netdev - Re: IPv4 multicast and mac-vlans acting weird on 3.0.4+

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Date:	Wed, 05 Oct 2011 21:54:09 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: IPv4 multicast and mac-vlans acting weird on 3.0.4+

Le mercredi 05 octobre 2011 à 09:46 -0700, Ben Greear a écrit :
> This is on a hacked 3.0.4 kernel...
> 
> I am seeing an issue where an IPv4 mcast receiver will not receive
> a 1473 or larger byte mcast message, but will receive a 1472.  The difference
> being that 1473 ends up being two packets on the wire.  It works on
> 802.1Q VLANs, VETH interfaces and real Ethernet.  It does not work
> on a mac-vlan hanging off the VETH.
> 
> I see packets received on the macvlan in tshark, and they appear correct.  No
> obvious errors in the macvlan port stats or netstat -s,
> and the 'ss' tool doesn't appear to support UDP sockets at all.
> 
> So, I'm about to go digging into the code, but if anyone has any
> suggestions for places to look, please let me know!
> 

Well, problem is defragmentation and macvlan cooperation.

Multicast messages are broadcasted on all macvlan ports.

But IP defrag will probably deliver a single final frame.

We probably need to handle defrag in macvlan before broadcasting to all
ports.



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