6500 multicasting to 3750

Yang Xia · ‎09-15-2008

2 switches (4506 and 3750) are connected to a core 6509-E via VLAN trunks. Multicast source is on 6509-E. RP config is done. What I see is multicast to 4506 is working fine but not to 3750. IGMP report on 6509-E shows there is a group report from 3750 for that multicast address. However OIL from show ip mr on 6509 still shows Null to subscriber vlan in 3750. What could be the cause that multicast traffic is blocked to 3750?

Thanks in advance for your kind help!

-Yang

Collin Clark · ‎09-15-2008

Yang-

I found a nice trouble shooting doc. Going through it step by step has always fixed my mcast issues.

http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094b55.shtml

Hope that helps.

Yang Xia · ‎09-15-2008

Hi Collin,

Thanks for the pointer. I figured out what is the issue in this case. In vlan SVI on 3750 the pim mode was enabled causing it to be selected as the DR. There is really no need to configure pim mode on the layer2 switch. As soon as I removed it multicasting traffic starts flowing to that vlan.

Regards,

Yang