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New Member

IPv6 multicast routing

Hi, I have a cisco 2811 and running IPv6 MLD. Currently, I configured ethernet and PPP-Sync interfaces for IPv6 multicast. Each interface has a host connected. My problem is when I send multicast traffic from Ethernet to Serial. Everything works, but when sending from Serial to Ethernet, my ethernet host cannot receive traffic. I double check that there is no firewall setup. Can you anyone think of why it only work on one direction, not both?

Thank you

New Member

Re: IPv6 multicast routing

I had a very simular issue during one of my earlier ipv6 depolyment tests.  I would recommend running a packet sniffer and the 1st thing I would look for is to be sure that the ipv6 packets are not exceeding th MTU.

By Default Ipv4, 576 min,  is less than half the size of Ipv6, 1280 min.  Because of this it isn't very hard to exceed the 1500 MTU default, but before you jump to that being the problem I would run the packet sniffer.

Another thing to remember is that ipv6 hop limit for multicast is defaulted to 1.  Thus traffic will not go over routers and depending on your topology it could be the problem.

The final problem that I commonly see is that the multicast reciver application was never started and thus also can replicate your issue.

There are many other problems that it could be, but without packet info it will be just blindly trying things.


oh and be mindful of the MLD versions.

New Member

Re: IPv6 multicast routing


Thanks for the tips. I had a pack sniffer connected. It showed my multicast packets size were 32bytes. Running MLDv2. Since the hop limit is default to 1, how does the message route across two Cisco routers? My networks has at least 2 routers interconnect each other.

Any more suggestion?

Thank you so much for your help.


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