Microsoft NLB , Catalyst 6000

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Sep 29th, 2009
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Hi all,

I want to configure Microsoft NLB on the Catalyst 6000 running IOS version 12.2SX,

It is necessary to activate ip multicast-routing ? If I activate multicast routing which impact have my Network ?

Thank you


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xcz504d1114 Tue, 09/29/2009 - 13:04
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No it is not necessary to activate multicast routing. You will need to make static ARP entries on your routers for the servers though.

The multicast setting in the NLB cluster setup refers to the mac-address not the IP address. Multicast routing is based on the IP address not the mac-address.

Windows 2008 using NLB and multicast mac's had some undesireable effects on my network, I don't know if it was a combination hardware / OS or not. We have ours in IBM blade chassis, and once in a while my core would psike to 100% CPU utilization, turns out the NLB cluster was sending out 70k ARP's per second, so if it is an option, I would advise you to configure storm control on your core.

We ended up moving away from the multicast setting and used unicast.



platinum_jem Tue, 09/29/2009 - 23:52
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Previous poster's right about setting static ARPs.

I also have the same implementation in my environment. We configured MS NLB to use multicast and configure static ARPs on the gateways.

There is however, a caveat if you are not running ip multicast-routing. You will have a lot of broadcast traffic(no biggie, but yeah) . I worked around it by configuring static MACs for the NLB pointing to the various ports also.

Hope this helps.


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