From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: Link-local address handling for IPv4 Date: Tue, 22 Jun 2010 19:21:35 +0200 Message-ID: <1277227295.3057.697.camel@edumazet-laptop> References: <0199E0D51A61344794750DC57738F58E739702DDAE@GVW1118EXC.americas.hpqcorp.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org To: "Fischer, Anna" Return-path: Received: from mail-wy0-f174.google.com ([74.125.82.174]:40299 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756697Ab0FVRVj (ORCPT ); Tue, 22 Jun 2010 13:21:39 -0400 Received: by mail-wy0-f174.google.com with SMTP id 11so50906wyi.19 for ; Tue, 22 Jun 2010 10:21:38 -0700 (PDT) In-Reply-To: <0199E0D51A61344794750DC57738F58E739702DDAE@GVW1118EXC.americas.hpqcorp.net> Sender: netdev-owner@vger.kernel.org List-ID: Le mardi 22 juin 2010 =C3=A0 13:17 +0000, Fischer, Anna a =C3=A9crit : > Hi, >=20 > Does the Linux kernel network stack do any specific handling of=20 > link-local address configuration and handling according to RFC 3927? > I know that there is user-level code like Zeroconf / Avahi and these > tools create ARP sockets directly on the specified network interface= s=20 > in order to support link-local address handling. But if I do not=20 > run any of these tools, does the kernel's ARP code take care of this,= too? >=20 There is no RFC 3927 support in kernel, you need user space support (or switch to DHCP ;) ) Note that ARP replies MUST also be broadcasted for this particular 169.254/16 network (RFC 3927, 2.5), you need a kernel patch too, this was discussed 4 years ago on netdev, and nothing was decided/changed. http://marc.info/?l=3Dlinux-netdev&m=3D114427223811197&w=3D2 BTW I believe that our forwarding path doesnt test source/destination address not being part of 169.254/16 network, I am not sure it is a real problem or not. A netfilter rule can fix it eventually. 7. Router Considerations A router MUST NOT forward a packet with an IPv4 Link-Local source or destination address, irrespective of the router's default route configuration or routes obtained from dynamic routing protocols. A router which receives a packet with an IPv4 Link-Local source or destination address MUST NOT forward the packet. This prevents forwarding of packets back onto the network segment from which they originated, or to any other segment.