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Advanced NetworkingSynopsisThe 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 RoutesContributed 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 exampleTo 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 0The 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:UUp: The route is active.HHost: The route destination is a single host.GGateway: Send anything for this destination on to this
remote system, which will figure out from there where to send
it.SStatic: This route was configured manually, not
automatically generated by the system.CClone: Generates a new route based upon this route for
machines we connect to. This type of route is normally used
for local networks.WWasCloned: Indicated a route that was auto-configured
based upon a local area network (Clone) route.LLink: Route involves references to ethernet
hardware.Default routesWhen 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:hostdefault gatewayinterfaceLocal2Local1ethernetLocal1T1-GWPPPA 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 hostsThere 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 propagationWe 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.TroubleshootingSometimes, 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;.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.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 NFSLuckily 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 modificationss to your /etc/rc.conf
file.On the NFS server make sure you have:
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 curlyThe 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 10.0.0.4The 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.comIn 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; nfsd -u -t -n 4
&prompt.root; mountd -rOn the NFS client:&prompt.root; nfsiod -n 4Now 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 /mntThis 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 2 2Read the &man.fstab.5; man page for more options.Practical UsesThere 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 systemsContributed 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 0As a manual mount command on freebox:&prompt.root; mount -t nfs -o -r=1024 fastws:/sharedfs /projectExamples for the FreeBSD system as the server: in
/etc/fstab on fastws:
freebox:/sharedfs /project nfs rw,-w=1024 0 0As a manual mount command on fastws:&prompt.root; mount -t nfs -o -w=1024 freebox:/sharedfs /projectNearly 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 OperationContributed 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 InstructionsFind 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:helpprint help listip
print/set client's IP addressserver
print/set bootp/tftp server addressnetmask
print/set netmaskhostname nameprint/set hostnamekernel
print/set kernel namerootfs
print/set root filesystemswapfs
print/set swap filesystemswapsize
set diskless swapsize in Kbytesdiskbootboot from diskautobootcontinue boot processtrans
|turn transceiver on|offflags
set boot flagsA typical completely diskless cfg file might contain:
rootfs 192.1.2.3:/rootfs/myclient
swapfs 192.1.2.3:/swapfs
swapsize 20000
hostname myclient.mydomainA cfg file for a machine with local swap might contain:
rootfs 192.1.2.3:/rootfs/myclient
hostname myclient.mydomainEnsure 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.mydomainAnd on HP-UX:
/rootfs/myclient -root=myclient.mydomain
/swapfs -root=myclient.mydomainIf 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,
eg:&prompt.root; dd if=/dev/zero of=/swapfs/swap.192.1.2.4 bs=1k count=20000Also, 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.192.1.2.4Unpack 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 fileUsing Shared / and /usr
filesystemsAt 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 setupsNetboot 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.ISDNLast modified by &a.wlloyd;.A good resource for information on ISDN technology and hardware is
Dan Kegel's ISDN
Page.A quick simple roadmap 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 dialup 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 CardsContributed 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-isdnin the body of your message.ISDN Terminal AdaptersTerminal 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 standalone 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 ProAdtranMost 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 standalone
router, and with a simple 386 FreeBSD box driving it, probably more
flexible.The choice of sync/TA vs standalone 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.Standalone ISDN Bridges/RoutersISDN 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 networkNetwork 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)
|
Standalone router
|
ISDN BRI lineIf your home/branch office is only one computer you can use a
twisted pair crossover cable to connect to the standalone router
directly.Head office or other lanNetwork is Twisted Pair Ethernet.
-------Novell Server
| H |
| ---Sun
| |
| U ---FreeBSD
| |
| ---Windows 95
| B |
|___---Standalone router
|
ISDN BRI lineOne 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 internet 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
dialin, dialout 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/YPWritten by &a.unfurl;, 21 January 2000.What is it? NIS is an 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.How does it work?There are 3 types of hosts in an NIS enviornment; master
servers, slave servers, and clients. Servers act as a central
repository for host configuration information. Master servers
hold the authoritatve 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.Using NIS/YPPlanningIf 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 NameThis 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.Physical Server RequirementsThere are several things to keep in mind when chosing 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 serverSetting up a master NIS server can be relativly straight
forward, depending on your needs. FreeBSD comes with a handy
script called ypinit that makes the initial
setup procedure very easy. A few steps are needed ahead of
time to make the setup process go smoothly.Make sure your NIS domainname is set, using the
domainname command. You can run
ypinit for domains other than the one
your host is in but if domainname is
not set, now is a good time to do so.Make sure a copy of the
master.passwd file is in
/var/yp. This where NIS will get the
password entries it will share with it's clients.
ypinit runs with errors if this file is
not present. You can either start a new
master.passwd or copy the existing
one from /etc/master.passwd. If you
do the latter, make sure the permissions are set properly
to disallow world/group reading of the file.Start the ypserv daemon.
ypinit requires
ypserv to be running to answer some RPC
calls it makes. In its basic configuration
ypserv does not need to be run with any
flags.Once you've done the above steps, run
ypinit with the flag.
You might want to specify the domain you are building a master
server for if it is different than what the
domainname is set to. In this example,
test-domain will be our NIS
domainname.
# 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.
master.example.com 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 : master.example.com
next host to add: ^D
The current list of NIS servers looks like this:
master.example.com
Is this correct? [y/n: y] y
Building /var/yp/test-domain/ypservers...
Running /var/yp/Makefile...
NIS Map update started on Fri Dec 3 16:54:12 PST 1999 for domain test-domain
Updating hosts.byname...
Creating new /var/yp/passwd file from /var/yp/master.passwd...
Updating netid.byname...
Updating hosts.byaddr...
Updating networks.byaddr...
Updating networks.byname...
Updating protocols.bynumber...
Updating protocols.byname...
Updating rpc.byname...
Updating rpc.bynumber...
Updating services.byname...
Updating group.byname...
Updating group.bygid...
Updating passwd.byname...
Updating passwd.byuid...
Updating master.passwd.byname...
Updating master.passwd.byuid...
NIS Map update completed.
master.example.com has been setup as an YP master server without any errors.There are a few crucial lines that need to be added to
your /etc/rc.conf in order for the NIS
server to start properly. Make sure that these lines are
included:
nis_server_enable="YES"
nis_server_flags=""
nis_yppasswdd_enable="YES"
nis_yppasswdd_flags=""You will most likely want to run
yppasswd on the NIS server. This allows
users on NIS client machines to change their passwords and
other user information remotely. Setting up a NIS slave serverSetting up an NIS slave server is even more simple than
setting up the master. Again the ypinit
command helps out a great deal. As in the previous example
we'll use “test-domain” as our target NIS
domainname.
# ypinit -s master.example.com test-domain
Server Type: SLAVE Domain: test-domain Master: master.example.com
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 master.example.com.
Transfering netgroup...
ypxfr: Exiting: Map successfully transfered
Transfering netgroup.byuser...
ypxfr: Exiting: Map successfully transfered
Transfering netgroup.byhost...
ypxfr: Exiting: Map successfully transfered
Transfering master.passwd.byuid...
ypxfr: Exiting: Map successfully transfered
Transfering passwd.byuid...
ypxfr: Exiting: Map successfully transfered
Transfering passwd.byname...
ypxfr: Exiting: Map successfully transfered
Transfering group.bygid...
ypxfr: Exiting: Map successfully transfered
Transfering group.byname...
ypxfr: Exiting: Map successfully transfered
Transfering services.byname...
ypxfr: Exiting: Map successfully transfered
Transfering rpc.bynumber...
ypxfr: Exiting: Map successfully transfered
Transfering rpc.byname...
ypxfr: Exiting: Map successfully transfered
Transfering protocols.byname...
ypxfr: Exiting: Map successfully transfered
Transfering master.passwd.byname...
ypxfr: Exiting: Map successfully transfered
Transfering networks.byname...
ypxfr: Exiting: Map successfully transfered
Transfering networks.byaddr...
ypxfr: Exiting: Map successfully transfered
Transfering netid.byname...
ypxfr: Exiting: Map successfully transfered
Transfering hosts.byaddr...
ypxfr: Exiting: Map successfully transfered
Transfering protocols.bynumber...
ypxfr: Exiting: Map successfully transfered
Transfering ypservers...
ypxfr: Exiting: Map successfully transfered
Transfering hosts.byname...
ypxfr: Exiting: Map successfully transfered
slave.example.com has been setup as an YP slave server without any errors.
Don't forget to update map ypservers on master.example.com.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.byuidThese 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.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 clientSetting up a FreeBSD machine to be a NIS client is fairly
straight forward.Set the host's NIS domainname with the
domainname command, or at boot time
with this entry in
/etc/rc.conf:nisdomainname="test-domain"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. 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 SecurityIn 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
10.0.0.0 255.255.240.0If 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 both
vulnerable to “IP spoofing” attacks.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 vs. libdescryptOne 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.aIf the machine is configured to use the standard FreeBSD MD5
crypt libraries they will look somethine 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.aIf you have trouble authenticating on an NIS client, this is a
pretty good place to start looking for possible problems.DHCPWritten 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 coversThis 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 WorksWhen 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 IntegrationFreeBSD 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.To have your system use DHCP to obtain network information
upon startup, 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.confdhclient 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/dhclientdhclient is statically linked and
resides in /sbin. The &man.dhclient.8;
manual page gives more information about
dhclient./sbin/dhclient-scriptdhclient-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.leasesThe 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 ReadingThe DHCP protocol is fully described in
RFC 2131.
An informational resource has also been set up at
dhcp.org.
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 16f2fe153a..d8851c39eb 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
@@ -1,1811 +1,1813 @@
Advanced NetworkingSynopsisThe 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 RoutesContributed 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 exampleTo 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 0The 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:UUp: The route is active.HHost: The route destination is a single host.GGateway: Send anything for this destination on to this
remote system, which will figure out from there where to send
it.SStatic: This route was configured manually, not
automatically generated by the system.CClone: Generates a new route based upon this route for
machines we connect to. This type of route is normally used
for local networks.WWasCloned: Indicated a route that was auto-configured
based upon a local area network (Clone) route.LLink: Route involves references to ethernet
hardware.Default routesWhen 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:hostdefault gatewayinterfaceLocal2Local1ethernetLocal1T1-GWPPPA 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 hostsThere 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 propagationWe 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.TroubleshootingSometimes, 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;.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.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 NFSLuckily 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 modificationss to your /etc/rc.conf
file.On the NFS server make sure you have:
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 curlyThe 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 10.0.0.4The 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.comIn 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; nfsd -u -t -n 4
&prompt.root; mountd -rOn the NFS client:&prompt.root; nfsiod -n 4Now 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 /mntThis 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 2 2Read the &man.fstab.5; man page for more options.Practical UsesThere 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 systemsContributed 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 0As a manual mount command on freebox:&prompt.root; mount -t nfs -o -r=1024 fastws:/sharedfs /projectExamples for the FreeBSD system as the server: in
/etc/fstab on fastws:
freebox:/sharedfs /project nfs rw,-w=1024 0 0As a manual mount command on fastws:&prompt.root; mount -t nfs -o -w=1024 freebox:/sharedfs /projectNearly 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 OperationContributed 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 InstructionsFind 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:helpprint help listip
print/set client's IP addressserver
print/set bootp/tftp server addressnetmask
print/set netmaskhostname nameprint/set hostnamekernel
print/set kernel namerootfs
print/set root filesystemswapfs
print/set swap filesystemswapsize
set diskless swapsize in Kbytesdiskbootboot from diskautobootcontinue boot processtrans
|turn transceiver on|offflags
set boot flagsA typical completely diskless cfg file might contain:
rootfs 192.1.2.3:/rootfs/myclient
swapfs 192.1.2.3:/swapfs
swapsize 20000
hostname myclient.mydomainA cfg file for a machine with local swap might contain:
rootfs 192.1.2.3:/rootfs/myclient
hostname myclient.mydomainEnsure 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.mydomainAnd on HP-UX:
/rootfs/myclient -root=myclient.mydomain
/swapfs -root=myclient.mydomainIf 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,
eg:&prompt.root; dd if=/dev/zero of=/swapfs/swap.192.1.2.4 bs=1k count=20000Also, 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.192.1.2.4Unpack 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 fileUsing Shared / and /usr
filesystemsAt 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 setupsNetboot 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.ISDNLast modified by &a.wlloyd;.A good resource for information on ISDN technology and hardware is
Dan Kegel's ISDN
Page.A quick simple roadmap 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 dialup 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 CardsContributed 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-isdnin the body of your message.ISDN Terminal AdaptersTerminal 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 standalone 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 ProAdtranMost 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 standalone
router, and with a simple 386 FreeBSD box driving it, probably more
flexible.The choice of sync/TA vs standalone 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.Standalone ISDN Bridges/RoutersISDN 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 networkNetwork 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)
|
Standalone router
|
ISDN BRI lineIf your home/branch office is only one computer you can use a
twisted pair crossover cable to connect to the standalone router
directly.Head office or other lanNetwork is Twisted Pair Ethernet.
-------Novell Server
| H |
| ---Sun
| |
| U ---FreeBSD
| |
| ---Windows 95
| B |
|___---Standalone router
|
ISDN BRI lineOne 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 internet 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
dialin, dialout 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/YPWritten by &a.unfurl;, 21 January 2000.What is it? NIS is an 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.How does it work?There are 3 types of hosts in an NIS enviornment; master
servers, slave servers, and clients. Servers act as a central
repository for host configuration information. Master servers
hold the authoritatve 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.Using NIS/YPPlanningIf 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 NameThis 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.Physical Server RequirementsThere are several things to keep in mind when chosing 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 serverSetting up a master NIS server can be relativly straight
forward, depending on your needs. FreeBSD comes with a handy
script called ypinit that makes the initial
setup procedure very easy. A few steps are needed ahead of
time to make the setup process go smoothly.Make sure your NIS domainname is set, using the
domainname command. You can run
ypinit for domains other than the one
your host is in but if domainname is
not set, now is a good time to do so.Make sure a copy of the
master.passwd file is in
/var/yp. This where NIS will get the
password entries it will share with it's clients.
ypinit runs with errors if this file is
not present. You can either start a new
master.passwd or copy the existing
one from /etc/master.passwd. If you
do the latter, make sure the permissions are set properly
to disallow world/group reading of the file.Start the ypserv daemon.
ypinit requires
ypserv to be running to answer some RPC
calls it makes. In its basic configuration
ypserv does not need to be run with any
flags.Once you've done the above steps, run
ypinit with the flag.
You might want to specify the domain you are building a master
server for if it is different than what the
domainname is set to. In this example,
test-domain will be our NIS
domainname.
# 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.
master.example.com 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 : master.example.com
next host to add: ^D
The current list of NIS servers looks like this:
master.example.com
Is this correct? [y/n: y] y
Building /var/yp/test-domain/ypservers...
Running /var/yp/Makefile...
NIS Map update started on Fri Dec 3 16:54:12 PST 1999 for domain test-domain
Updating hosts.byname...
Creating new /var/yp/passwd file from /var/yp/master.passwd...
Updating netid.byname...
Updating hosts.byaddr...
Updating networks.byaddr...
Updating networks.byname...
Updating protocols.bynumber...
Updating protocols.byname...
Updating rpc.byname...
Updating rpc.bynumber...
Updating services.byname...
Updating group.byname...
Updating group.bygid...
Updating passwd.byname...
Updating passwd.byuid...
Updating master.passwd.byname...
Updating master.passwd.byuid...
NIS Map update completed.
master.example.com has been setup as an YP master server without any errors.There are a few crucial lines that need to be added to
your /etc/rc.conf in order for the NIS
server to start properly. Make sure that these lines are
included:
nis_server_enable="YES"
nis_server_flags=""
nis_yppasswdd_enable="YES"
nis_yppasswdd_flags=""You will most likely want to run
yppasswd on the NIS server. This allows
users on NIS client machines to change their passwords and
other user information remotely. Setting up a NIS slave serverSetting up an NIS slave server is even more simple than
setting up the master. Again the ypinit
command helps out a great deal. As in the previous example
we'll use “test-domain” as our target NIS
domainname.
# ypinit -s master.example.com test-domain
Server Type: SLAVE Domain: test-domain Master: master.example.com
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 master.example.com.
Transfering netgroup...
ypxfr: Exiting: Map successfully transfered
Transfering netgroup.byuser...
ypxfr: Exiting: Map successfully transfered
Transfering netgroup.byhost...
ypxfr: Exiting: Map successfully transfered
Transfering master.passwd.byuid...
ypxfr: Exiting: Map successfully transfered
Transfering passwd.byuid...
ypxfr: Exiting: Map successfully transfered
Transfering passwd.byname...
ypxfr: Exiting: Map successfully transfered
Transfering group.bygid...
ypxfr: Exiting: Map successfully transfered
Transfering group.byname...
ypxfr: Exiting: Map successfully transfered
Transfering services.byname...
ypxfr: Exiting: Map successfully transfered
Transfering rpc.bynumber...
ypxfr: Exiting: Map successfully transfered
Transfering rpc.byname...
ypxfr: Exiting: Map successfully transfered
Transfering protocols.byname...
ypxfr: Exiting: Map successfully transfered
Transfering master.passwd.byname...
ypxfr: Exiting: Map successfully transfered
Transfering networks.byname...
ypxfr: Exiting: Map successfully transfered
Transfering networks.byaddr...
ypxfr: Exiting: Map successfully transfered
Transfering netid.byname...
ypxfr: Exiting: Map successfully transfered
Transfering hosts.byaddr...
ypxfr: Exiting: Map successfully transfered
Transfering protocols.bynumber...
ypxfr: Exiting: Map successfully transfered
Transfering ypservers...
ypxfr: Exiting: Map successfully transfered
Transfering hosts.byname...
ypxfr: Exiting: Map successfully transfered
slave.example.com has been setup as an YP slave server without any errors.
Don't forget to update map ypservers on master.example.com.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.byuidThese 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.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 clientSetting up a FreeBSD machine to be a NIS client is fairly
straight forward.Set the host's NIS domainname with the
domainname command, or at boot time
with this entry in
/etc/rc.conf:nisdomainname="test-domain"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. 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 SecurityIn 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
10.0.0.0 255.255.240.0If 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 both
vulnerable to “IP spoofing” attacks.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 vs. libdescryptOne 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.aIf the machine is configured to use the standard FreeBSD MD5
crypt libraries they will look somethine 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.aIf you have trouble authenticating on an NIS client, this is a
pretty good place to start looking for possible problems.DHCPWritten 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 coversThis 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 WorksWhen 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 IntegrationFreeBSD 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.To have your system use DHCP to obtain network information
upon startup, 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.confdhclient 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/dhclientdhclient is statically linked and
resides in /sbin. The &man.dhclient.8;
manual page gives more information about
dhclient./sbin/dhclient-scriptdhclient-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.leasesThe 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 ReadingThe DHCP protocol is fully described in
RFC 2131.
An informational resource has also been set up at
dhcp.org.