Multicast Flooding Network

Unanswered Question


I have a 3560G core switch with a stack of 8 2950's all configured in a ring with spanning-tree turned on to prevent a switching loop.

I'm trying to do Apple ASR multicast imaging to about 50 workstations. I'm using as my multicast address . For some reason all ports are being flooded with the multicast packets. The switches seem to be doing absolutely no multicast filtering/routing even though IGMP snooping is turned on (default settings, basically).

I don't need to route multicast across VLANs or routers or anything like that. I just want to prevent all ports from being flooded with the multicast traffic. Shouldn't this just work by default? It is behaving like broadcast. "show ip igmp snooping groups" on the 3560G doesn't show anything while the imaging is in progress.

Also, I'm am seeing a lot of lost multicast packets for certain clients. I'm streaming at a relatively low rate (6MB/sec) so the bandwidth shouldn't be a problem. I've heard of peopel going as high as 12MB/sec. All machines are at 100Mbit. And there isn't a whole lot else going on in that VLAN. Thoughts?


I have this problem too.
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Jon Marshall Fri, 08/31/2007 - 21:20

Hi Matthew

Have you enabled the IGMP snooping querier on the 3560G switch. Normally a router would act as a querier but a switch can also do this. IGMP snooping is about listening to responses to queries so you have to have something doing the querying.

Attached is a link to config of querier function on a 3560 switch



Anonymous (not verified) Sat, 09/01/2007 - 21:03

nambi_gct Sun, 09/02/2007 - 19:25

Hi Mathew,Do you mean that 3560 floods the traffic.Can you please provide "show ip igmp group" for any vlan and "show ip igmp snooping" for the same vlan?


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