From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Nicolas_de_Peslo=FCan?= Subject: Re: Problem with ARP-replies on Kernels 2.6 (possibly 3.0, but not 2.4!) Date: Thu, 29 Sep 2011 23:43:02 +0200 Message-ID: <4E84E666.5080003@gmail.com> References: <4E835E35.3030503@gmx.at> <4E837E98.4080608@gmail.com> <4E8390E4.7080104@gmx.at> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE To: skandranon , "netdev@vger.kernel.org" Return-path: Received: from mail-ww0-f44.google.com ([74.125.82.44]:42555 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754921Ab1I2Vmx (ORCPT ); Thu, 29 Sep 2011 17:42:53 -0400 Received: by wwf22 with SMTP id 22so1713649wwf.1 for ; Thu, 29 Sep 2011 14:42:52 -0700 (PDT) In-Reply-To: <4E8390E4.7080104@gmx.at> Sender: netdev-owner@vger.kernel.org List-ID: Le 28/09/2011 23:25, skandranon a =E9crit : >>> So: Is this a bug or a feature? >> >> It is a feature. >> >> You should have a look at the file Documentation/networking/ip-sysct= l in the kernel source tree, >> in particular the entry about arp_ignore. >> >> Nicolas. > Many thanks for your quick reply and the pointer to that document. Please, keep netdev in copy. > Seems this feature has been there a long time already, but this has b= een the first time in all of > the 15 years or so I'm working with Linux that It's bitten my ass. > > May I ask you for an additional pointer explaining in layman's terms = what the use cases for values 2 > and 3 would be? - I plain don't understand. 2 seems obvious and is one more level of strictness. If the ARP seems t= o come from a different=20 subnet, ignore it, even if it enters the host on the "right" interface. I don't know for 3. > And maybe even an explanation what the initial reasoning might have b= een to select the approach of > assigning IP addresses to the host instead of an interface? I think it is expected to enhance connectivity, by being liberal at wha= t the host accept, which is=20 the base principle of interoperability : Be liberal in what you accept,= and conservative in what you=20 send [Jon Postel]. Others may explain this with more history in mind. > The mailing list archive mentioned in e.g. "Understanding Linux Netwo= rk Internals" I found after > having your hint as a starting point doesn't seem to contain this dis= cussion, which has obviously > been old even back in 2003. > And how come that the 2.4.21 kernel did behave differently? The basic= s seem to be the same? Unfortunately, I'm not an archaeologist, so I'm totally unable to answe= r about 2.4.21. Maybe someone=20 else in the list will be. Nicolas.