Multicast problem

Unanswered Question
Aug 18th, 2008

I have a cisco 3845 attached to a foundry switch. Packets to a cluster address that uses mutlicast at layer 2 on the other side of the foundry are not getting through. The 3845 gets an arp entry for the multicast mac address. Other devices on the foundry do not have this problem. Is there something I should configure on the 3845 to ignore the arp responses?

I have this problem too.
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Harold Ritter Mon, 08/18/2008 - 07:57


Here is what RFC1812 section 3.3.2 says about using a link layer multicast address in a ARP reply:

"A router MUST not believe any ARP reply that claims that the Link Layer address of another host or router is a broadcast or multicast address."

The only work around I know is to configure a static arp entry on the router.


rejackson69 Mon, 08/18/2008 - 08:31

Thanks, Sounds like a bug?

I got around it with a static route. I am not sure how it was getting the arp entry but it was not putting an interface in the arp entry.

Harold Ritter Mon, 08/18/2008 - 09:27


It could be a cosmetic bug. Can you please let me know what version of IOS is running on the router as well as post the "sh arp" output.



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