[Bridge] R: Re: R: IGMP snooping not filtering multicast messages

maxd at inwind.it maxd at inwind.it
Fri Jun 3 03:50:51 PDT 2011

Hi Herbert,
I gave a look at the RFC4541. Based on what is on page 3, it seems that it 
should be ok to have the bridges generating queries with IP Actually, 
the fact that queries are marked with this IP should allow the receipient to 
understand that the query has not been generated by a router. So, if my 
understanding is correct, the fix could be just to avoid that a bridge assumes 
that a router is present on a link through which a query with address 
is received. What do you think?


>----Messaggio originale----
>Da: herbert at gondor.hengli.com.au
>Data: 03/06/2011 1.29
>A: "maxd at inwind.it"<maxd at inwind.it>
>Cc: <bridge at lists.linux-foundation.org>
>Ogg: Re: R: [Bridge] IGMP snooping not filtering multicast messages
>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, 
>> 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 
>> 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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