Subject: Re: [Bugme-new] [Bug 36122] New: New cache learned PMTU information in inetpeer causes ssh to fail when tunneled via an IPSEC VPN

From: Andrew Morton <[email-masked]>
Date: Mon, 6 Jun 2011 13:48:41 -0700

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Sat, 28 May 2011 21:50:32 GMT
[email-masked] wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=36122
> 
>                URL: http://bugs.gentoo.org/show_bug.cgi?id=369025
>            Summary: New cache learned PMTU information in inetpeer causes
>                     ssh to fail when tunneled via an IPSEC VPN
>            Product: Networking
>            Version: 2.5
>     Kernel Version: 2.6.39
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: IPV4
>         AssignedTo: [email-masked]
>         ReportedBy: [email-masked]
>                 CC: [email-masked]
>         Regression: No
> 
> 
> When trying to ssh from a box running 2.6.39 on one private subnet to another
> box on another private subnet via an IPSEC vpn, ssh freezes and times out at:
> 
>    debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
> 
> This was traced down to commit 2c8cec5c10bced2408082a6656170e74ac17231c.
> 
> This type of error is known to occur when there is fragmentation due to
> mismatched mtu's which the commit addresses.
> 
> Notice the problem does not occur when ssh-ing directly, ie not via an IPSEC
> tunnel.  I have not tested if other tunnels are affected.
> 
> Please see the downstream bug for more details.
>