From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Lamparter Subject: Re: Interface without IP address can route?? Date: Wed, 24 Aug 2011 18:15:57 +0200 Message-ID: <20110824161557.GC611458@jupiter.n2.diac24.net> References: <4E5443CD.60502@candelatech.com> <1314190890.25967.114.camel@mojatatu> <4E54FBA6.6090905@candelatech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: jhs@mojatatu.com, jamal , netdev To: Ben Greear Return-path: Received: from spaceboyz.net ([87.106.131.203]:55468 "EHLO spaceboyz.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751689Ab1HXQQH (ORCPT ); Wed, 24 Aug 2011 12:16:07 -0400 Content-Disposition: inline In-Reply-To: <4E54FBA6.6090905@candelatech.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Aug 24, 2011 at 06:24:54AM -0700, Ben Greear wrote: > On 08/24/2011 06:01 AM, jamal wrote: > > It makes sense to behave this way. > > IPv4 addresses are owned by the system not interfaces. > > If you want to control the forwarding behavior, control ARP so it doesnt > > respond on the interfaces with no IP. I agree. > I understand your argument about IPs being owned by system instead of > interface, but I think it's the wrong behaviour in this case. Can > you think of any case where this behaviour actually helps? It's used for oddball /32 setups at server hosting farms that look like: /--- eth0, no ip ---- server 0.1.4.5/32, default via 0.1.2.3 router --- eth1, no ip ---- server 0.1.6.7/32, default via 0.1.2.3 \--- eth2, no ip ---- server 0.1.8.9/32, default via 0.1.2.3 \- eth3: 0.1.2.3/28 - to rest of internet The general idea is to a) conserve IPs and b) not renumber servers even when they move, so you end up with random scattered /32s on the servers and the router has no sensible IP. > Either way, it appears I can work around this by explicitly disabling > forwarding for this particular interface. I was about to suggest exactly this :) David