diff options
author | allanjude <allanjude@FreeBSD.org> | 2016-01-12 05:53:53 +0000 |
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committer | allanjude <allanjude@FreeBSD.org> | 2016-01-12 05:53:53 +0000 |
commit | 3ab020832b3c8030648d1c333d7bfaa36bacd480 (patch) | |
tree | 29ac131368da64e7429057d6c76898d8e10af423 /share | |
parent | e5730b26f0bf718ff736aa36cc01c92c46fe7518 (diff) | |
download | FreeBSD-src-3ab020832b3c8030648d1c333d7bfaa36bacd480.zip FreeBSD-src-3ab020832b3c8030648d1c333d7bfaa36bacd480.tar.gz |
MFC: r287528
Document the sctp blackhole sysctl MIB
PR: 184110
Submitted by: Marie Helene Kvello-Aune <marieheleneka@gmail.com>
Diffstat (limited to 'share')
-rw-r--r-- | share/man/man4/blackhole.4 | 37 |
1 files changed, 24 insertions, 13 deletions
diff --git a/share/man/man4/blackhole.4 b/share/man/man4/blackhole.4 index 668f92d..f662ec3 100644 --- a/share/man/man4/blackhole.4 +++ b/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 @@ as a blackhole. 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 @@ This mechanism is not a substitute for securing a system. 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 @@ The TCP and UDP MIBs first appeared in .Fx 4.0 . +.Pp +The SCTP +.Nm +MIB first appeared in +.Fx 9.1 . .Sh AUTHORS .An Geoffrey M. Rehmet |