All things related to multicast

[Alan Crosswell <>]

Jeff Fitzwater wrote:
> This may be slightly off topic but you guys must know the answer to this.
>
>
> I believe I understand how IGMP SNOOPING works and everything I have 
> read and tested tells me that the MULTICAST DATA will always be passed 
> toward the QUERIER (This should be the router in most cases).    Is this 
> correct and works as designed so it can handle non-IGMP capable routers 
> that do not generate JOINS (REPORTS).
>
> In our case we have the multicast SRC and CLIENT downstream of the 
> router but the router is the QUERIER, so therefor the downstream switch 
> hears the report from the client and adds it to his table.  Now when the 
> multicast data flows it not only goes out to the client but also out 
> toward the QUERIER (router).
>
> I would think this would just suck up unnecessary BW on the router link.
>
>
> Q.   Does the data always get sent to the QUERIER even if there are no 
> listeners at the router ???

Yes, this is my understanding.  The switch has no way of knowing whether there 
are listeners upstream of the router so the data has to go there always.
/a

> I hope I described it OK.
>
>
> Thanks for any response.
>
>
>
> Jeff Fitzwater
> OIT Network Systems
> Princeton University