netdev - Re: Question: should local address be expired when updating PMTU?

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Message-ID: <20150203092845.GT13046@secunet.com>
Date:	Tue, 3 Feb 2015 10:28:46 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	shengyong <shengyong1@...wei.com>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>,
	<yangyingling@...wei.com>, <hannes@...hat.com>
Subject: Re: Question: should local address be expired when updating PMTU?

On Mon, Feb 02, 2015 at 04:20:24PM +0800, shengyong wrote:
> Hi, David Miller
> Since commit 81aded246 (ipv6: Handle PMTU in ICMP error handlers), the entries
> in neigh table may get expired. But in the situation:
> 
>           Host only
>     PC <------------> Virtual Machine
> 
> a packet is sent from PC to VM, and the packet looks like:
> -----------------------------------
> | IPv6 (src=PC-addr, dst=VM-addr) |
> |---------------------------------|
> |     ICMPv6 (Packet Too Big)     |
> |---------------------------------|
> | IPv6 (src=VM-addr, dst=VM-addr) |
> |---------------------------------|
> | ICMPv6 (Neighbor Advertisement) |
> -----------------------------------
> 
> Then the local addr on VM will be updated with an expire value. After the
> lifetime of the local addr is expired, the VM is unreachable from PC.
> 
> 	# ip -6 route list table local
> 	local fe80::1 dev lo  metric 0 *expire 596*

We first need to find out why you receive this Packet Too Big message,
can you capture this packet somehow? Then we have to see why this loopback
route gets a pmtu update from that packet. Is the destination address
of the Packet Too Big message really fe80::1?

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