netdev - regression kernel 4.4: stops routing packets with a GRE-payload

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Message-ID: <2738275.ziX0sZKPG0@stwm.de>
Date:	Wed, 20 Jan 2016 15:00:52 +0100
From:	Wolfgang Walter <linux@...m.de>
To:	netdev@...r.kernel.org
Subject: regression kernel 4.4: stops routing packets with a GRE-payload

Hello,

we tried 4.4 on our routers. We found one problem: 4.4 stops routing GRE 
packets (ipv4 in GRE/ipv4) here. 4.4.15 works fine.

Neither GRE-endpoint is on the router:

gre-endpoint A <== internet ===> (eth0)router(eth1) <== network ==> gre-
endpoint B

eth0 and eth1 are intel network-cards (I350).

I see GRE-packets arriving both at eth0 and eth1.

GRE-packets from eth0 are not forwarded to eth1 (that means: I can't see them 
with tcpdump on eth1 nor on endpoint B). Packtes with an TCP or UDP payload 
are forwarded.

Some GRE-packets from eth1 are forwarded to eth0 but most just seem to 
disappear.

On the gre-endpoint B (same hardware) which is also a linux router kernel 4.4 
works. So this seems to be a problem when forwarding ipv4-packets with a GRE-
payload.

Regards,
-- 
Wolfgang Walter
Studentenwerk München
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