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Multicast traffic in catalyst 6509 also hits the loadbalancer port-channel 259

The catalyst 6509 in our mediafarm is running an old release: s72033-pk9s-mz.122-18.SXD3.bin.

This catalysts has a firewall module and a loadbalancer module in it.

We run about 400Mbps multicast traffic in vlan550 for our TV service, this traffic should not go via the load-balancer,

BUT we do see it going over the port-channel towards both.

How can we avoid this?

See the attached file, the vlan is shown, the inventory, the running-config , and the load on the port-channel

Cisco Employee

Re: Multicast traffic in catalyst 6509 also hits the loadbalance

Hi there,

if I am understanding right the mcast traffic in vlan550 should stay at L2 (that is, it is not supposed to be routed out of that vlan) as I don't see any type of pim configured on that interface (or on others).

That means that in order to avoid the flooding of such L2 multicast on all interfaces in vlan550 (I suppose that your load-balancer and firewall modules have 'legs' in vlan550 too) we need IGMP snooping to kick in. As the name implies this feature uses IGMP reports (IGMP joins) sent to reply to IGMP membership queries. Without such joins IGMP snooping cannot build the L2 mac address table with the information about which specific L2 ports need to receive mcast streams.

The point is that if no host/router sends a membership query no host will reply with a join and the traffic will be flooded at l2 forever.

If my understanding is right you need to configure a 'querier' in vlan550 for the interested receivers to send a join and avoid the flooding. It can be any router with ip pim configured (pim sparse mode for instance) including interface vlan550 itself of your 6500. or you can configure igmp snooping querier feature under vlan 550, which is just a feature which send membership reports in a given vlan, but I am not sure whether your veeeeeeeeeeeeeeery old IOS already supports it.

As background info have a look at this 2 documents on igmp snooping (and also on the querier)

Let me know if this helps


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