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Index: head/share/man/man4/blackhole.4
===================================================================
--- head/share/man/man4/blackhole.4
+++ head/share/man/man4/blackhole.4
@@ -12,25 +12,35 @@
.\"
.\"
.\" $FreeBSD$
-.Dd January 1, 2007
+.Dd September 6, 2015
.Dt BLACKHOLE 4
.Os
.Sh NAME
.Nm blackhole
.Nd a
.Xr sysctl 8
-MIB for manipulating behaviour in respect of refused TCP or UDP connection
+MIB for manipulating behaviour in respect of refused SCTP, TCP, or UDP connection
attempts
.Sh SYNOPSIS
-.Cd sysctl net.inet.tcp.blackhole[=[0 | 1 | 2]]
-.Cd sysctl net.inet.udp.blackhole[=[0 | 1]]
+.Cd sysctl net.inet.sctp.blackhole Ns Op = Ns Brq "0 | 1 | 2"
+.Cd sysctl net.inet.tcp.blackhole Ns Op = Ns Brq "0 | 1 | 2"
+.Cd sysctl net.inet.udp.blackhole Ns Op = Ns Brq "0 | 1"
.Sh DESCRIPTION
The
.Nm
.Xr sysctl 8
MIB is used to control system behaviour when connection requests
-are received on TCP or UDP ports where there is no socket listening.
+are received on SCTP, TCP, or UDP ports where there is no socket listening.
.Pp
+The blackhole behaviour is useful to slow down an attacker who is port-scanning
+a system in an attempt to detect vulnerable services.
+It might also slow down an attempted denial of service attack.
+.Ss SCTP
+Setting the SCTP blackhole MIB to a numeric value of one
+will prevent sending an ABORT packet in response to an incoming INIT.
+A MIB value of two will do the same, but will also prevent sending an ABORT packet
+when unexpected packets are received.
+.Ss TCP
Normal behaviour, when a TCP SYN segment is received on a port where
there is no socket accepting connections, is for the system to return
a RST segment, and drop the connection.
@@ -44,20 +54,15 @@
By setting the MIB value to two, any segment arriving
on a closed port is dropped without returning a RST.
This provides some degree of protection against stealth port scans.
-.Pp
-In the UDP instance, enabling blackhole behaviour turns off the sending
+.Ss UDP
+Enabling blackhole behaviour turns off the sending
of an ICMP port unreachable message in response to a UDP datagram which
arrives on a port where there is no socket listening.
It must be noted that this behaviour will prevent remote systems from running
.Xr traceroute 8
to a system.
-.Pp
-The blackhole behaviour is useful to slow down anyone who is port scanning
-a system, attempting to detect vulnerable services on a system.
-It could potentially also slow down someone who is attempting a denial
-of service attack.
.Sh WARNING
-The TCP and UDP blackhole features should not be regarded as a replacement
+The SCTP, TCP, and UDP blackhole features should not be regarded as a replacement
for firewall solutions.
Better security would consist of the
.Nm
@@ -68,6 +73,7 @@
It should be used together with other security mechanisms.
.Sh SEE ALSO
.Xr ip 4 ,
+.Xr sctp 4 ,
.Xr tcp 4 ,
.Xr udp 4 ,
.Xr ipf 8 ,
@@ -80,5 +86,10 @@
MIBs
first appeared in
.Fx 4.0 .
+.Pp
+The SCTP
+.Nm
+MIB first appeared in
+.Fx 9.1 .
.Sh AUTHORS
.An Geoffrey M. Rehmet

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