3.4.92 MTU issues

[EgervÃry Gergely]

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?

Thank you in advance,
-- 
Gergely EGERVARY
Network Administrator
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