Re: strange routing issue--packets stop getting forwarded for a live connection

On 2011-08-21 02:02, Julian Anastasov wrote:

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3. MTU size; 1500 on eth0 and 1406 on tun0. Bigger packets have been
transferred fine.

	Lower MTU, it can be PMTUD problem. At 04:50:24.112658
I see 7801:9169 is 1420 bytes and no ICMP FRAG NEEDED is generated.
May be these two regressions explain it:

http://marc.info/?l=linux-netdev&m=131342172722536&w=2

	There are 2 fixes you can try or more recent kernel
tree, for example 3.1-rc2 has the fixes.

Many thanks for your reply--it looks like you're on to something. You
didn't specify which interface to lower the MTU on, so I tried them each
in turn, and found that lowering the MTU on the client machine to 1406
(matching tun0 on the router) did indeed solve the problem. That makes
sense in retrospect.

	I just wanted to note the difference in MTUs
as a possible cause that triggers the problem. And after
your confirmation I think the new/patched kernel should work
without playing with MTUs.

I finally got a chance to test this, and the patched kernel works fine.
Thank you!

-Corey