what effect will setting NIC Teaming 'Notify Switches' to No have?

[register]

We are trying to use Microsoft NLB to create an Exchange 2010 CAS cluster.

However, we have a scenario where win2008+Exchange2010+vmware+Cisco65xx will not support multicast NLB.  Older Cisco 3700 switches will, but this is not practical as our VMware hosts are connected to the Cisco 6509s.  It also works with physical servers. It also works with win2003.  Glad we have invested in all this new technology.

Anyway, aside from switching to physical servers, the only way around this is to switch to unicast NLB.  For unicast, VMware recommends changing the Notify Switches setting in NIC Teaming to No to prevent RARP packet transmission. What effect will changing this setting have?  Has anyone made this change?

thank you

[chriswahl]

Turning off "notify switches" will prevent the host from updating the mac table of the switch on behalf of the VM in the event of failure or a vMotion.

If a VM becomes reachable on another port, it will need to inform the switch of its new location so that the mac table is updated. Since a VM doesn't know when it moves around (It's ignorant to this fact) it can take some time before the switch realizes where the VM has moved. This can cause network interuption.

I typically isolate the traffic that needs this to a specific port group so to avoid adversely affecting other VMs.