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multicast in same vlan help


i have two 6509 connected to two cat4006 . Each has got trunk to each other. The multicast server in on one cat6509. When the client in same vlan on 4006 joins the group it works, but it stops working then.

Only way to get it owrking is to reboot the PC.. There is not Multicast config aprt from default config on the switches. Can someone help ?

My understanding is the PC sends a Join request when rebooted but wht happens after that ? shou


Re: multicast in same vlan help


Firstly check to insure that you have IGMP enabled, otherwise the Mcast packet will be flooded to all ports within that associated PC vlan.

When it stops issue a sh cam static command on the various switches and make sure you can see the L2 MAC address for the IPmc group.

If this still does not help then you have two option, create a layer3 interface to terminate the Joins or put a static cam entry into the switches with the set cam permanent command.

The other issue is that this could be a bug in the 6500's, if you are runnig 6.3 then it will most likely be a bug which does not programme the LTL correctly for the forwarding ports.

Community Member

Re: multicast in same vlan help

We have the same case in hours Data Centre.

We have two 6509 (CS-A and CS-B) in Port Channel,we have configred LIII of vlan100 here, we have connected two other 6509 (SS-A and SS-3), here we have configurad only lI of vlan100 here.

The multicast server are cabled on SS-A, but the multicast mac-address table don't completed correcly when we put enable the igmp snooping.We have the same situation if we disable the igmp snooping.Finally when the server ,cabled on the CS-B or CS-A and CS-B, make a join in the multicast group the multicast don't running.


Gianluca Magnante

Re: multicast in same vlan help


In connection with my above posting..:) I assume you are both running SUP2 with PFC2's as Cisco has changed the way Mcast is handled from PFC1 to PFC2.

In PFC1 snooping was done on Mcast MAC, in PFC2 it's done only on L3 group address, hence creating a layer3 VLAN and putting PIM on these, this will terminate the IGMP join and thus help building up CAM and shortcuts in the TCAM.

In 7.x CatOS or 12.1E CatIOS you can use IGMP snooping querier command if you do not want to run PIM on the interface.

Also, if all else fails use hte static cam entry, its simple and works


Community Member

Re: multicast in same vlan help


Just to let you know that we managed to resolve the problem by

adding IP multicast-routing and enable ip pim sparse-dense-mode on

VLAN interface.


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