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

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 05 octobre 2011 à 13:09 -0700, Ben Greear a écrit :
> On 10/05/2011 12:54 PM, Eric Dumazet wrote:
> > 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.
> 
> I see packets get to this code in ip_input.c (line 467 or so),
> and that printk is mine of course.
> 
> 	if ((dev && strcmp(dev->name, "rddVR10#0") == 0) ||
> 	    (dev && strcmp(dev->name, "rddVR10") == 0)) {
> 		printk("calling ip_rcv_finish through NF_HOOK, dev: %s, len: %i\n",
> 		       dev->name, skb->len);
> 	}
> 
> 	return NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING, skb, dev, NULL,
> 		       ip_rcv_finish);
> 
> But, the macvlan packets never make it to the ip_rcv_finish method.
> 
> I do see a big and a little packet entering this code.
> 
> I have no firewall rules that I'm aware of, though there
> is some conn-track logic (though not associated with the
> mac-vlan interface):

Say you have 10 vlans on your eth0, how many times do you want one
incoming multicast frame being delivered to your application listening
on 0.0.0.0:port ?

10 or 1 ?