From owner-svn-src-head@freebsd.org Mon Sep 7 01:21:57 2015 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 304CC9CB129; Mon, 7 Sep 2015 01:21:57 +0000 (UTC) (envelope-from allanjude@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2001:1900:2254:2068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 1E93EA1F; Mon, 7 Sep 2015 01:21:57 +0000 (UTC) (envelope-from allanjude@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.70]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id t871LuEs054675; Mon, 7 Sep 2015 01:21:56 GMT (envelope-from allanjude@FreeBSD.org) Received: (from allanjude@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id t871Luhr054674; Mon, 7 Sep 2015 01:21:56 GMT (envelope-from allanjude@FreeBSD.org) Message-Id: <201509070121.t871Luhr054674@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: allanjude set sender to allanjude@FreeBSD.org using -f From: Allan Jude Date: Mon, 7 Sep 2015 01:21:56 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r287528 - head/share/man/man4 X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 07 Sep 2015 01:21:57 -0000 Author: allanjude Date: Mon Sep 7 01:21:56 2015 New Revision: 287528 URL: https://svnweb.freebsd.org/changeset/base/287528 Log: Document the sctp blackhole sysctl MIB PR: 184110 Submitted by: Marie Helene Kvello-Aune Reviewed by: wblock Approved by: wblock (mentor) MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D3528 Modified: head/share/man/man4/blackhole.4 Modified: head/share/man/man4/blackhole.4 ============================================================================== --- head/share/man/man4/blackhole.4 Sun Sep 6 22:05:55 2015 (r287527) +++ head/share/man/man4/blackhole.4 Mon Sep 7 01:21:56 2015 (r287528) @@ -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 s 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