Cisco IGMP multicat configuration

Unanswered Question
Jun 8th, 2009


I have the attached the physical network configuration which requires additional configuration to enable Microsoft NLB to work correctly. The servers are attached to the L2 HP switches.

I have followed the guide from cisco and I have created the static arp entries for each of the server pairs that are load balanced.

However my question is when adding the mac-address-table entry what should I include on each switch?

4507R 1 : mac-address-table static xxxx.xxxx.xxxx vlan x interface po3

4507R 2: mac-address-table static xxxx.xxxx.xxxx vlan x interface po3

Do I need to add the trunk between the 2 core switches also (i.e PO1 on both statements above?)

Many Thanks


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Giuseppe Larosa Tue, 06/09/2009 - 04:21

Hello Brian,

I would add the entry also for po1 if you look at the network diagram you can see that it configures it for both interfaces.

if the direct link po3 fails (rare but possible) a multicast packet has to be forwarded to other cisco switch in order to reach other server in cluster.

Hope to help


johnstone_cisco Wed, 06/10/2009 - 02:47

Hi Giuseppe,

Thanks for the feedback!

One further question in relation to this. I also have an number for L2 switches uplinked to the 2 4507 core L3 switches in the diagram, would I need to put any configuration on these switches?



Giuseppe Larosa Wed, 06/10/2009 - 06:28

Hello Brian,

if there are member servers of the MS cluster on them the answer is yes.

With these commands you are manually building the list of ports out whom to replicate traffic for the multicast MAC address.

Hope to help



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