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

(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
bugzilla-daemon@bugzilla.kernel.org 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: shemminger@linux-foundation.org
        ReportedBy: blueness@gentoo.org
                CC: kernel@gentoo.org
        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.