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Community Member

Multicast packets on trunks

I have two switches connected via ISL trunks. Multicast packets can't get from one switch to the other even though the source and destination are on the same VLAN and is trunked. Shouldn't the switch just pass it on like other layer 2 frames?

4 REPLIES
Blue

Re: Multicast packets on trunks

is igmp enabled?

is ip mls multicast enabled?

what version of switch and routers do you have in the multicast environment?

Community Member

Re: Multicast packets on trunks

The switches are 6509's with sup720's running IOS 12.2. Neither IGMP nor MLS are enabled. I thought that since it's staying on the same VLAN I wouldn't have to do any true multicasting, sort of like EIGRP.

Re: Multicast packets on trunks

The difference is that EIGRP speakers have signaled their intent to listen to multicast traffic. So IGMP Snooping functionality relays that multicast traffic to them.

See

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a008059a9df.shtml

for several solutions to this issue.

Yet another reason to not like NLB....

Michael

Community Member

Re: Multicast packets on trunks

LOL I guess it would affect NLB but that isn't the case here. I forced them to keep the NLB servers on the same switch just in case they couldn't get it to work in unicast mode. This is actually an issue with a ghost application they use to make server images.

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