From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Friesen Subject: Re: Linux vs FreeBSD Which is correct. Date: Fri, 19 Aug 2011 10:18:54 -0600 Message-ID: <4E4E8CEE.102@genband.com> References: <4E4BF456.9000807@earthlink.net> <201108172017.48683.remi@remlab.net> <4E4C1A00.80207@earthlink.net> <4E4C2178.1000809@plouf.fr.eu.org> <4E4D08B8.8020309@earthlink.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Pascal Hambourg , =?ISO-8859-1?Q?R=E9mi_Den?= =?ISO-8859-1?Q?is-Courmont?= , Linux Kernel Network Developers To: sclark46@earthlink.net Return-path: Received: from exprod7og104.obsmtp.com ([64.18.2.161]:52613 "EHLO exprod7og104.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756251Ab1HSQTF (ORCPT ); Fri, 19 Aug 2011 12:19:05 -0400 In-Reply-To: <4E4D08B8.8020309@earthlink.net> Sender: netdev-owner@vger.kernel.org List-ID: On 08/18/2011 06:42 AM, Stephen Clark wrote: > I guess I don't really understand what reverse path filter stuff is all > about, much less making it weaker. > But using 2 made the pings responses be seen. It's described in RFC3704. The idea is to block spoofed packets. From Documentation/networking/ip-sysctl.txt: rp_filter - INTEGER 0 - No source validation. 1 - Strict mode as defined in RFC3704 Strict Reverse Path Each incoming packet is tested against the FIB and if the interface is not the best reverse path the packet check will fail. By default failed packets are discarded. 2 - Loose mode as defined in RFC3704 Loose Reverse Path Each incoming packet's source address is also tested against the FIB and if the source address is not reachable via any interface the packet check will fail. Current recommended practice in RFC3704 is to enable strict mode to prevent IP spoofing from DDos attacks. If using asymmetric routing or other complicated routing, then loose mode is recommended. The max value from conf/{all,interface}/rp_filter is used when doing source validation on the {interface}. Default value is 0. Note that some distributions enable it in startup scripts. -- Chris Friesen Software Developer GENBAND chris.friesen@genband.com www.genband.com