From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Frederic Sowa Subject: Re: IPv6 path discovery oddities - flushing the routing cache resolves Date: Wed, 16 Oct 2013 17:48:41 +0200 Message-ID: <20131016154841.GC18135@order.stressinduktion.org> References: <525E6B03.1040409@blub.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: netdev@vger.kernel.org To: Valentijn Sessink Return-path: Received: from order.stressinduktion.org ([87.106.68.36]:38773 "EHLO order.stressinduktion.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755206Ab3JPPsm (ORCPT ); Wed, 16 Oct 2013 11:48:42 -0400 Content-Disposition: inline In-Reply-To: <525E6B03.1040409@blub.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Oct 16, 2013 at 12:31:31PM +0200, Valentijn Sessink wrote: > Hello list, > > I'm experiencing difficulties with IPv6 path discovery. The setup is > quite simple, a machine with native IPv6, no special routing - let's > call it the "server" for now. Unfortunately, I seem to loose > connectivity multiple times a day - and after digging in, I found this > to be "too big" messages that weren't honored at the server. The network > consists of something like: > > server --- hosting --- others ---- SIXXS tunnel with 1280 MTU --- me. > > A "ip -6 route list cache" would show a cached route to my "client", but > one without MTU. Then after "ip -6 route flush cache", and after trying > to send a large packet (for example issuing "ps uaxww" on an ssh > prompt), "ip -6 route list cache" will show a correct MTU. Oh, thats another very good hint. > But after a while, things start to go wrong again, and another "ip -6 > route flush cache" is needed. > > The server is running 3.8.0-something (ubuntu 12.04 with a newer kernel). > > tcpdump shows that on reception of icmpv6 "too big", nothing happens > (i.e. the "too big" packet will be sent time and again), and after the > "ip -6 route flush cache", suddenly the "too big" message is honored. > > I saw a couple of path discovery issues on this list, more specifically > one with the subject "IPv6 path MTU discovery broken" earlier this month > - but I'm not sure it's the same issue (because the original submitter > specifically mentions kernels 3.10 and 3.11 and has a much more > complicated routing table). I do think these two issues are connected. Could you send me a the corresponding ip route output and /proc/net/ipv6_route output for when it works and mtus are correctly handled and when it does not work? Thanks, Hannes