Subject: Re: IPSec freeze

From: Patrick McHardy <[email-masked]>
Date: Sun, 15 Jul 2007 17:00:40 +0200

Beschorner Daniel wrote:
> Today a new site joined our Linux IPSec VPN, now all the other routers
> (all 2.6.22) freeze hard reproducible.

Do the other routers all do IPsec or just one of them?

> No oops, no sysreq, only hard reset rewakes them.

> 
> The only difference of the new site compared to the others: ADSL, thus a
> MTU of 1492, the others have 1500.
> Disabling IPSec und doing normal operations between the routers is fine,
> PMTU is honored correctly.
> If I set the MTU of the other routers to 1492 I can avoid the IPSec
> crash.
> 
> Some kind of strange need-to-frag-ICMP that causes such things?
> Any ideas how to debug this?

If you can't get any information from your boxes, a testcase that can
be used to reproduce this would help.

> Here a log of another death from inside the tunnel (last packet is again
> the time of crash):
> The Tunnel MTU of 1430 is correct for an outer MTU of 1500, but the
> additional -8 doesn't take place?!?
> 
> 05:17:18.563448 IP 192.168.200.1.80 > 192.168.203.1.3084: tcp 1460
> 05:17:18.563468 IP 192.168.200.254 > 192.168.200.1: ICMP 192.168.203.1
> unreachable - need to frag (mtu 1430), length 556

Does the router use a MTU of 1492 itself or is there another DSL
router or something like that connected by ethernet?