netdev - Re: 3.4.92 MTU issues

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Message-ID: <CAADnVQ+q3wFf=j0TY57d6Ux4GyGLr0bVCFHDgA45n9rXiEEzjg@mail.gmail.com>
Date:	Tue, 10 Jun 2014 14:16:54 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Egerváry Gergely <gergely@...rvary.hu>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Florian Westphal <fw@...len.de>
Subject: Re: 3.4.92 MTU issues

cc-ing netdev

On Tue, Jun 10, 2014 at 12:43 PM, Egerváry Gergely <gergely@...rvary.hu> wrote:
> Hi,
>
> we have just upgraded our systems from 3.4.91 (longterm) to 3.4.92.
> Since then we are experiencing dozens of MTU-related network timeout
> issues. Reverting back to 3.4.91 fixes all of these problems.
>
> Both kernel versions are built from vanilla sources with the same
> .config. These can be highly reproduced over VPN tunnels or even over
> simple ethernet connections when using DNAT. (TCP port forward) It
> looks like MTU path discovery is somehow affected.
>
> ICMP is not filtered in our network. (For testing, we flushed all
> iptables rules, set all policies to ACCEPT, and problem still exists.)
> We do not use any special sysctl settings. Was there any changes
> related to packet forwarding or MTU discovery?

some combination of old kernel and backport of ("net: ipv4:
ip_forward: fix inverted local_df test") ?
just guessing

> Thank you in advance,
> --
> Gergely EGERVARY
> Network Administrator
> --
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