Multicast overwhelms router

Unanswered Question
Mar 17th, 2008

I have a simple network that consists of 2 2960 switches configured with 2 vlans. There is one uplink to a 2621XM router. IGMP snooping is configured on their switches and IP multicast routing enabled on the router. When some attempts to image workstations all on vlan 2 using multicast (Powercast by Powerquest) the users on vlan 3 can no longer get to sites outside of the router. When I take a trace I see all the multicast packets on the uplink to the router. If I use my packetshaper to rate limit the packets all is right with the world.

1. Is this normal? Should I see all the multicast traffic on the router uplink?

2. If it is not how can I stop this?

I have this problem too.
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Joseph W. Doherty Mon, 03/17/2008 - 17:38

"1. Is this normal? Should I see all the multicast traffic on the router uplink?"

It is for a multicast router. Such a router would normally want to see all multicast traffic so that it could forward it, if needed.

"2. If it is not how can I stop this?"

Suspect you might be dealing with two issues. First, assuming the Powercast is connected at 100 Mbps, and assuming your uplink is only 100 Mbps, your uplink is likely saturated.

Second, a 2621XM really doesn't have the performance to handle sustained 100 Mbps traffic. (Possibly the primary reason other users can't cross the router.)

Try having the host sourcing the multicast run at 10 Mbps. If that's unacceptable, you might try other config options, but suggest better long term solution would be to front 2621XM with a small L3 switch like the 3560-8PC.


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