netdev - IPv6 path discovery oddities - flushing the routing cache resolves

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <525E6B03.1040409@blub.net>
Date:	Wed, 16 Oct 2013 12:31:31 +0200
From:	Valentijn Sessink <valentyn@...b.net>
To:	netdev@...r.kernel.org
Subject: IPv6 path discovery oddities - flushing the routing cache resolves

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.

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).

The "server" just has:

auto br0
iface br0 inet6 static
   address 2a01:xxxx:xxx:xxxx::2
   netmask 64
   gateway fe80::1
   bridge_ports eth0
   bridge_maxwait 0

Nothing special, no special routes, no routing daemons.

If I can do anything to shine more light on this issue, please tell me so.

Best regards,

Valentijn
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html