast bind requests and possibly become bound to each other. Strange failure modes can result if one server goes down and others are dependent upon on it. Eventually all the clients will time out and attempt to bind to other servers, but the delay involved can be considerable and the failure mode is still present since the servers might bind to each other all over again. You can force a host to bind to a particular server by running ypbind with the flag. libscrypt v.s. libdescrypt One of the most common issues that people run into when trying to implement NIS is crypt library compatibility. If your NIS server is using the DES crypt libraries, it will only support clients that are using DES as well. To check which one your server and clients are using look at the symlinks in /usr/lib. If the machine is configured to use the DES libraries, it will look something like this: &prompt.user; ls -l /usr/lib/*crypt* lrwxrwxrwx 1 root wheel 13 Jul 15 08:55 /usr/lib/libcrypt.a@ -> libdescrypt.a lrwxrwxrwx 1 root wheel 14 Jul 15 08:55 /usr/lib/libcrypt.so@ -> libdescrypt.so lrwxrwxrwx 1 root wheel 16 Jul 15 08:55 /usr/lib/libcrypt.so.2@ -> libdescrypt.so.2 lrwxrwxrwx 1 root wheel 15 Jul 15 08:55 /usr/lib/libcrypt_p.a@ -> libdescrypt_p.a -r--r--r-- 1 root wheel 13018 Nov 8 14:27 /usr/lib/libdescrypt.a lrwxr-xr-x 1 root wheel 16 Nov 8 14:27 /usr/lib/libdescrypt.so@ -> libdescrypt.so.2 -r--r--r-- 1 root wheel 12965 Nov 8 14:27 /usr/lib/libdescrypt.so.2 -r--r--r-- 1 root wheel 14750 Nov 8 14:27 /usr/lib/libdescrypt_p.a If the machine is configured to use the standard FreeBSD MD5 crypt libraries they will look something like this: &prompt.user; ls -l /usr/lib/*crypt* lrwxrwxrwx 1 root wheel 13 Jul 15 08:55 /usr/lib/libcrypt.a@ -> libscrypt.a lrwxrwxrwx 1 root wheel 14 Jul 15 08:55 /usr/lib/libcrypt.so@ -> libscrypt.so lrwxrwxrwx 1 root wheel 16 Jul 15 08:55 /usr/lib/libcrypt.so.2@ -> libscrypt.so.2 lrwxrwxrwx 1 root wheel 15 Jul 15 08:55 /usr/lib/libcrypt_p.a@ -> libscrypt_p.a -r--r--r-- 1 root wheel 6194 Nov 8 14:27 /usr/lib/libscrypt.a lrwxr-xr-x 1 root wheel 14 Nov 8 14:27 /usr/lib/libscrypt.so@ -> libscrypt.so.2 -r--r--r-- 1 root wheel 7579 Nov 8 14:27 /usr/lib/libscrypt.so.2 -r--r--r-- 1 root wheel 6684 Nov 8 14:27 /usr/lib/libscrypt_p.a If you have trouble authenticating on an NIS client, this is a pretty good place to start looking for possible problems. If you want to deploy an NIS server for a heterogenous network, you will probably have to use DES on all systems because it is the lowest common standard. DHCP Written by &a.gsutter;, March 2000. What is DHCP? DHCP, the Dynamic Host Configuration Protocol, describes the means by which a system can connect to a network and obtain the necessary information for communication upon that network. FreeBSD uses the ISC (Internet Software Consortium) DHCP implementation, so all implementation-specific information here is for use with the ISC distribution. What This Section Covers This handbook section attempts to describe only the parts of the DHCP system that are integrated with FreeBSD; consequently, the server portions are not described. The DHCP manual pages, in addition to the references below, are useful resources. How it Works When dhclient, the DHCP client, is executed on the client machine, it begins broadcasting requests for configuration information. By default, these requests are on UDP port 68. The server replies on UDP 67, giving the client an IP address and other relevant network information such as netmask, router, and DNS servers. All of this information comes in the form of a DHCP "lease" and is only valid for a certain time (configured by the DHCP server maintainer). In this manner, stale IP addresses for clients no longer connected to the network can be automatically reclaimed. DHCP clients can obtain a great deal of information from the server. An exhaustive list may be found in &man.dhcp-options.5;. FreeBSD Integration FreeBSD fully integrates the ISC DHCP client, dhclient. DHCP client support is provided within both the installer and the base system, obviating the need for detailed knowledge of network configurations on any network that runs a DHCP server. dhclient has been included in all FreeBSD distributions since 3.2. DHCP is supported by sysinstall. When configuring a network interface within sysinstall, the first question asked is, "Do you want to try dhcp configuration of this interface?" Answering affirmatively will execute dhclient, and if successful, will fill in the network configuration information automatically. There are two things you must do to have your system use DHCP upon startup: Make sure that the bpf device is compiled into your kernel. To do this, add pseudo-device bpf to your kernel configuration file, and rebuild the kernel. For more information about building kernels, see . The bpf device is already part of the GENERIC kernel that is supplied with FreeBSD, so if you don't have a custom kernel, you shouldn't need to create one in order to get DHCP working. For those who are particularly security conscious, you should be warned that bpf is also the device that allows packet sniffers to work correctly (although they still have to be run as root). bpf is required to use DHCP, but if you are very sensitive about security, you probably shouldn't add bpf to your kernel in the expectation that at some point in the future you will be using DHCP. Edit your /etc/rc.conf to include the following: ifconfig_fxp0="DHCP" Be sure to replace fxp0 with the designation for the interface that you wish to dynamically configure. If you are using a different location for dhclient, or if you wish to pass additional flags to dhclient, also include the following (editing as necessary): dhcp_program="/sbin/dhclient" dhcp_flags="" The DHCP server, dhcpd, is included as part of the isc-dhcp2 port in the ports collection. This port contains the full ISC DHCP distribution, consisting of client, server, relay agent and documentation. Files /etc/dhclient.conf dhclient requires a configuration file, /etc/dhclient.conf. Typically the file contains only comments, the defaults being reasonably sane. This configuration file is described by the &man.dhclient.conf.5; man page. /sbin/dhclient dhclient is statically linked and resides in /sbin. The &man.dhclient.8; manual page gives more information about dhclient. /sbin/dhclient-script dhclient-script is the FreeBSD-specific DHCP client configuration script. It is described in &man.dhclient-script.8;, but should not need any user modification to function properly. /var/db/dhclient.leases The DHCP client keeps a database of valid leases in this file, which is written as a log. &man.dhclient.leases.5; gives a slightly longer description. Further Reading The DHCP protocol is fully described in RFC 2131. An informational resource has also been set up at dhcp.org. + +DNS +Written by Chern Lee clee@serenivision.com, April 12, 2001. + + + + + Overview + FreeBSD utilizes, by default, a version of BIND (Berkeley Internet Name + Domain), which is the most common implementation of the DNS protocol. DNS + is the protocol through which names are mapped to ips, and vice + versa. For example, a query for www.freebsd.org will send back a reply + for the IP address of The FreeBSD Project's webpage, whereas, a query for + ftp.freebsd.org will return the IP of the corresponding ftp + machine. Likewise, the opposite can happen. A query for an ip address + can resolve its hostname. + + + DNS is coordinated across the Internet through a somewhat complex system + of authoritative root name servers, and other smaller-scale nameservers + who host and relay individual domain information. + + + + This document refers to BIND 8.x, as it is the most current, stable + version used in FreeBSD. + + + + RFC1034 and RFC1035 dictates the DNS protocol. + + + + Currently, BIND is maintained by the + Internet Software Consortium (www.isc.org) + + + + + Terminology Used + + zone - Each individual domain, subdomain, + or 'area' dictated by DNS is considered a zone. + + + Examples of zones: + + + + . is the root zone + + + org. is a zone under the root zone + + + foobardomain.org is a zone under the org. zone + + + foo.foobardomain.org. is a subdomain, a zone under the + foobardomain.org. zone + + + + + 1.2.3.in-addr.arpa is a zone referencing all ips which fall under + the 3.2.1.* ip space. + + + + + named, bind, name server - these are all common + names for the BIND name server package within FreeBSD. + + + resolver - a network process by which a system + queries a nameserver for answers + + + root zone - literally, a '.', refers to the root, + or beginning zone. All zones fall under this, as do all files in fall + under the root directory. It is the beginning of the Internet zone + hierarchy + + + origin - refers to the point of start for the + particular zone + + + forward dns - mapping of hostnames to ip addresses + + + reverse dns - the opposite, mapping of ip + addresses to hostnames + + + + + Reasons to run a name server + + + + You need your machine to host DNS information to the world + + + + An authoritative nameserver replies exclusively + to requests. + + + + For example, you register foobardomain.org and wish to assign + hostnames to its proper ip addresses. + + + + A slave nameserver, which replies to queries for a + domain when the primary is down or inaccessible. + + + + The above two can also be done with in-addr.arpa, ip to + hostname entries + + + + + + + You wish your machine to act as a local relay of DNS + information + + + + DNS traffic has been measured to be about 5% or more of + the total Internet traffic. + + + + A local DNS server may have some added benefit by + providing a local cache of DNS information. + + + + + For example, when one queries for www.freebsd.org, their + resolver goes out to (usually) your ISP's name server, and + retreives the query. + + + + + With a local, caching DNS server, the query only has to be + made once to the outside world. Every additional query will + not have to go outside of the local network, since the + information is cached. + + + + + + + + +How it works + + A DNS server in FreeBSD relies on the BIND daemon. This daemon is + called 'named' for obvious reasons. + + + named - the bind daemon + ndc - name daemon control program + + + /etc/namedb - directory where all the bind information + resides + + + /etc/namedb/named.conf - daemon configuration file + + + + zone files are usually contained within the /etc/namedb + directory, and contain the information (query answers from your site) + served by your name server. + + + + + Starting BIND + + Since bind is installed by default, configuring it all is relatively + simple. + + + To ensure the named daemon is started at boot, put the following + modifications in your /etc/rc.conf + + named_enable="YES" + To start the daemon manually (after configuring it) + &prompt.root; ndc start + + + + Configuration files + + make-localhost + Be sure to + + + &prompt.root; cd /etc/namedb + &prompt.root; sh make-localhost + + to properly create your local reverse dns zone file in + /etc/namedb/localhost.rev. + + + + + <filename>/etc/namedb/named.conf</filename> + + +// $FreeBSD: src/etc/namedb/named.conf,v 1.6.2.1 2000/07/15 07:49:29 kris Exp $ +// +// Refer to the named(8) man page for details. If you are ever going +// to setup a primary server, make sure you've understood the hairy +// details of how DNS is working. Even with simple mistakes, you can +// break connectivity for affected parties, or cause huge amount of +// useless Internet traffic. + +options { + directory "/etc/namedb"; + +// In addition to the "forwarders" clause, you can force your name +// server to never initiate queries of its own, but always ask its +// forwarders only, by enabling the following line: +// +// forward only; + +// If you've got a DNS server around at your upstream provider, enter +// its IP address here, and enable the line below. This will make you +// benefit from its cache, thus reduce overall DNS traffic in the +Internet. +/* + forwarders { + 127.0.0.1; + }; +*/ + + + + Just as the comment says, if you want to benefit from your uplink's + cache, you can enable this section of the config file. + + Normally, your nameserver will recursively query different nameservers + until it finds the answer it is looking for. Having this enabled will + have it automatically see if your uplink's (or whatever provided) ns + has the requested query. + + If your uplink has a heavily trafficked, fast nameserver, enabling + this properly could work to your advantage. + + 127.0.0.1 will *NOT* work here; change this to the ip of a nameserver + at your uplink. + + + + /* + * If there is a firewall between you and nameservers you want + * to talk to, you might need to uncomment the query-source + * directive below. Previous versions of BIND always asked + * questions using port 53, but BIND 8.1 uses an unprivileged + * port by default. + */ + // query-source address * port 53; + + /* + * If running in a sandbox, you may have to specify a different + * location for the dumpfile. + */ + // dump-file "s/named_dump.db"; +}; + +// Note: the following will be supported in a future release. +/* +host { any; } { + topology { + 127.0.0.0/8; + }; +}; +*/ + +// Setting up secondaries is way easier and the rough picture for this +// is explained below. +// +// If you enable a local name server, don't forget to enter 127.0.0.1 +// into your /etc/resolv.conf so this server will be queried first. +// Also, make sure to enable it in /etc/rc.conf. + +zone "." { + type hint; + file "named.root"; +}; + +zone "0.0.127.IN-ADDR.ARPA" { + type master; + file "localhost.rev"; +}; + +zone +"0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.INT" { + type master; + file "localhost.rev"; +}; + +// NB: Do not use the IP addresses below, they are faked, and only +// serve demonstration/documentation purposes! +// +// Example secondary config entries. It can be convenient to become +// a secondary at least for the zone where your own domain is in. Ask +// your network administrator for the IP address of the responsible +// primary. +// +// Never forget to include the reverse lookup (IN-ADDR.ARPA) zone! +// (This is the first bytes of the respective IP address, in reverse +// order, with ".IN-ADDR.ARPA" appended.) +// +// Before starting to setup a primary zone, better make sure you fully +// understand how DNS and BIND works, however. There are sometimes +// unobvious pitfalls. Setting up a secondary is comparably simpler. +// +// NB: Don't blindly enable the examples below. :-) Use actual names +// and addresses instead. +// +// NOTE!!! FreeBSD runs bind in a sandbox (see named_flags in rc.conf). +// The directory containing the secondary zones must be write accessible +// to bind. The following sequence is suggested: +// +// mkdir /etc/namedb/s +// chown bind.bind /etc/namedb/s +// chmod 750 /etc/namedb/s + +/* +zone "domain.com" { + type slave; + file "s/domain.com.bak"; + masters { + 192.168.1.1; + }; +}; + +zone "0.168.192.in-addr.arpa" { + type slave; + file "s/0.168.192.in-addr.arpa.bak"; + masters { + 192.168.1.1; + }; +}; +*/ + + + These are example slave entries, read below to see more. + + + For each new domain added to your nameserver, you must add one of + these entries to your named.conf + + + The simplest zone entry, can look like + + +zone "foobardomain.org" { + type master; + file "foorbardomain.org"; +}; + + + For a master entry with the zone information within + foobardomain.org, or + + + +zone "foobardomain.org" { + type slave; + file "foobardomain.org"; +}; + + + + for a slave. Note that slave zones automatically query the listed + master (authoritative) name servers for the zone file. + + + + + Zone files + + An example master 'foobardomain.org' (existing within + /etc/namedb/foobardomain.org) is as follows: + + + +$TTL 3600 + +foobardomain.org. IN SOA ns1.foobardomain.org. admin.foobardomain.org. ( + 5 ; Serial + 10800 ; Refresh + 3600 ; Retry + 604800 ; Expire + 86400 ) ; Minimum TTL + +; DNS Servers +@ IN NS ns1.foobardomain.org. +@ IN NS ns2.foobardomain.org. + +; Machine Names +localhost IN A 127.0.0.1 +ns1 IN A 3.2.1.2 +ns2 IN A 3.2.1.3 +mail IN A 3.2.1.10 +@ IN A 3.2.1.30 + +; Aliases +www IN CNAME @ + +; MX Record +@ IN MX 10 mail.foobardomain.org. + + + + Note that every hostname ending in a '.' is an exact hostname, whereas + everything without a trailing '.' is referenced to the origin. For + example, www is transalated into www + origin. In our ficitious zone + file, our origin is foobardomain.org, so www would be + www.foobardomain.org. + + + + The format of this file follows: + + recordname IN recordtype value + + + The most commonly used DNS records: + + SOA - start of zone authority + NS - an authoritative nameserver + A - A host address + CNAME - the canonical name for an alias + MX - mail exchange + PTR - a domain name pointer (used in reverse + dns) + +foobardomain.org. IN SOA ns1.foobardomain.org. admin.foobardomain.org. ( + 5 ; Serial + 10800 ; Refresh after 3 hours + 3600 ; Retry after 1 hour + 604800 ; Expire after 1 week + 86400 ) ; Minimum TTL of 1 day + + + foobardomain.org. - the domain name, also the + origin for this zone file. + + ns1.foobardomain.org. - the + primary/authoritative nameserver for this zone + + admin.foobardomain.org. - the responsible + person for this zone, e-mail address with @ replaced. + (admin@foobardomain.org becomes admin.foobardomain.org) + + + 5 - the serial number of the file. this must be + incremented each time the zone file is modified. Nowadays, many + admins prefer a yyyymmddrr format for the serial number. 2001041002 + would mean last modified 04/10/2001, the latter 02 being the second + time the zone file has been modified this day. The serial number is + important as it alerts slave nameservers for a zone when it is updated. + + + +@ IN NS ns1.foobardomain.org. + + + This is an NS entry. Every nameserver that is going to reply + authoritatively for the zone must have one of these entries. The @ + is seen here could have been 'foobardomain.org.' The @ transalates to + the origin. + + + +localhost IN A 127.0.0.1 +ns1 IN A 3.2.1.2 +ns2 IN A 3.2.1.3 +mail IN A 3.2.1.10 +@ IN A 3.2.1.30 + + + The A record indicates machine names. As seen above, + ns1.foobardomain.org would resolve to 3.2.1.2. Again, the origin + symbol, @, is used here, thus meaning foobardomain.org would resolve + to 3.2.1.30. + + + +www IN CNAME @ + + + The canonical name record is usually used for giving aliases to a + machine. In the example, www is aliased to the machine addressed to + the origin, or foobardomain.org (3.2.1.30). CNAMEs can be used to + provide alias hostnames, or round robin one hostname among multiple + machines. + + + +@ IN MX 10 mail.foobardomain.org. + + + + The MX record indictes which mail servers are responsible for handling + incoming mail for the zone. mail.foobardomain.org is the hostname of + the mail server, and 10 being the priority of that mailserver. + + + + One can have several mailservers, with priorities of 3, 2, 1. A mail + server attempting to deliver to foobardomain.org would first try the + highest priority MX, then the second highest, etc, until the mail can + be properly delivered. + + + + For in-addr.arpa zone files (reverse dns), the same format is used, + except with PTR entries instead of A or CNAME. + + + +$TTL 3600 + +1.2.3.in-addr.arpa. IN SOA ns1.foobardomain.org. admin.foobardomain.org. ( + 5 ; Serial + 10800 ; Refresh + 3600 ; Retry + 604800 ; Expire + 3600 ) ; Minimum + +@ IN NS ns1.foobardomain.org. +@ IN NS ns2.foobardomain.org. + +2 IN PTR ns1.foobardomain.org. +3 IN PTR ns2.foobardomain.org. +10 IN PTR mail.foobardomain.org. +30 IN PTR foobardomain.org. + + + This file gives the proper ip to hostname mappings of our above + ficticious domain. + + + + + + Caching Name Server + + A caching nameserver is simply a nameserver that is not authoritative for + any zones. It simply asks queries of its own, and remembers them for + later use. To set one up, just configure the name server as usual, omitting any inclusions of zones. + + + + + How to use the nameserver + + If setup properly, the nameserver should be accessible through the + network and locally. /etc/resolv.conf must contain + a nameserver entry with the local ip so it will query the local name + server first. + + + + To access it over the network, the machine must have the nameserver's ip + set properly in its own nameserver configuration options. + + + + + Security + + Although BIND is the most common implementation of DNS, there is + always the issue of security. Possible and exploitable security holes + are sometimes found. + + + + It is a good idea to subscribe to CERT + and + freebsd-announce + to stay up to date with the current Internet and FreeBSD security issues. + + + + If a problem arises, keeping your sources up to date and having a fresh + build of named can't hurt. + + + + + Further Reading + + &man.ndc.8; &man.named.8; &man.named.conf.5; + + + + Official ISC BIND Page + http://www.isc.org/products/BIND/ + + + + BIND FAQ + + http://www.nominum.com/resources/faqs/bind-faqs.html + + + + O'Reilly DNS and BIND 4th Edition + + + + RFC1034 - Domain Names - + Concepts and Facilities + + + + RFC1035 - Domain Names - + Implementation and Specification + + + + + - diff --git a/en_US.ISO_8859-1/books/handbook/advanced-networking/chapter.sgml b/en_US.ISO_8859-1/books/handbook/advanced-networking/chapter.sgml index 6cde4ef3a6..cd443d65b5 100644 --- a/en_US.ISO_8859-1/books/handbook/advanced-networking/chapter.sgml +++ b/en_US.ISO_8859-1/books/handbook/advanced-networking/chapter.sgml @@ -1,2717 +1,3357 @@ Advanced Networking Synopsis The following chapter will cover some of the more frequently used network services on UNIX systems. This, of course, will pertain to configuring said services on your FreeBSD system. Gateways and Routes Contributed by &a.gryphon;. 6 October 1995. For one machine to be able to find another, there must be a mechanism in place to describe how to get from one to the other. This is called Routing. A route is a defined pair of addresses: a destination and a gateway. The pair indicates that if you are trying to get to this destination, send along through this gateway. There are three types of destinations: individual hosts, subnets, and default. The default route is used if none of the other routes apply. We will talk a little bit more about default routes later on. There are also three types of gateways: individual hosts, interfaces (also called links), and ethernet hardware addresses. An example To illustrate different aspects of routing, we will use the following example which is the output of the command netstat -r: Destination Gateway Flags Refs Use Netif Expire default outside-gw UGSc 37 418 ppp0 localhost localhost UH 0 181 lo0 test0 0:e0:b5:36:cf:4f UHLW 5 63288 ed0 77 10.20.30.255 link#1 UHLW 1 2421 foobar.com link#1 UC 0 0 host1 0:e0:a8:37:8:1e UHLW 3 4601 lo0 host2 0:e0:a8:37:8:1e UHLW 0 5 lo0 => host2.foobar.com link#1 UC 0 0 224 link#1 UC 0 0 The first two lines specify the default route (which we will cover in the next section) and the localhost route. The interface (Netif column) that it specifies to use for localhost is lo0, also known as the loopback device. This says to keep all traffic for this destination internal, rather than sending it out over the LAN, since it will only end up back where it started anyway. The next thing that stands out are the 0:e0:... addresses. These are ethernet hardware addresses. FreeBSD will automatically identify any hosts (test0 in the example) on the local ethernet and add a route for that host, directly to it over the ethernet interface, ed0. There is also a timeout (Expire column) associated with this type of route, which is used if we fail to hear from the host in a specific amount of time. In this case the route will be automatically deleted. These hosts are identified using a mechanism known as RIP (Routing Information Protocol), which figures out routes to local hosts based upon a shortest path determination. FreeBSD will also add subnet routes for the local subnet (10.20.30.255 is the broadcast address for the subnet 10.20.30, and foobar.com is the domain name associated with that subnet). The designation link#1 refers to the first ethernet card in the machine. You will notice no additional interface is specified for those. Both of these groups (local network hosts and local subnets) have their routes automatically configured by a daemon called routed. If this is not run, then only routes which are statically defined (ie. entered explicitly) will exist. The host1 line refers to our host, which it knows by ethernet address. Since we are the sending host, FreeBSD knows to use the loopback interface (lo0) rather than sending it out over the ethernet interface. The two host2 lines are an example of what happens when we use an ifconfig alias (see the section of ethernet for reasons why we would do this). The => symbol after the lo0 interface says that not only are we using the loopback (since this is address also refers to the local host), but specifically it is an alias. Such routes only show up on the host that supports the alias; all other hosts on the local network will simply have a link#1 line for such. The final line (destination subnet 224) deals with MultiCasting, which will be covered in a another section. The other column that we should talk about are the Flags. Each route has different attributes that are described in the column. Below is a short table of some of these flags and their meanings: U Up: The route is active. H Host: The route destination is a single host. G Gateway: Send anything for this destination on to this remote system, which will figure out from there where to send it. S Static: This route was configured manually, not automatically generated by the system. C Clone: Generates a new route based upon this route for machines we connect to. This type of route is normally used for local networks. W WasCloned: Indicated a route that was auto-configured based upon a local area network (Clone) route. L Link: Route involves references to ethernet hardware. Default routes When the local system needs to make a connection to remote host, it checks the routing table to determine if a known path exists. If the remote host falls into a subnet that we know how to reach (Cloned routes), then the system checks to see if it can connect along that interface. If all known paths fail, the system has one last option: the default route. This route is a special type of gateway route (usually the only one present in the system), and is always marked with a c in the flags field. For hosts on a local area network, this gateway is set to whatever machine has a direct connection to the outside world (whether via PPP link, or your hardware device attached to a dedicated data line). If you are configuring the default route for a machine which itself is functioning as the gateway to the outside world, then the default route will be the gateway machine at your Internet Service Provider's (ISP) site. Let us look at an example of default routes. This is a common configuration: [Local2] <--ether--> [Local1] <--PPP--> [ISP-Serv] <--ether--> [T1-GW] The hosts Local1 and Local2 are at your site, with the formed being your PPP connection to your ISP's Terminal Server. Your ISP has a local network at their site, which has, among other things, the server where you connect and a hardware device (T1-GW) attached to the ISP's Internet feed. The default routes for each of your machines will be: host default gateway interface Local2 Local1 ethernet Local1 T1-GW PPP A common question is Why (or how) would we set the T1-GW to be the default gateway for Local1, rather than the ISP server it is connected to?. Remember, since the PPP interface is using an address on the ISP's local network for your side of the connection, routes for any other machines on the ISP's local network will be automatically generated. Hence, you will already know how to reach the T1-GW machine, so there is no need for the intermediate step of sending traffic to the ISP server. As a final note, it is common to use the address ...1 as the gateway address for your local network. So (using the same example), if your local class-C address space was 10.20.30 and your ISP was using 10.9.9 then the default routes would be: Local2 (10.20.30.2) --> Local1 (10.20.30.1) Local1 (10.20.30.1, 10.9.9.30) --> T1-GW (10.9.9.1) Dual homed hosts There is one other type of configuration that we should cover, and that is a host that sits on two different networks. Technically, any machine functioning as a gateway (in the example above, using a PPP connection) counts as a dual-homed host. But the term is really only used to refer to a machine that sits on two local-area networks. In one case, the machine as two ethernet cards, each having an address on the separate subnets. Alternately, the machine may only have one ethernet card, and be using ifconfig aliasing. The former is used if two physically separate ethernet networks are in use, the latter if there is one physical network segment, but two logically separate subnets. Either way, routing tables are set up so that each subnet knows that this machine is the defined gateway (inbound route) to the other subnet. This configuration, with the machine acting as a Bridge between the two subnets, is often used when we need to implement packet filtering or firewall security in either or both directions. Routing propagation We have already talked about how we define our routes to the outside world, but not about how the outside world finds us. We already know that routing tables can be set up so that all traffic for a particular address space (in our examples, a class-C subnet) can be sent to a particular host on that network, which will forward the packets inbound. When you get an address space assigned to your site, your service provider will set up their routing tables so that all traffic for your subnet will be sent down your PPP link to your site. But how do sites across the country know to send to your ISP? There is a system (much like the distributed DNS information) that keeps track of all assigned address-spaces, and defines their point of connection to the Internet Backbone. The Backbone are the main trunk lines that carry Internet traffic across the country, and around the world. Each backbone machine has a copy of a master set of tables, which direct traffic for a particular network to a specific backbone carrier, and from there down the chain of service providers until it reaches your network. It is the task of your service provider to advertise to the backbone sites that they are the point of connection (and thus the path inward) for your site. This is known as route propagation. Troubleshooting Sometimes, there is a problem with routing propagation, and some sites are unable to connect to you. Perhaps the most useful command for trying to figure out where a routing is breaking down is the &man.traceroute.8; command. It is equally useful if you cannot seem to make a connection to a remote machine (i.e. &man.ping.8; fails). The &man.traceroute.8; command is run with the name of the remote host you are trying to connect to. It will show the gateway hosts along the path of the attempt, eventually either reaching the target host, or terminating because of a lack of connection. For more information, see the manual page for &man.traceroute.8;. Bridging Written by Steve Peterson steve@zpfe.com. Introduction It is sometimes useful to divide one physical network (i.e., an Ethernet segment) into two separate network segments, without having to create IP subnets and use a router to connect the segments together. A device that connects two networks together in this fashion is called a bridge. and a FreeBSD system with two network interface cards can act as a bridge. The bridge works by learning the MAC layer addresses (i.e., Ethernet addresses) of the devices on each of its network interfaces. It forwards traffic between two networks only when its source and destination are on different networks. In many respects, a bridge is like an Ethernet switch with very few ports. Situations where bridging is appropriate There are two common situations in which a bridge is used today. High traffic on a segment Situation one is where your physical network segment is overloaded with traffic, but you don't want for whatever reason to subnet the network and interconnect the subnets with a router. Let's consider an example of a newspaper where the Editorial and Production departments are on the same subnetwork. The Editorial users all use server A for file service, and the Production users are on server B. An Ethernet is used to connect all users together, and high loads on the network are slowing things down. If the Editorial users could be segregated on one network segment and the Production users on another, the two network segments could be connected with a bridge. Only the network traffic destined for interfaces on the "other" side of the bridge would be sent to the other network, reducing congestion on each network segment. Filtering/traffic shaping firewall The second common situation is where firewall functionality is needed without IP Masquerading (NAT). An example is a small company that is connected via DSL or ISDN to their ISP. They have a 13 address global IP allocation for their ISP and have 10 PCs on their network. In this situation, using a router-based firewall is difficult because of subnetting issues. A bridge-based firewall can be configured and dropped into the path just downstream of their DSL/ISDN router without any IP numbering issues. Configuring a bridge Network interface card selection A bridge requires at least two network cards to function. Unfortunately, not all network interface cards as of FreeBSD 4.0 support bridging. Read &man.bridge.4; for details on the cards that are supported. Install and test the two network cards before continuing. Kernel configuration changes To enable kernel support for bridging, add the options BRIDGE statement to your kernel configuration file, and rebuild your kernel. Firewall support If you are planning to use the bridge as a firewall, you will need to add the IPFIREWALL option as well. Read for general information on configuring the bridge as a firewall. If you need to allow non-IP packets (such as ARP) to flow through the bridge, there is an undocumented firewall option that must be set. This option is IPFIREWALL_DEFAULT_TO_ACCEPT. Note that this changes the default rule for the firewall to accept any packet. Make sure you know how this changes the meaning of your ruleset before you set it. Traffic shaping support If you want to use the bridge as a traffic shaper, you will need to add the DUMMYNET option to your kernel configuration. Read &man.dummynet.4; for further information. Enabling the bridge Add the line net.link.ether.bridge=1 to /etc/sysctl.conf to enable the bridge at runtime. If you want the bridged packets to be filtered by ipfw, you should also add net.link.ether.bridge_ipfw=1 as well. Performance My bridge/firewall is a Pentium 90 with one 3Com 3C900B and one 3C905B. The protected side of the network runs at 10mbps half duplex and the connection between the bridge and my router (a Cisco 675) runs at 100mbps full duplex. With no filtering enabled, I've found that the bridge adds about 0.4 milliseconds of latency to pings from the protected 10mbps network to the Cisco 675. Other information If you want to be able to telnet into the bridge from the network, it is OK to assign one of the network cards an IP address. The consensus is that assigning both cards an address is a bad idea. If you have multiple bridges on your network, there cannot be more than one path between any two workstations. Technically, this means that there is no support for spanning tree link management. NFS Written by &a.unfurl;, 4 March 2000. Among the many different file systems that FreeBSD supports is a very unique type, the Network File System or NFS. NFS allows you to share directories and files on one machine with one or more other machines via the network they are attached to. Using NFS, users and programs can access files on remote systems as if they were local files. NFS has several benefits: Local workstations dont need as much disk space because commonly used data can be stored on a single machine and still remain accessible to everyone on the network. There is no need for users to have unique home directories on every machine on your network. Once they have an established directory that is available via NFS it can be accessed from anywhere. Storage devices such as floppies and CD-ROM drives can be used by other machines on the network eliminating the need for extra hardware. How It Works NFS is composed of two sides – a client side and a server side. Think of it as a want/have relationship. The client wants the data that the server side has. The server shares its data with the client. In order for this system to function properly a few processes have to be configured and running properly. The server has to be running the following daemons: nfsd - The NFS Daemon which services requests from NFS clients. mountd - The NFS Mount Daemon which actually carries out requests that nfsd passes on to it. portmap - The portmapper daemon which allows NFS clients to find out which port the NFS server is using. The client side only needs to run a single daemon: nfsiod - The NFS async I/O Daemon which services requests from its NFS server. Configuring NFS Luckily for us, on a FreeBSD system this setup is a snap. The processes that need to be running can all be run at boot time with a few modifications to your /etc/rc.conf file. On the NFS server make sure you have: portmap_enable="YES" nfs_server_enable="YES" nfs_server_flags="-u -t -n 4" mountd_flags="-r" mountd is automatically run whenever the NFS server is enabled. The and flags to nfsd tell it to serve UDP and TCP clients. The flag tells nfsd to start 4 copies of itself. On the client, make sure you have: nfs_client_enable="YES" nfs_client_flags="-n 4" Like nfsd, the tells nfsiod to start 4 copies of itself. The last configuration step requires that you create a file called /etc/exports. The exports file specifies which file systems on your server will be shared (a.k.a., exported) and with what clients they will be shared. Each line in the file specifies a file system to be shared. There are a handful of options that can be used in this file but I will only touch on a few of them. You can find out about the rest in the &man.exports.5; man page. Here are a few example /etc/exports entries: The following line exports /cdrom to three silly machines that have the same domain name as the server (hence the lack of a domain name for each) or have entries in your /etc/hosts file. The flag makes the shared file system read-only. With this flag, the remote system will not be able to make any changes to the the shared file system. /cdrom -ro moe larry curly The following line exports /home to three hosts by IP address. This is a useful setup if you have a private network but do not have DNS running. The flag allows all the directories below the specified file system to be exported as well. /home -alldirs 10.0.0.2 10.0.0.3 10.0.0.4 The following line exports /a to two machines that have different domain names than the server. The flag allows the root user on the remote system to write to the shared file system as root. Without the -maproot=0 flag even if someone has root access on the remote system they won't be able to modify files on the shared file system. /a -maproot=0 host.domain.com box.example.com In order for a client to share an exported file system it must have permission to do so. Make sure your client is listed in your /etc/exports file. Now that you have made all these changes you can just reboot and let FreeBSD start everything for you at boot time or you can run the following commands as root: On the NFS server: &prompt.root; portmap &prompt.root; nfsd -u -t -n 4 &prompt.root; mountd -r On the NFS client: &prompt.root; nfsiod -n 4 Now you should be ready to actually mount a remote file system. This can be done one of two ways. In these examples the server's name will be server and the client's name will be client. If you just want to temporarily mount a remote file system or just want to test out your config you can run a command like this as root on the client: &prompt.root; mount server:/home /mnt This will mount /home on the server on /mnt on the client. If everything is setup correctly you should be able to go into /mnt on the client and see all the files that are on the server. If you want to permanently (each time you reboot) mount a remote file system you need to add it to your /etc/fstab file. Here is an example line: server:/home /mnt nfs rw 0 0 Read the &man.fstab.5; man page for more options. Practical Uses There are many very cool uses for NFS. I use it quite a bit on the LAN I admin. Here are a few ways I have found it to be useful. I have several machines on my network but only one of them has a CD-ROM drive. Why? Because I have that one CD-ROM drive shared with all the others via NFS. The same can be done with floppy drives. With so many machines on the network it gets old having your personal files strewn all over the place. I have a central NFS server that houses all user home directories and shares them with the rest of the machines on the LAN, so no matter where I login I have the same home directory. When you get to reinstalling FreeBSD on one of your machines, NFS is the way to go. Just pop your distribution CD into your file server and away you go. I have a common /usr/ports/distfiles directory that all my machines share. That way when I go to install a port that I already installed on a different machine I do not have to download the source all over again. Problems integrating with other systems Contributed by &a.jlind;. Certain Ethernet adapters for ISA PC systems have limitations which can lead to serious network problems, particularly with NFS. This difficulty is not specific to FreeBSD, but FreeBSD systems are affected by it. The problem nearly always occurs when (FreeBSD) PC systems are networked with high-performance workstations, such as those made by Silicon Graphics, Inc., and Sun Microsystems, Inc. The NFS mount will work fine, and some operations may succeed, but suddenly the server will seem to become unresponsive to the client, even though requests to and from other systems continue to be processed. This happens to the client system, whether the client is the FreeBSD system or the workstation. On many systems, there is no way to shut down the client gracefully once this problem has manifested itself. The only solution is often to reset the client, because the NFS situation cannot be resolved. Though the correct solution is to get a higher performance and capacity Ethernet adapter for the FreeBSD system, there is a simple workaround that will allow satisfactory operation. If the FreeBSD system is the server, include the option on the mount from the client. If the FreeBSD system is the client, then mount the NFS file system with the option . These options may be specified using the fourth field of the fstab entry on the client for automatic mounts, or by using the parameter of the mount command for manual mounts. It should be noted that there is a different problem, sometimes mistaken for this one, when the NFS servers and clients are on different networks. If that is the case, make certain that your routers are routing the necessary UDP information, or you will not get anywhere, no matter what else you are doing. In the following examples, fastws is the host (interface) name of a high-performance workstation, and freebox is the host (interface) name of a FreeBSD system with a lower-performance Ethernet adapter. Also, /sharedfs will be the exported NFS filesystem (see man exports), and /project will be the mount point on the client for the exported file system. In all cases, note that additional options, such as or and may be desirable in your application. Examples for the FreeBSD system (freebox) as the client: in /etc/fstab on freebox: fastws:/sharedfs /project nfs rw,-r=1024 0 0 As a manual mount command on freebox: &prompt.root; mount -t nfs -o -r=1024 fastws:/sharedfs /project Examples for the FreeBSD system as the server: in /etc/fstab on fastws: freebox:/sharedfs /project nfs rw,-w=1024 0 0 As a manual mount command on fastws: &prompt.root; mount -t nfs -o -w=1024 freebox:/sharedfs /project Nearly any 16-bit Ethernet adapter will allow operation without the above restrictions on the read or write size. For anyone who cares, here is what happens when the failure occurs, which also explains why it is unrecoverable. NFS typically works with a block size of 8k (though it may do fragments of smaller sizes). Since the maximum Ethernet packet is around 1500 bytes, the NFS block gets split into multiple Ethernet packets, even though it is still a single unit to the upper-level code, and must be received, assembled, and acknowledged as a unit. The high-performance workstations can pump out the packets which comprise the NFS unit one right after the other, just as close together as the standard allows. On the smaller, lower capacity cards, the later packets overrun the earlier packets of the same unit before they can be transferred to the host and the unit as a whole cannot be reconstructed or acknowledged. As a result, the workstation will time out and try again, but it will try again with the entire 8K unit, and the process will be repeated, ad infinitum. By keeping the unit size below the Ethernet packet size limitation, we ensure that any complete Ethernet packet received can be acknowledged individually, avoiding the deadlock situation. Overruns may still occur when a high-performance workstations is slamming data out to a PC system, but with the better cards, such overruns are not guaranteed on NFS units. When an overrun occurs, the units affected will be retransmitted, and there will be a fair chance that they will be received, assembled, and acknowledged. Diskless Operation Contributed by &a.martin;. netboot.com/netboot.rom allow you to boot your FreeBSD machine over the network and run FreeBSD without having a disk on your client. Under 2.0 it is now possible to have local swap. Swapping over NFS is also still supported. Supported Ethernet cards include: Western Digital/SMC 8003, 8013, 8216 and compatibles; NE1000/NE2000 and compatibles (requires recompile) Setup Instructions Find a machine that will be your server. This machine will require enough disk space to hold the FreeBSD 2.0 binaries and have bootp, tftp and NFS services available. Tested machines: HP9000/8xx running HP-UX 9.04 or later (pre 9.04 doesn't work) Sun/Solaris 2.3. (you may need to get bootp) Set up a bootp server to provide the client with IP, gateway, netmask. diskless:\ :ht=ether:\ :ha=0000c01f848a:\ :sm=255.255.255.0:\ :hn:\ :ds=192.1.2.3:\ :ip=192.1.2.4:\ :gw=192.1.2.5:\ :vm=rfc1048: Set up a TFTP server (on same machine as bootp server) to provide booting information to client. The name of this file is cfg.X.X.X.X (or /tftpboot/cfg.X.X.X.X, it will try both) where X.X.X.X is the IP address of the client. The contents of this file can be any valid netboot commands. Under 2.0, netboot has the following commands: help print help list ip print/set client's IP address server print/set bootp/tftp server address netmask print/set netmask hostname name print/set hostname kernel print/set kernel name rootfs print/set root filesystem swapfs print/set swap filesystem swapsize set diskless swapsize in KBytes diskboot boot from disk autoboot continue boot process trans | turn transceiver on|off flags set boot flags A typical completely diskless cfg file might contain: rootfs 192.1.2.3:/rootfs/myclient swapfs 192.1.2.3:/swapfs swapsize 20000 hostname myclient.mydomain A cfg file for a machine with local swap might contain: rootfs 192.1.2.3:/rootfs/myclient hostname myclient.mydomain Ensure that your NFS server has exported the root (and swap if applicable) filesystems to your client, and that the client has root access to these filesystems A typical /etc/exports file on FreeBSD might look like: /rootfs/myclient -maproot=0:0 myclient.mydomain /swapfs -maproot=0:0 myclient.mydomain And on HP-UX: /rootfs/myclient -root=myclient.mydomain /swapfs -root=myclient.mydomain If you are swapping over NFS (completely diskless configuration) create a swap file for your client using dd. If your swapfs command has the arguments /swapfs and the size 20000 as in the example above, the swapfile for myclient will be called /swapfs/swap.X.X.X.X where X.X.X.X is the client's IP addr, e.g.: &prompt.root; dd if=/dev/zero of=/swapfs/swap.192.1.2.4 bs=1k count=20000 Also, the client's swap space might contain sensitive information once swapping starts, so make sure to restrict read and write access to this file to prevent unauthorized access: &prompt.root; chmod 0600 /swapfs/swap.192.1.2.4 Unpack the root filesystem in the directory the client will use for its root filesystem (/rootfs/myclient in the example above). On HP-UX systems: The server should be running HP-UX 9.04 or later for HP9000/800 series machines. Prior versions do not allow the creation of device files over NFS. When extracting /dev in /rootfs/myclient, beware that some systems (HPUX) will not create device files that FreeBSD is happy with. You may have to go to single user mode on the first bootup (press control-c during the bootup phase), cd /dev and do a sh ./MAKEDEV all from the client to fix this. Run netboot.com on the client or make an EPROM from the netboot.rom file Using Shared <filename>/</filename> and <filename>/usr</filename> filesystems At present there isn't an officially sanctioned way of doing this, although I have been using a shared /usr filesystem and individual / filesystems for each client. If anyone has any suggestions on how to do this cleanly, please let me and/or the &a.core; know. Compiling netboot for specific setups Netboot can be compiled to support NE1000/2000 cards by changing the configuration in /sys/i386/boot/netboot/Makefile. See the comments at the top of this file. ISDN Last modified by &a.wlloyd;. A good resource for information on ISDN technology and hardware is Dan Kegel's ISDN Page. A quick simple road map to ISDN follows: If you live in Europe I suggest you investigate the ISDN card section. If you are planning to use ISDN primarily to connect to the Internet with an Internet Provider on a dial-up non-dedicated basis, I suggest you look into Terminal Adapters. This will give you the most flexibility, with the fewest problems, if you change providers. If you are connecting two LANs together, or connecting to the Internet with a dedicated ISDN connection, I suggest you consider the stand alone router/bridge option. Cost is a significant factor in determining what solution you will choose. The following options are listed from least expensive to most expensive. ISDN Cards Contributed by &a.hm;. This section is really only relevant to ISDN users in countries where the DSS1/Q.931 ISDN standard is supported. Some growing number of PC ISDN cards are supported under FreeBSD 2.2.x and up by the isdn4bsd driver package. It is still under development but the reports show that it is successfully used all over Europe. The latest isdn4bsd version is available from ftp://isdn4bsd@ftp.consol.de/pub/, the main isdn4bsd ftp site (you have to log in as user isdn4bsd , give your mail address as the password and change to the pub directory. Anonymous ftp as user ftp or anonymous will not give the desired result). Isdn4bsd allows you to connect to other ISDN routers using either IP over raw HDLC or by using synchronous PPP. A telephone answering machine application is also available. Many ISDN PC cards are supported, mostly the ones with a Siemens ISDN chipset (ISAC/HSCX), support for other chipsets (from Motorola, Cologne Chip Designs) is currently under development. For an up-to-date list of supported cards, please have a look at the README file. In case you are interested in adding support for a different ISDN protocol, a currently unsupported ISDN PC card or otherwise enhancing isdn4bsd, please get in touch with hm@kts.org. A majordomo maintained mailing list is available. To join the list, send mail to &a.majordomo; and specify: subscribe freebsd-isdn in the body of your message. ISDN Terminal Adapters Terminal adapters(TA), are to ISDN what modems are to regular phone lines. Most TA's use the standard hayes modem AT command set, and can be used as a drop in replacement for a modem. A TA will operate basically the same as a modem except connection and throughput speeds will be much faster than your old modem. You will need to configure PPP exactly the same as for a modem setup. Make sure you set your serial speed as high as possible. The main advantage of using a TA to connect to an Internet Provider is that you can do Dynamic PPP. As IP address space becomes more and more scarce, most providers are not willing to provide you with a static IP anymore. Most stand-alone routers are not able to accommodate dynamic IP allocation. TA's completely rely on the PPP daemon that you are running for their features and stability of connection. This allows you to upgrade easily from using a modem to ISDN on a FreeBSD machine, if you already have PPP setup. However, at the same time any problems you experienced with the PPP program and are going to persist. If you want maximum stability, use the kernel PPP option, not the user-land iijPPP. The following TA's are know to work with FreeBSD. Motorola BitSurfer and Bitsurfer Pro Adtran Most other TA's will probably work as well, TA vendors try to make sure their product can accept most of the standard modem AT command set. The real problem with external TA's is like modems you need a good serial card in your computer. You should read the serial ports section in the handbook for a detailed understanding of serial devices, and the differences between asynchronous and synchronous serial ports. A TA running off a standard PC serial port (asynchronous) limits you to 115.2Kbs, even though you have a 128Kbs connection. To fully utilize the 128Kbs that ISDN is capable of, you must move the TA to a synchronous serial card. Do not be fooled into buying an internal TA and thinking you have avoided the synchronous/asynchronous issue. Internal TA's simply have a standard PC serial port chip built into them. All this will do, is save you having to buy another serial cable, and find another empty electrical socket. A synchronous card with a TA is at least as fast as a stand-alone router, and with a simple 386 FreeBSD box driving it, probably more flexible. The choice of sync/TA v.s. stand-alone router is largely a religious issue. There has been some discussion of this in the mailing lists. I suggest you search the archives for the complete discussion. Stand-alone ISDN Bridges/Routers ISDN bridges or routers are not at all specific to FreeBSD or any other operating system. For a more complete description of routing and bridging technology, please refer to a Networking reference book. In the context of this page, I will use router and bridge interchangeably. As the cost of low end ISDN routers/bridges comes down, it will likely become a more and more popular choice. An ISDN router is a small box that plugs directly into your local Ethernet network(or card), and manages its own connection to the other bridge/router. It has all the software to do PPP and other protocols built in. A router will allow you much faster throughput that a standard TA, since it will be using a full synchronous ISDN connection. The main problem with ISDN routers and bridges is that interoperability between manufacturers can still be a problem. If you are planning to connect to an Internet provider, I recommend that you discuss your needs with them. If you are planning to connect two lan segments together, ie: home lan to the office lan, this is the simplest lowest maintenance solution. Since you are buying the equipment for both sides of the connection you can be assured that the link will work. For example to connect a home computer or branch office network to a head office network the following setup could be used. Branch office or Home network Network is 10 Base T Ethernet. Connect router to network cable with AUI/10BT transceiver, if necessary. ---Sun workstation | ---FreeBSD box | ---Windows 95 (Do not admit to owning it) | Stand-alone router | ISDN BRI line If your home/branch office is only one computer you can use a twisted pair crossover cable to connect to the stand-alone router directly. Head office or other lan Network is Twisted Pair Ethernet. -------Novell Server | H | | ---Sun | | | U ---FreeBSD | | | ---Windows 95 | B | |___---Stand-alone router | ISDN BRI line One large advantage of most routers/bridges is that they allow you to have 2 separate independent PPP connections to 2 separate sites at the same time. This is not supported on most TA's, except for specific(expensive) models that have two serial ports. Do not confuse this with channel bonding, MPP etc. This can be very useful feature, for example if you have an dedicated ISDN connection at your office and would like to tap into it, but don't want to get another ISDN line at work. A router at the office location can manage a dedicated B channel connection (64Kbs) to the internet, as well as a use the other B channel for a separate data connection. The second B channel can be used for dial-in, dial-out or dynamically bond(MPP etc.) with the first B channel for more bandwidth. An Ethernet bridge will also allow you to transmit more than just IP traffic, you can also send IPX/SPX or whatever other protocols you use. NIS/YP Written by &a.unfurl;, 21 January 2000, enhanced with parts and comments from Eric Ogren eogren@earthlink.net and Udo Erdelhoff ue@nathan.ruhr.de in June 2000. What is it? NIS, which stands for Network Information Services, was developed by Sun Microsystems to centralize administration of Unix (originally SunOS) systems. It has now essentially become an industry standard; all major Unices (Solaris, HP-UX, AIX, Linux, NetBSD, OpenBSD, FreeBSD, etc) support NIS. NIS was formerly known as Yellow Pages (or yp), but due to copyright violations, Sun was forced to change the name. It is a RPC-based client/server system that allows a group of machines within an NIS domain to share a common set of configuration files. This permits a system administrator to set up NIS client systems with only minimal configuration data and add, remove or modify configuration data from a single location. It is similar to Windows NT's domain system; although the internal implementation of the two aren't at all similar, the basic functionality can be compared. Terms/processes you should know There are several terms and several important user processes that you will come across when attempting to implement NIS on FreeBSD, whether you are trying to create an NIS server or act an NIS client: The NIS domainname. An NIS master server and all of its clients (including its slave servers) have a NIS domainname. Similar to an NT domain name, the NIS domainname does not have anything to do with DNS. portmap. portmap must be running in order to enable RPC (Remote Procedure Call, a network protocol used by NIS). If portmap is not running, it will be impossible to run an NIS server, or to act as an NIS client. ypbind. ypbind “binds” an NIS client to its NIS server. It will take the NIS domainname from the system, and using RPC, connect to the server. ypbind is the core of client-server communication in an NIS environment; if ypbind dies on a client machine, it will not be able to access the NIS server. ypserv. ypserv, which should only be running on NIS servers, is the NIS server process itself. If ypserv dies, then the server will no longer be able to respond to NIS requests (hopefully, there is a slave server to take over for it). There are some implementations of NIS (but not the FreeBSD one), that don't try to reconnect to another server if the server it used before dies. Often, the only thing that helps in this case is to restart the server process (or even the whole server) or the ypbind process on the client. rpc.yppasswdd. rpc.yppasswdd, another process that should only be running on NIS master servers, is a daemon that will allow NIS clients to change their NIS passwords. If this daemon is not running, users will have to login to the NIS master server and change their passwords there. How does it work? There are three types of hosts in an NIS environment; master servers, slave servers, and clients. Servers act as a central repository for host configuration information. Master servers hold the authoritative copy of this information, while slave servers mirror this information for redundancy. Clients rely on the servers to provide this information to them. Information in many files can be shared in this manner. The master.passwd, group, and hosts files are commonly shared via NIS. Whenever a process on a client needs information that would normally be found in these files locally, it makes a query to the server it is bound to, to get this information. Machine types A NIS master server. This server, analogous to a Windows NT primary domain controller, maintains the files used by all of the NIS clients. The passwd, group, and other various files used by the NIS clients live on the master server. It is possible for one machine to be an NIS master server for more than one NIS domain. However, this will not be covered in this introduction, which assumes a relatively small-scale NIS environment. NIS slave servers. Similar to NT's backup domain controllers, NIS slave servers maintain copies of the NIS master's data files. NIS slave servers provide the redundancy, which is needed in important environments. They also help to balance the load of the master server: NIS Clients always attach to the NIS server, whose response they get first, and this includes slave-server-replies. NIS clients. NIS clients, like most NT workstations, authenticate against the NIS server (or the NT domain controller in the NT Workstation case) to log on. Using NIS/YP This section will deal with setting up a sample NIS environment. This section assumes that you are running FreeBSD 3.3 or later. The instructions given here will probably work for any version of FreeBSD greater than 3.0, but there are no guarantees that this is true. Planning Let's assume that you are the administrator of a small university lab. This lab, which consists of 15 FreeBSD machines, currently has no centralized point of administration; each machine has its own /etc/passwd and /etc/master.passwd. These files are kept in sync with each other only through manual intervention; currently, when you add a user to the lab, you must run adduser on all 15 machines. Clearly, this has to change, so you have decided to convert the lab to use NIS, using two of the machines as servers. Therefore, the configuration of the lab now looks something like: Machine name IP address Machine role ellington 10.0.0.2 NIS master coltrane 10.0.0.3 NIS slave basie 10.0.0.4 Faculty workstation bird 10.0.0.5 Client machine cli[1-11] 10.0.0.[6-17] Other client machines If you are setting up a NIS scheme for the first time, it is a good idea to think through how you want to go about it. No matter what the size of your network, there are a few decisions that need to be made. Choosing a NIS Domain Name This might not be the domainname that you are used to. It is more accurately called the NIS domainname. When a client broadcasts its requests for info, it includes the name of the NIS domain that it is part of. This is how multiple servers on one network can tell which server should answer which request. Think of the NIS domainname as the name for a group of hosts that are related in someway way. Some organizations choose to use their Internet domainname for their NIS domainname. This is not recommended as it can cause confusion when trying to debug network problems. The NIS domainname should be unique within your network and it is helpful if it describes the group of machines it represents. For example, the Art department at Acme Inc. might be in the "acme-art" NIS domain. For this example, assume you have chosen the name test-domain. However, some operating systems (notably SunOS) use their NIS domain name as their Internet domain name. If one or more machines on your network have this restriction, you must use the Internet domain name as your NIS domain name. Physical Server Requirements There are several things to keep in mind when choosing a machine to use as a NIS server. One of the unfortunate things about NIS is the level of dependency the clients have on the server. If a client cannot contact the server for its NIS domain, very often the machine becomes unusable. The lack of user and group information causes most systems to temporarily freeze up. With this in mind you should make sure to choose a machine that won't be prone to being rebooted regularly, or one that might be used for development. The NIS server should ideally be a stand alone machine whose sole purpose in life is to be an NIS server. If you have a network that is not very heavily used, it is acceptable to put the NIS server on a machine running other services, just keep in mind that if the NIS server becomes unavailable, it will affect all of your NIS clients adversely. NIS Servers The canonical copies of all NIS information are stored on a single machine called the NIS master server. The databases used to store the information are called NIS maps. In FreeBSD, these maps are stored in /var/yp/[domainname] where [domainname] is the name of the NIS domain being served. A single NIS server can support several domains at once, therefore it is possible to have several such directories, one for each supported domain. Each domain will have its own independent set of maps. NIS master and slave servers handle all NIS requests with the ypserv daemon. Ypserv is responsible for receiving incoming requests from NIS clients, translating the requested domain and map name to a path to the corresponding database file and transmitting data from the database back to the client. Setting up a NIS master server Setting up a master NIS server can be relatively straight forward, depending on your needs. FreeBSD comes with support for NIS out-of-the-box. All you need is to add the following lines to /etc/rc.conf, and FreeBSD will do the rest for you. nisdomainname="test-domain" This line will set the NIS domainname to test-domain upon network setup (e.g. after reboot). nis_server_enable="YES" This will tell FreeBSD to start up the NIS server processes when the networking is next brought up. nis_yppasswdd_enable="YES" This will enable the rpc.yppasswdd daemon, which, as mentioned above, will allow users to change their NIS password from a client machine. Now, everything you have to do is to run the command /etc/netstart as superuser. It will setup everything for you, using the values you defined in /etc/rc.conf. Initializing the NIS maps The NIS maps are database files, that are kept in the /var/yp directory. They are generated from configuration files in the /etc directory of the NIS master, with one exception: the /etc/master.passwd file. This is for a good reason; you don't want to propagate passwords to your root and other administrative accounts to all the servers in the NIS domain. Therefore, before we initialize the NIS maps, you should: &prompt.root; cp /etc/master.passwd /var/yp/master.passwd &prompt.root; cd /var/yp &prompt.root; vi master.passwd You should remove all entries regarding system accounts (bin, tty, kmem, games, etc), as well as any accounts that you don't want to be propagated to the NIS clients (for example root and any other UID 0 (superuser) accounts). Make sure the /var/yp/master.passwd is neither group nor world readable (mode 600)! Use the chmod command, if appropriate. When you have finished, it's time to initialize the NIS maps! FreeBSD includes a script named ypinit to do this for you (see its man page for more information). Note that this script is available on most UNIX OSs, but not on all. On Digital Unix/Compaq Tru64 Unix it is called ypsetup. Because we are generating maps for an NIS master, we are going to pass the option to ypinit. To generate the NIS maps, assuming you already performed the steps above, run: ellington&prompt.root; ypinit -m test-domain Server Type: MASTER Domain: test-domain Creating an YP server will require that you answer a few questions. Questions will all be asked at the beginning of the procedure. Do you want this procedure to quit on non-fatal errors? [y/n: n] n Ok, please remember to go back and redo manually whatever fails. If you don't, something might not work. At this point, we have to construct a list of this domains YP servers. rod.darktech.org is already known as master server. Please continue to add any slave servers, one per line. When you are done with the list, type a <control D>. master server : ellington next host to add: coltrane next host to add: ^D The current list of NIS servers looks like this: ellington coltrane Is this correct? [y/n: y] y [..output from map generation..] NIS Map update completed. ellington has been setup as an YP master server without any errors. ypinit should have created /var/yp/Makefile from /var/yp/Makefile.dist. When created, this file assumes that you are operating in a single server NIS environment with only FreeBSD machines. Since test-domain has a slave server as well, you must edit /var/yp/Makefile: ellington&prompt.root; vi /var/yp/Makefile You should comment out the line that says `NOPUSH = "True"' (if it is not commented out already). Setting up a NIS slave server Setting up an NIS slave server is even more simple than setting up the master. Log on to the slave server and edit the file /etc/rc.conf as you did before. The only difference is that we now must use the option when running ypinit. The option requires the name of the NIS master be passed to it as well, so our command line looks like: coltrane&prompt.root; ypinit -s ellington test-domain Server Type: SLAVE Domain: test-domain Master: ellington Creating an YP server will require that you answer a few questions. Questions will all be asked at the beginning of the procedure. Do you want this procedure to quit on non-fatal errors? [y/n: n] n Ok, please remember to go back and redo manually whatever fails. If you don't, something might not work. There will be no further questions. The remainder of the procedure should take a few minutes, to copy the databases from ellington. Transferring netgroup... ypxfr: Exiting: Map successfully transferred Transferring netgroup.byuser... ypxfr: Exiting: Map successfully transferred Transferring netgroup.byhost... ypxfr: Exiting: Map successfully transferred Transferring master.passwd.byuid... ypxfr: Exiting: Map successfully transferred Transferring passwd.byuid... ypxfr: Exiting: Map successfully transferred Transferring passwd.byname... ypxfr: Exiting: Map successfully transferred Transferring group.bygid... ypxfr: Exiting: Map successfully transferred Transferring group.byname... ypxfr: Exiting: Map successfully transferred Transferring services.byname... ypxfr: Exiting: Map successfully transferred Transferring rpc.bynumber... ypxfr: Exiting: Map successfully transferred Transferring rpc.byname... ypxfr: Exiting: Map successfully transferred Transferring protocols.byname... ypxfr: Exiting: Map successfully transferred Transferring master.passwd.byname... ypxfr: Exiting: Map successfully transferred Transferring networks.byname... ypxfr: Exiting: Map successfully transferred Transferring networks.byaddr... ypxfr: Exiting: Map successfully transferred Transferring netid.byname... ypxfr: Exiting: Map successfully transferred Transferring hosts.byaddr... ypxfr: Exiting: Map successfully transferred Transferring protocols.bynumber... ypxfr: Exiting: Map successfully transferred Transferring ypservers... ypxfr: Exiting: Map successfully transferred Transferring hosts.byname... ypxfr: Exiting: Map successfully transferred coltrane has been setup as an YP slave server without any errors. Don't forget to update map ypservers on ellington. You should now have a directory called /var/yp/test-domain. Copies of the NIS master server's maps should be in this directory. You will need to make sure that these stay updated. The following /etc/crontab entries on your slave servers should do the job: 20 * * * * root /usr/libexec/ypxfr passwd.byname 21 * * * * root /usr/libexec/ypxfr passwd.byuid These two lines force the slave to sync its maps with the maps on the master server. Although this is not mandatory, because the master server tries to make sure any changes to it's NIS maps are communicated to it's slaves, the password information is so vital to systems that depend on the server, that it is a good idea to force the updates. This is more important on busy networks where map updates might not always complete. Now, run the command /etc/netstart on the slave server as well, which again starts the NIS server. NIS Clients An NIS client establishes what is called a binding to a particular NIS server using the ypbind daemon. ypbind checks the system's default domain (as set by the domainname command), and begins broadcasting RPC requests on the local network. These requests specify the name of the domain for which ypbind is attempting to establish a binding. If a server that has been configured to serve the requested domain receives one of the broadcasts, it will respond to ypbind, which will record the server's address. If there are several servers available (a master and several slaves, for example), ypbind will use the address of the first one to respond. From that point on, the client system will direct all of its NIS requests to that server. Ypbind will occasionally ping the server to make sure it is still up and running. If it fails to receive a reply to one of its pings within a reasonable amount of time, ypbind will mark the domain as unbound and begin broadcasting again in the hopes of locating another server. Setting up an NIS client Setting up a FreeBSD machine to be a NIS client is fairly straight forward. Edit the file /etc/rc.conf and add the following lines in order to set the NIS domainname and start ypbind upon network startup: nisdomainname="test-domain" nis_client_enable="YES" To import all possible password entries from the NIS server, add this line to your /etc/master.passwd file, using vipw: +::::::::: This line will afford anyone with a valid account in the NIS server's password maps an account. There are many ways to configure your NIS client by changing this line. See the netgroups part below for more information. For more detailed reading see O'Reilly's book on Managing NFS and NIS. To import all possible group entries from the NIS server, add this line to your /etc/group file: +:*:: After completing these steps, you should be able to run ypcat passwd and see the NIS server's passwd map. NIS Security In general, any remote user can issue an RPC to ypserv and retrieve the contents of your NIS maps, provided the remote user knows your domainname. To prevent such unauthorized transactions, ypserv supports a feature called securenets which can be used to restrict access to a given set of hosts. At startup, ypserv will attempt to load the securenets information from a file called /var/yp/securenets. This path varies depending on the path specified with the option. This file contains entries that consist of a network specification and a network mask separated by white space. Lines starting with # are considered to be comments. A sample securenets file might look like this: # allow connections from local host -- mandatory 127.0.0.1 255.255.255.255 # allow connections from any host # on the 192.168.128.0 network 192.168.128.0 255.255.255.0 # allow connections from any host # between 10.0.0.0 to 10.0.15.255 # this includes the machines in the testlab 10.0.0.0 255.255.240.0 If ypserv receives a request from an address that matches one of these rules, it will process the request normally. If the address fails to match a rule, the request will be ignored and a warning message will be logged. If the /var/yp/securenets file does not exist, ypserv will allow connections from any host. The ypserv program also has support for Wietse Venema's tcpwrapper package. This allows the administrator to use the tcpwrapper configuration files for access control instead of /var/yp/securenets. While both of these access control mechanisms provide some security, they, like the privileged port test, are vulnerable to IP spoofing attacks. All NIS-related traffic should be blocked at your firewall. Servers using /var/yp/securenets may fail to serve legitimate NIS clients with archaic TCP/IP implementations. Some of these implementations set all host bits to zero when doing broadcasts and/or fail to observe the subnet mask when calculating the broadcast address. While some of these problems can be fixed by changing the client configuration, other problems may force the retirement of the client systems in question or the abandonment of /var/yp/securenets. Using /var/yp/securenets on a server with such an archaic implementation of TCP/IP is a really bad idea and will lead to loss of NIS functionality for large parts of your network. The use of the tcpwrapper package increases the latency of your NIS server. The additional delay may be long enough to cause timeouts in client programs, especially in busy networks or with slow NIS servers. If one or more of your client systems suffers from these symptoms, you should convert the client systems in question into NIS slave servers and force them to bind to themselves. Barring some users from logging on In our lab, there is a machine basie that is supposed to be a faculty only workstation. We don't want to take this machine out of the NIS domain, yet the passwd file on the master NIS server contains accounts for both faculty and students. What can we do? There is a way to bar specific users from logging on to a machine, even if they are present in the NIS database. To do this, all you must do is add -username to the end of the /etc/master.passwd file on the client machine, where username is the username of the user you wish to bar from logging in. This should preferably be done using vipw, since vipw will sanity check your changes to /etc/master.passwd, as well as automatically rebuild the password database when you finish editing. For example, if we wanted to bar user bill from logging on to basie we would: basie&prompt.root; vipw [add -bill to the end, exit] vipw: rebuilding the database... vipw: done basie&prompt.root; cat /etc/master.passwd root:[password]:0:0::0:0:The super-user:/root:/bin/csh toor:[password]:0:0::0:0:The other super-user:/root:/bin/sh daemon:*:1:1::0:0:Owner of many system processes:/root:/sbin/nologin operator:*:2:5::0:0:System &:/:/sbin/nologin bin:*:3:7::0:0:Binaries Commands and Source,,,:/:/sbin/nologin tty:*:4:65533::0:0:Tty Sandbox:/:/sbin/nologin kmem:*:5:65533::0:0:KMem Sandbox:/:/sbin/nologin games:*:7:13::0:0:Games pseudo-user:/usr/games:/sbin/nologin news:*:8:8::0:0:News Subsystem:/:/sbin/nologin man:*:9:9::0:0:Mister Man Pages:/usr/share/man:/sbin/nologin bind:*:53:53::0:0:Bind Sandbox:/:/sbin/nologin uucp:*:66:66::0:0:UUCP pseudo-user:/var/spool/uucppublic:/usr/libexec/uucp/uucico xten:*:67:67::0:0:X-10 daemon:/usr/local/xten:/sbin/nologin pop:*:68:6::0:0:Post Office Owner:/nonexistent:/sbin/nologin nobody:*:65534:65534::0:0:Unprivileged user:/nonexistent:/sbin/nologin +::::::::: -bill basie&prompt.root; Using netgroups The netgroups part was contributed by Udo Erdelhoff ue@nathan.ruhr.de in July 2000. The method shown in the previous chapter works reasonably well if you need special rules for a very small number of users and/or machines. On larger networks, you will forget to bar some users from logging onto sensitive machines, or you may even have to modify each machine separately, thus loosing the main benefit of NIS, centralized administration. The NIS developers' solution for this problem is called netgroups. Their purpose and semantics can be compared to the normal groups used by Unix file systems. The main differences are the lack of a numeric id and the ability to define a netgroup by including both user accounts and other netgroups. Netgroups were developed to handle large, complex networks with hundreds of users and machines. On one hand, this is a Good Thing if you are forced to deal with such a situation. On the other hand, this complexity makes it almost impossible to explain netgroups with really simple examples. The example used in the remainder of this chapter demonstrates this problem. Let us assume that your successful introduction of NIS in your laboratory caught your superiors' interest. Your next job is to extend your NIS domain to cover some of the other machines on campus. The two tables contain the names of the new users and new machines as well as brief descriptions of them. User Name(s) Description alpha, beta Normal employees of the IT department charlie, delta The new apprentices of the IT department echo, foxtrott, golf, ... Ordinary employees able, baker, ... The current interns Machine Name(s) Description war, death, famine, pollution Your most important servers. Only the IT employees are allowed to log onto these machines. pride, greed, envy, wraith, lust, sloth Less important servers. All members of the IT department are allowed to login onto these machines. one, two, three, four, ... Ordinary workstations. Only the real employees are allowed to use these machines. trashcan A very old machine without any critical data. Even the intern is allowed to use this box. If you tried to implement these restrictions by separately blocking each user, you would have to add one -user line to each system's passwd for each user who is not allowed to login onto that system. If you forget just one entry, you could be in trouble. It may feasible to do this correctly during the initial setup, however you will eventually forget to add the lines for new users during day-to-day operations. After all, Murphy was an optimist. Handling this situation with netgroups offers several advantages. Each user need not be handled separately; you assign a user to one or netgroup and allow or forbid logins for all members of the netgroup. If you add a new machine, you will only have to define login restrictions for netgroups. If a new user is added, you will only have to add the user to one or more netgroups. Those changes are independent of each other; no more for each combination of user and machine do... If your NIS setup is planned carefully, you will only have to modify exactly one central configuration file to grant or deny access to machines. The first step is the initialization of the NIS map netgroup. FreeBSD's ypinit does not create this map by default, but its NIS implementation will support it once it has been created. To create an empty map, simply type ellington&prompt.root; vi /var/yp/netgroup and start adding content. For our example, we need at least four netgroups: IT employees, IT apprentices, normal employees and interns. IT_EMP (,alpha,test-domain) (,beta,test-domain) IT_APP (,charlie,test-domain) (,delta,test-domain) USERS (,echo,test-domain) (,foxtrott,test-domain) \ (,golf,test-domain) INTERNS (,able,test-domain) (,baker,test-domain) IT_EMP, IT_APP etc. are the names of the netgroups. Each bracketed group adds one or more user accounts to it. The three fields inside a group are: The name of the host(s) where the following items are valid. If you do not specify a hostname, the entry is valid on all hosts. If you do specify a hostname, you will a realm of darkness, horror and utter confusion. The name of the account that belongs to this netgroup. The NIS domain for the account. You can import accounts from other NIS domains into your netgroup if you are one of unlucky fellows with more than one NIS domain. Each of these fields can contain wildcards. See &man.netgroup.5; for details. Netgroup names longer than 8 characters should not be used, especially if you have machines running other operating systems within your NIS domain. The names are case sensitive; using capital letters for your netgroup names is an easy way to distinguish between user, machine and netgroup names. Some NIS clients (other than FreeBSD) cannot handle netgroups with a large number of entries. For example, some older versions of SunOS start to cause trouble if a netgroup contains more than 15 entries. You can circumvent this limit by creating several sub-netgroups with 15 users or less and a real netgroup that consists of the sub-netgroups: BIGGRP1 (,joe1,domain) (,joe2,domain) (,joe3,domain) [...] BIGGRP2 (,joe16,domain) (,joe17,domain) [...] BIGGRP3 (,joe32,domain) (,joe33,domain) BIGGROUP BIGGRP1 BIGGRP2 BIGGRP3 You can repeat this process if you need more than 225 users within a single netgroup. Activating and distributing your new NIS map is easy: ellington&prompt.root; cd /var/yp ellington&prompt.root; make This will generate the three NIS maps netgroup, netgroup.byhost and netgroup.byuser. Use &man.ypcat.1; to check if your new NIS map are available: ellington&prompt.user; ypcat -k netgroup ellington&prompt.user; ypcat -k netgroup.byhost ellington&prompt.user; ypcat -k netgroup.byuser The output of the first command should resemble the contents of /var/yp/netgroup. The second command will not produce output if you have not specified host-specific netgroups. The third command can be used to get the list of netgroups for a user. The client setup is quite simple. To configure the server war, you only have to start &man.vipw.8; and replace the line +::::::::: with +@IT_EMP::::::::: Now, only the data for the users defined in the netgroup IT_EMP is imported into war's password database and only these users are allowed to login. Unfortunately, this limitation also applies to the ~ function of the shell and all routines converting between user names and numerical user ids. In other words, cd ~user will not work, ls -l will show the numerical id instead of the username and find . -user joe -print will fail with No such user. To fix this, you will have to import all user entries without allowing them to login onto your servers. This can be achieved by adding another line to /etc/master.passwd. This line should contain +:::::::::/sbin/nologin, meaning Import all entries but replace the shell with /sbin/nologin in the imported entries. You can replace any field in the passwd entry by placing a default value in your /etc/master.passwd. Make sure that the line +:::::::::/sbin/nologin is placed after +@IT_EMP:::::::::. Otherwise, all user accounts imported from NIS will have /sbin/nologin as their login shell. After this change, you will only have to change one NIS map if a new employee joins the IT department. You could use a similar approach for the less important servers by replacing the old +::::::::: in their local version of /etc/master.passwd with something like this: +@IT_EMP::::::::: +@IT_APP::::::::: +:::::::::/sbin/nologin The corresponding lines for the normal workstations could be: +@IT_EMP::::::::: +@USERS::::::::: +:::::::::/sbin/nologin And everything would be fine until there is a policy change a few weeks later: The IT department starts hiring interns. The IT interns are allowed to use the normal workstations and the less important servers; and the IT apprentices are allowed to login onto the main servers. You add a new netgroup IT_INTERN, add the new IT interns to this netgroup and start to change the config on each and every machine... As the old saying goes: Errors in centralized planning lead to global mess. NIS' ability to create netgroups from other netgroups can be used to prevent situations like these. One possibility is the creation of role-based netgroups. For example, you could create a netgroup called BIGSRV to define the login restrictions for the important servers, another netgroup called SMALLSRV for the less important servers and a third netgroup called USERBOX for the normal workstations. Each of these netgroups contains the netgroups that are allowed to login onto these machines. The new entries for your NIS map netgroup should look like this: BIGSRV IT_EMP IT_APP SMALLSRV IT_EMP IT_APP ITINTERN USERBOX IT_EMP ITINTERN USERS This method of defining login restrictions works reasonably well if you can define groups of machines with identical restrictions. Unfortunately, this is the exception and not the rule. Most of the time, you will need the ability to define login restrictions on a per-machine basis. Machine-specific netgroup definitions are the other possibility to deal with the policy change outlined above. In this scenario, the /etc/master.passwd of each box contains two lines starting with ``+''. The first of them adds a netgroup with the accounts allowed to login onto this machine, the second one adds all other accounts with /sbin/nologin as shell. It is a good idea to use the ALL-CAPS version of the machine name as the name of the netgroup. In other words, the lines should look like this: +@BOXNAME::::::::: +:::::::::/sbin/nologin Once you have completed this task for all your machines, you will not have to modify the local versions of /etc/master.passwd ever again. All further changes can be handled by modifying the NIS map. Here is an example of a possible netgroup map for this scenario with some additional goodies. # Define groups of users first IT_EMP (,alpha,test-domain) (,beta,test-domain) IT_APP (,charlie,test-domain) (,delta,test-domain) DEPT1 (,echo,test-domain) (,foxtrott,test-domain) DEPT2 (,golf,test-domain) (,hotel,test-domain) DEPT3 (,india,test-domain) (,juliet,test-domain) ITINTERN (,kilo,test-domain) (,lima,test-domain) D_INTERNS (,able,test-domain) (,baker,test-domain) # # Now, define some groups based on roles USERS DEPT1 DEPT2 DEPT3 BIGSRV IT_EMP IT_APP SMALLSRV IT_EMP IT_APP ITINTERN USERBOX IT_EMP ITINTERN USERS # # And a groups for a special tasks # Allow echo and golf to access our anti-virus-machine SECURITY IT_EMP (,echo,test-domain) (,golf,test-domain) # # machine-based netgroups # Our main servers WAR BIGSRV FAMINE BIGSRV # User india needs access to this server POLLUTION BIGSRV (,india,test-domain) # # This one is really important and needs more access restrictions DEATH IT_EMP # # The anti-virus-machine mentioned above ONE SECURITY # # Restrict a machine to a single user TWO (,hotel,test-domain) # [...more groups to follow] If you are using some kind of database to manage your user accounts, you should be able to create the first part of the map with your database's report tools. This way, new users will automatically have access to the boxes. One last word of caution: It may not always be advisable to use machine-based netgroups. If you are deploying a couple dozen or even hundreds of identical machines for student labs, you should use role-based netgroups instead of machine-based netgroups to keep the size of the NIS map within reasonable limits. Important things to remember There are still a couple of things that you will need to do differently now that you are in an NIS environment. Every time you wish to add a user to the lab, you must add it to the master NIS server only, and you must remember to rebuild the NIS maps. If you forget to do this, the new user will not be able to login anywhere except on the NIS master. For example, if we needed to add a new user “jsmith” to the lab, we would: &prompt.root; pw useradd jsmith &prompt.root; cd /var/yp &prompt.root; make test-domain You could also run adduser jsmith instead of pw useradd jsmith. Keep the administration accounts out of the NIS maps. You don't want to be propagating administrative accounts and passwords to machines that will have users that shouldn't have access to those accounts. Keep the NIS master and slave secure, and minimize their downtime. If somebody either hacks or simply turns off these machines, they have effectively rendered many people without the ability to login to the lab. This is the chief weakness of any centralized administration system, and it is probably the most important weakness. If you do not protect your NIS servers, you will have a lot of angry users! NIS v1 compatibility FreeBSD's ypserv has some support for serving NIS v1 clients. FreeBSD's NIS implementation only uses the NIS v2 protocol, however other implementations include support for the v1 protocol for backwards compatibility with older systems. The ypbind daemons supplied with these systems will try to establish a binding to an NIS v1 server even though they may never actually need it (and they may persist in broadcasting in search of one even after they receive a response from a v2 server). Note that while support for normal client calls is provided, this version of ypserv does not handle v1 map transfer requests; consequently, it can not be used as a master or slave in conjunction with older NIS servers that only support the v1 protocol. Fortunately, there probably are not any such servers still in use today. NIS servers that are also NIS clients Care must be taken when running ypserv in a multi-server domain where the server machines are also NIS clients. It is generally a good idea to force the servers to bind to themselves rather than allowing them to broadcast bind requests and possibly become bound to each other. Strange failure modes can result if one server goes down and others are dependent upon on it. Eventually all the clients will time out and attempt to bind to other servers, but the delay involved can be considerable and the failure mode is still present since the servers might bind to each other all over again. You can force a host to bind to a particular server by running ypbind with the flag. libscrypt v.s. libdescrypt One of the most common issues that people run into when trying to implement NIS is crypt library compatibility. If your NIS server is using the DES crypt libraries, it will only support clients that are using DES as well. To check which one your server and clients are using look at the symlinks in /usr/lib. If the machine is configured to use the DES libraries, it will look something like this: &prompt.user; ls -l /usr/lib/*crypt* lrwxrwxrwx 1 root wheel 13 Jul 15 08:55 /usr/lib/libcrypt.a@ -> libdescrypt.a lrwxrwxrwx 1 root wheel 14 Jul 15 08:55 /usr/lib/libcrypt.so@ -> libdescrypt.so lrwxrwxrwx 1 root wheel 16 Jul 15 08:55 /usr/lib/libcrypt.so.2@ -> libdescrypt.so.2 lrwxrwxrwx 1 root wheel 15 Jul 15 08:55 /usr/lib/libcrypt_p.a@ -> libdescrypt_p.a -r--r--r-- 1 root wheel 13018 Nov 8 14:27 /usr/lib/libdescrypt.a lrwxr-xr-x 1 root wheel 16 Nov 8 14:27 /usr/lib/libdescrypt.so@ -> libdescrypt.so.2 -r--r--r-- 1 root wheel 12965 Nov 8 14:27 /usr/lib/libdescrypt.so.2 -r--r--r-- 1 root wheel 14750 Nov 8 14:27 /usr/lib/libdescrypt_p.a If the machine is configured to use the standard FreeBSD MD5 crypt libraries they will look something like this: &prompt.user; ls -l /usr/lib/*crypt* lrwxrwxrwx 1 root wheel 13 Jul 15 08:55 /usr/lib/libcrypt.a@ -> libscrypt.a lrwxrwxrwx 1 root wheel 14 Jul 15 08:55 /usr/lib/libcrypt.so@ -> libscrypt.so lrwxrwxrwx 1 root wheel 16 Jul 15 08:55 /usr/lib/libcrypt.so.2@ -> libscrypt.so.2 lrwxrwxrwx 1 root wheel 15 Jul 15 08:55 /usr/lib/libcrypt_p.a@ -> libscrypt_p.a -r--r--r-- 1 root wheel 6194 Nov 8 14:27 /usr/lib/libscrypt.a lrwxr-xr-x 1 root wheel 14 Nov 8 14:27 /usr/lib/libscrypt.so@ -> libscrypt.so.2 -r--r--r-- 1 root wheel 7579 Nov 8 14:27 /usr/lib/libscrypt.so.2 -r--r--r-- 1 root wheel 6684 Nov 8 14:27 /usr/lib/libscrypt_p.a If you have trouble authenticating on an NIS client, this is a pretty good place to start looking for possible problems. If you want to deploy an NIS server for a heterogenous network, you will probably have to use DES on all systems because it is the lowest common standard. DHCP Written by &a.gsutter;, March 2000. What is DHCP? DHCP, the Dynamic Host Configuration Protocol, describes the means by which a system can connect to a network and obtain the necessary information for communication upon that network. FreeBSD uses the ISC (Internet Software Consortium) DHCP implementation, so all implementation-specific information here is for use with the ISC distribution. What This Section Covers This handbook section attempts to describe only the parts of the DHCP system that are integrated with FreeBSD; consequently, the server portions are not described. The DHCP manual pages, in addition to the references below, are useful resources. How it Works When dhclient, the DHCP client, is executed on the client machine, it begins broadcasting requests for configuration information. By default, these requests are on UDP port 68. The server replies on UDP 67, giving the client an IP address and other relevant network information such as netmask, router, and DNS servers. All of this information comes in the form of a DHCP "lease" and is only valid for a certain time (configured by the DHCP server maintainer). In this manner, stale IP addresses for clients no longer connected to the network can be automatically reclaimed. DHCP clients can obtain a great deal of information from the server. An exhaustive list may be found in &man.dhcp-options.5;. FreeBSD Integration FreeBSD fully integrates the ISC DHCP client, dhclient. DHCP client support is provided within both the installer and the base system, obviating the need for detailed knowledge of network configurations on any network that runs a DHCP server. dhclient has been included in all FreeBSD distributions since 3.2. DHCP is supported by sysinstall. When configuring a network interface within sysinstall, the first question asked is, "Do you want to try dhcp configuration of this interface?" Answering affirmatively will execute dhclient, and if successful, will fill in the network configuration information automatically. There are two things you must do to have your system use DHCP upon startup: Make sure that the bpf device is compiled into your kernel. To do this, add pseudo-device bpf to your kernel configuration file, and rebuild the kernel. For more information about building kernels, see . The bpf device is already part of the GENERIC kernel that is supplied with FreeBSD, so if you don't have a custom kernel, you shouldn't need to create one in order to get DHCP working. For those who are particularly security conscious, you should be warned that bpf is also the device that allows packet sniffers to work correctly (although they still have to be run as root). bpf is required to use DHCP, but if you are very sensitive about security, you probably shouldn't add bpf to your kernel in the expectation that at some point in the future you will be using DHCP. Edit your /etc/rc.conf to include the following: ifconfig_fxp0="DHCP" Be sure to replace fxp0 with the designation for the interface that you wish to dynamically configure. If you are using a different location for dhclient, or if you wish to pass additional flags to dhclient, also include the following (editing as necessary): dhcp_program="/sbin/dhclient" dhcp_flags="" The DHCP server, dhcpd, is included as part of the isc-dhcp2 port in the ports collection. This port contains the full ISC DHCP distribution, consisting of client, server, relay agent and documentation. Files /etc/dhclient.conf dhclient requires a configuration file, /etc/dhclient.conf. Typically the file contains only comments, the defaults being reasonably sane. This configuration file is described by the &man.dhclient.conf.5; man page. /sbin/dhclient dhclient is statically linked and resides in /sbin. The &man.dhclient.8; manual page gives more information about dhclient. /sbin/dhclient-script dhclient-script is the FreeBSD-specific DHCP client configuration script. It is described in &man.dhclient-script.8;, but should not need any user modification to function properly. /var/db/dhclient.leases The DHCP client keeps a database of valid leases in this file, which is written as a log. &man.dhclient.leases.5; gives a slightly longer description. Further Reading The DHCP protocol is fully described in RFC 2131. An informational resource has also been set up at dhcp.org. + +DNS +Written by Chern Lee clee@serenivision.com, April 12, 2001. + + + + + Overview + FreeBSD utilizes, by default, a version of BIND (Berkeley Internet Name + Domain), which is the most common implementation of the DNS protocol. DNS + is the protocol through which names are mapped to ips, and vice + versa. For example, a query for www.freebsd.org will send back a reply + for the IP address of The FreeBSD Project's webpage, whereas, a query for + ftp.freebsd.org will return the IP of the corresponding ftp + machine. Likewise, the opposite can happen. A query for an ip address + can resolve its hostname. + + + DNS is coordinated across the Internet through a somewhat complex system + of authoritative root name servers, and other smaller-scale nameservers + who host and relay individual domain information. + + + + This document refers to BIND 8.x, as it is the most current, stable + version used in FreeBSD. + + + + RFC1034 and RFC1035 dictates the DNS protocol. + + + + Currently, BIND is maintained by the + Internet Software Consortium (www.isc.org) + + + + + Terminology Used + + zone - Each individual domain, subdomain, + or 'area' dictated by DNS is considered a zone. + + + Examples of zones: + + + + . is the root zone + + + org. is a zone under the root zone + + + foobardomain.org is a zone under the org. zone + + + foo.foobardomain.org. is a subdomain, a zone under the + foobardomain.org. zone + + + + + 1.2.3.in-addr.arpa is a zone referencing all ips which fall under + the 3.2.1.* ip space. + + + + + named, bind, name server - these are all common + names for the BIND name server package within FreeBSD. + + + resolver - a network process by which a system + queries a nameserver for answers + + + root zone - literally, a '.', refers to the root, + or beginning zone. All zones fall under this, as do all files in fall + under the root directory. It is the beginning of the Internet zone + hierarchy + + + origin - refers to the point of start for the + particular zone + + + forward dns - mapping of hostnames to ip addresses + + + reverse dns - the opposite, mapping of ip + addresses to hostnames + + + + + Reasons to run a name server + + + + You need your machine to host DNS information to the world + + + + An authoritative nameserver replies exclusively + to requests. + + + + For example, you register foobardomain.org and wish to assign + hostnames to its proper ip addresses. + + + + A slave nameserver, which replies to queries for a + domain when the primary is down or inaccessible. + + + + The above two can also be done with in-addr.arpa, ip to + hostname entries + + + + + + + You wish your machine to act as a local relay of DNS + information + + + + DNS traffic has been measured to be about 5% or more of + the total Internet traffic. + + + + A local DNS server may have some added benefit by + providing a local cache of DNS information. + + + + + For example, when one queries for www.freebsd.org, their + resolver goes out to (usually) your ISP's name server, and + retreives the query. + + + + + With a local, caching DNS server, the query only has to be + made once to the outside world. Every additional query will + not have to go outside of the local network, since the + information is cached. + + + + + + + + +How it works + + A DNS server in FreeBSD relies on the BIND daemon. This daemon is + called 'named' for obvious reasons. + + + named - the bind daemon + ndc - name daemon control program + + + /etc/namedb - directory where all the bind information + resides + + + /etc/namedb/named.conf - daemon configuration file + + + + zone files are usually contained within the /etc/namedb + directory, and contain the information (query answers from your site) + served by your name server. + + + + + Starting BIND + + Since bind is installed by default, configuring it all is relatively + simple. + + + To ensure the named daemon is started at boot, put the following + modifications in your /etc/rc.conf + + named_enable="YES" + To start the daemon manually (after configuring it) + &prompt.root; ndc start + + + + Configuration files + + make-localhost + Be sure to + + + &prompt.root; cd /etc/namedb + &prompt.root; sh make-localhost + + to properly create your local reverse dns zone file in + /etc/namedb/localhost.rev. + + + + + <filename>/etc/namedb/named.conf</filename> + + +// $FreeBSD: src/etc/namedb/named.conf,v 1.6.2.1 2000/07/15 07:49:29 kris Exp $ +// +// Refer to the named(8) man page for details. If you are ever going +// to setup a primary server, make sure you've understood the hairy +// details of how DNS is working. Even with simple mistakes, you can +// break connectivity for affected parties, or cause huge amount of +// useless Internet traffic. + +options { + directory "/etc/namedb"; + +// In addition to the "forwarders" clause, you can force your name +// server to never initiate queries of its own, but always ask its +// forwarders only, by enabling the following line: +// +// forward only; + +// If you've got a DNS server around at your upstream provider, enter +// its IP address here, and enable the line below. This will make you +// benefit from its cache, thus reduce overall DNS traffic in the +Internet. +/* + forwarders { + 127.0.0.1; + }; +*/ + + + + Just as the comment says, if you want to benefit from your uplink's + cache, you can enable this section of the config file. + + Normally, your nameserver will recursively query different nameservers + until it finds the answer it is looking for. Having this enabled will + have it automatically see if your uplink's (or whatever provided) ns + has the requested query. + + If your uplink has a heavily trafficked, fast nameserver, enabling + this properly could work to your advantage. + + 127.0.0.1 will *NOT* work here; change this to the ip of a nameserver + at your uplink. + + + + /* + * If there is a firewall between you and nameservers you want + * to talk to, you might need to uncomment the query-source + * directive below. Previous versions of BIND always asked + * questions using port 53, but BIND 8.1 uses an unprivileged + * port by default. + */ + // query-source address * port 53; + + /* + * If running in a sandbox, you may have to specify a different + * location for the dumpfile. + */ + // dump-file "s/named_dump.db"; +}; + +// Note: the following will be supported in a future release. +/* +host { any; } { + topology { + 127.0.0.0/8; + }; +}; +*/ + +// Setting up secondaries is way easier and the rough picture for this +// is explained below. +// +// If you enable a local name server, don't forget to enter 127.0.0.1 +// into your /etc/resolv.conf so this server will be queried first. +// Also, make sure to enable it in /etc/rc.conf. + +zone "." { + type hint; + file "named.root"; +}; + +zone "0.0.127.IN-ADDR.ARPA" { + type master; + file "localhost.rev"; +}; + +zone +"0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.INT" { + type master; + file "localhost.rev"; +}; + +// NB: Do not use the IP addresses below, they are faked, and only +// serve demonstration/documentation purposes! +// +// Example secondary config entries. It can be convenient to become +// a secondary at least for the zone where your own domain is in. Ask +// your network administrator for the IP address of the responsible +// primary. +// +// Never forget to include the reverse lookup (IN-ADDR.ARPA) zone! +// (This is the first bytes of the respective IP address, in reverse +// order, with ".IN-ADDR.ARPA" appended.) +// +// Before starting to setup a primary zone, better make sure you fully +// understand how DNS and BIND works, however. There are sometimes +// unobvious pitfalls. Setting up a secondary is comparably simpler. +// +// NB: Don't blindly enable the examples below. :-) Use actual names +// and addresses instead. +// +// NOTE!!! FreeBSD runs bind in a sandbox (see named_flags in rc.conf). +// The directory containing the secondary zones must be write accessible +// to bind. The following sequence is suggested: +// +// mkdir /etc/namedb/s +// chown bind.bind /etc/namedb/s +// chmod 750 /etc/namedb/s + +/* +zone "domain.com" { + type slave; + file "s/domain.com.bak"; + masters { + 192.168.1.1; + }; +}; + +zone "0.168.192.in-addr.arpa" { + type slave; + file "s/0.168.192.in-addr.arpa.bak"; + masters { + 192.168.1.1; + }; +}; +*/ + + + These are example slave entries, read below to see more. + + + For each new domain added to your nameserver, you must add one of + these entries to your named.conf + + + The simplest zone entry, can look like + + +zone "foobardomain.org" { + type master; + file "foorbardomain.org"; +}; + + + For a master entry with the zone information within + foobardomain.org, or + + + +zone "foobardomain.org" { + type slave; + file "foobardomain.org"; +}; + + + + for a slave. Note that slave zones automatically query the listed + master (authoritative) name servers for the zone file. + + + + + Zone files + + An example master 'foobardomain.org' (existing within + /etc/namedb/foobardomain.org) is as follows: + + + +$TTL 3600 + +foobardomain.org. IN SOA ns1.foobardomain.org. admin.foobardomain.org. ( + 5 ; Serial + 10800 ; Refresh + 3600 ; Retry + 604800 ; Expire + 86400 ) ; Minimum TTL + +; DNS Servers +@ IN NS ns1.foobardomain.org. +@ IN NS ns2.foobardomain.org. + +; Machine Names +localhost IN A 127.0.0.1 +ns1 IN A 3.2.1.2 +ns2 IN A 3.2.1.3 +mail IN A 3.2.1.10 +@ IN A 3.2.1.30 + +; Aliases +www IN CNAME @ + +; MX Record +@ IN MX 10 mail.foobardomain.org. + + + + Note that every hostname ending in a '.' is an exact hostname, whereas + everything without a trailing '.' is referenced to the origin. For + example, www is transalated into www + origin. In our ficitious zone + file, our origin is foobardomain.org, so www would be + www.foobardomain.org. + + + + The format of this file follows: + + recordname IN recordtype value + + + The most commonly used DNS records: + + SOA - start of zone authority + NS - an authoritative nameserver + A - A host address + CNAME - the canonical name for an alias + MX - mail exchange + PTR - a domain name pointer (used in reverse + dns) + +foobardomain.org. IN SOA ns1.foobardomain.org. admin.foobardomain.org. ( + 5 ; Serial + 10800 ; Refresh after 3 hours + 3600 ; Retry after 1 hour + 604800 ; Expire after 1 week + 86400 ) ; Minimum TTL of 1 day + + + foobardomain.org. - the domain name, also the + origin for this zone file. + + ns1.foobardomain.org. - the + primary/authoritative nameserver for this zone + + admin.foobardomain.org. - the responsible + person for this zone, e-mail address with @ replaced. + (admin@foobardomain.org becomes admin.foobardomain.org) + + + 5 - the serial number of the file. this must be + incremented each time the zone file is modified. Nowadays, many + admins prefer a yyyymmddrr format for the serial number. 2001041002 + would mean last modified 04/10/2001, the latter 02 being the second + time the zone file has been modified this day. The serial number is + important as it alerts slave nameservers for a zone when it is updated. + + + +@ IN NS ns1.foobardomain.org. + + + This is an NS entry. Every nameserver that is going to reply + authoritatively for the zone must have one of these entries. The @ + is seen here could have been 'foobardomain.org.' The @ transalates to + the origin. + + + +localhost IN A 127.0.0.1 +ns1 IN A 3.2.1.2 +ns2 IN A 3.2.1.3 +mail IN A 3.2.1.10 +@ IN A 3.2.1.30 + + + The A record indicates machine names. As seen above, + ns1.foobardomain.org would resolve to 3.2.1.2. Again, the origin + symbol, @, is used here, thus meaning foobardomain.org would resolve + to 3.2.1.30. + + + +www IN CNAME @ + + + The canonical name record is usually used for giving aliases to a + machine. In the example, www is aliased to the machine addressed to + the origin, or foobardomain.org (3.2.1.30). CNAMEs can be used to + provide alias hostnames, or round robin one hostname among multiple + machines. + + + +@ IN MX 10 mail.foobardomain.org. + + + + The MX record indictes which mail servers are responsible for handling + incoming mail for the zone. mail.foobardomain.org is the hostname of + the mail server, and 10 being the priority of that mailserver. + + + + One can have several mailservers, with priorities of 3, 2, 1. A mail + server attempting to deliver to foobardomain.org would first try the + highest priority MX, then the second highest, etc, until the mail can + be properly delivered. + + + + For in-addr.arpa zone files (reverse dns), the same format is used, + except with PTR entries instead of A or CNAME. + + + +$TTL 3600 + +1.2.3.in-addr.arpa. IN SOA ns1.foobardomain.org. admin.foobardomain.org. ( + 5 ; Serial + 10800 ; Refresh + 3600 ; Retry + 604800 ; Expire + 3600 ) ; Minimum + +@ IN NS ns1.foobardomain.org. +@ IN NS ns2.foobardomain.org. + +2 IN PTR ns1.foobardomain.org. +3 IN PTR ns2.foobardomain.org. +10 IN PTR mail.foobardomain.org. +30 IN PTR foobardomain.org. + + + This file gives the proper ip to hostname mappings of our above + ficticious domain. + + + + + + Caching Name Server + + A caching nameserver is simply a nameserver that is not authoritative for + any zones. It simply asks queries of its own, and remembers them for + later use. To set one up, just configure the name server as usual, omitting any inclusions of zones. + + + + + How to use the nameserver + + If setup properly, the nameserver should be accessible through the + network and locally. /etc/resolv.conf must contain + a nameserver entry with the local ip so it will query the local name + server first. + + + + To access it over the network, the machine must have the nameserver's ip + set properly in its own nameserver configuration options. + + + + + Security + + Although BIND is the most common implementation of DNS, there is + always the issue of security. Possible and exploitable security holes + are sometimes found. + + + + It is a good idea to subscribe to CERT + and + freebsd-announce + to stay up to date with the current Internet and FreeBSD security issues. + + + + If a problem arises, keeping your sources up to date and having a fresh + build of named can't hurt. + + + + + Further Reading + + &man.ndc.8; &man.named.8; &man.named.conf.5; + + + + Official ISC BIND Page + http://www.isc.org/products/BIND/ + + + + BIND FAQ + + http://www.nominum.com/resources/faqs/bind-faqs.html + + + + O'Reilly DNS and BIND 4th Edition + + + + RFC1034 - Domain Names - + Concepts and Facilities + + + + RFC1035 - Domain Names - + Implementation and Specification + + + + + -