From: James Ventre (messageboard@ventrefamily.com)
Date: Sat Jul 01 2006 - 10:28:50 ART
I'm not trying to bust your chops, but this isn't the right forum to
discuss this. If you want to discuss this offline - I'd be more than
happy to help you troubleshoot this (Sat. afternoon) - but this isn't
related to the CCIE lab.
>Has anyone seen this problem?
The flooding isn't necessarily a problem, that's the behavior. The
servers don't participate in IGMP so the switch can't do any IGMP
snooping to limit who gets the traffic. Unknown unicast, multicast, and
broadcast frames get sent to all ports in the vlan (except the one it
was received on). If you switch to unicast mode of NLB you get a
similar behavior: Hosts connect to the shared IP address (with unicast
mac) ... and start by sending an arp request for the virtual - the
servers in the cluster respond to arp - but never talk on the mac
address inside of the above arp (they only talk on the MAC of their
real IPs) - so the switch can't learn it - so it's flooded.
>Are static MAC entries handled in software (can't be)?
Not that I'm aware of, but a "sh proc cpu" will help you track down this
particular issue.
I generally avoid this flooding by putting any NLB servers in their own
subnet/vlan so no matter what type of NLB you pick any undesirable
flooding only hits devices that are in the NLB. In general, I think
that clients and servers belong in different vlans anyway.
James
Hosking, Darren wrote:
> I've just tried to migrate a customer from a HP 5308 core switch to a
> Cisco 3750G-48 (enhanced) and the performance of Microsoft NLB (to a
> group of terminal servers) was woeful! The servers and clients are in
> the same vlan so multicast routing is not being used (but is on in
> preparation for segmenting the network).
>
> The clients were still on HP edge switches and the servers were moved to
> the 3750 core stack. I added static mac entries for the multicast
> address pointing to the 14 server ports and performance was still bad.
> Without the static mac entries the multicast traffic appears to be
> flooded to all ports on the 3750.
>
> Has anyone seen this problem? Any suggestions?
>
> The HP has a 76Gbps backplane and the 3750 has a 32Gbps backplane but
> this can't be the only factor as the performance was about 10 times
> worse (eg network computer terminal login 30 seconds vs 5 minutes). The
> HP also doesn't require any special configuration apart from turning
> IGMP snooping on.
>
> Does Microsoft NLB actually use IGMP? It looks the the server has a
> normal (ie not class D) IP address with a multicast mac address and
> responds to ARP with the muticast mac address.
>
> I can't believe the 3750 performed so badly!?!?!
>
> Are static MAC entries handled in software (can't be)?
>
> Thanks, Darren
>
> Ps the 3750 is running c3750-ipservicesk9-mz.122-25.SEE1.bin
>
>
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