Exchange CAS 2010 and NLB: Unicast or IGMP Multicast


Can someone please advise on which mode to use for a 2 exchange environment please.

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Exchange_ImranConnect With a Mentor Commented:

Unicast or Multicast Mode?

A Windows NLB array can be configured in either unicast or multicast mode. Since WNLB is not something Exchange administrators or consultants deal with on a daily basis, it can be difficult to decide which mode to choose when time comes to load balancing the RPC traffic to the RPC Client Access service on the CAS servers in the Exchange 2010 infrastructure.

Unicast Mode:

With the WNLB cluster configured in unicast mode, the MAC address of each server’s network adapter will be changed to a virtual cluster MAC address, which is the MAC address that will be used by all servers in the Windows NLB cluster. When unicast mode is enabled, clients can only connect to the servers via the VIP address on the network interface card (NIC) that has been configured with the cluster MAC address.

Multicast mode:

With the Windows NLB cluster configured in multicast mode, a multicast MAC address is added to the cluster adapter of each server in the cluster. Note that I write “is added”, as each server will retain their original MAC address.

A Windows NLB cluster, no matter what mode it is configured in, works with just a single network adapter installed in each server, but it is recommended to install a second network adapter in each server, in order to achieve optimal performance, and to separate ordinary and cluster related network traffic.

So what mode should I use for my Exchange 2010 CAS array and how many network adapters should I install in each Client Access server? Well, a best practice recommendation is to install two network adapters and use unicast mode, so that the host and cluster network traffic are separated on their own respective network interface. However, if you only have the option of installing one NIC in each CAS server or if you’re forced to using multi-cast mode because of the switches used in your organization, you should pick multicast mode.

Imran Shariff
lawlibraryAuthor Commented:
Thanks makes sense
Senior IT System EngineerIT ProfessionalCommented:
Does  this rule also applies for the VMware Virtual Machine deployed Exchange Server ?
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