[Bridge] R: IGMP snooping not filtering multicast messages

Herbert Xu herbert at gondor.hengli.com.au
Thu Jun 2 16:29:03 PDT 2011

On Thu, Jun 02, 2011 at 04:27:32PM +0200, maxd at inwind.it wrote:
> I have also tested a scenario with 4 nodes
> A       eb1      B       eb2      ec1      C       ec2       D
> where eb1/eb2 are ports on B, ec1/ec2 are ports on C. eb1/eb2 are bridged 
> together as well as ec1/ec2, so there are now two bridges in the network, on 
> node B and on node C. 
> I have repeated the same test on the 3 nodes scenario, i.e.,
> 1) setup a listener on A
> The IGMP report generated by A is seen on B and C (not on D)
> 2) Send some multicast packets to the group subscribed by A from B 
> Multicast messages are seen on A and C, not on D. 
> Is this correct? I would expect messages just on A, not on C. I have also 
> repeated the test with the multicast_router flag set to 0, but I get the same 
> behaviour.

This is expected because C would have generated queries so B will
mark it as a router and send all multicast packets to it.

Ideally we should end up with just a single querier in a network
so only it needs to see everything.

Right now this doesn't happen because we only send IPv4 queries
with a zero source address.  I'm working on changing this so that
a real IP address can be used.  When that happens whoever has the
lowest IP address numerically out of B/C will be designated as the
querier and the other bridge(s) will then stop sending queries and
will in time stop receiving unsubscribed groups.

I'll let you know when the patch is ready.

Email: Herbert Xu <herbert at gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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