Hello all! My company has deployed an Exchange 2010 environment with multiple CAS and Mailbox servers using DAG and the Microsoft network load balancer. The CAS Array fails to work when the CAS servers span multiple switches. The CAS servers are VMs connected to a virtual switch which has redundant connections to two separate switches. It is your typical design for redundant hardware. The CAS array does not work when the multiple switches are spanned though. Our network engineers are asking for documentation that clearly states that the CAS array is supported to span multiple switches in a redundant design as part of their troubleshooting the issue. Anyone know of a document that has this? I know that I have seen plenty of MS docs that show this exact same design, but nothing that says "A CAS array can work with multiple switches feeding into it." Thanks for any help that you can provide!

VM and NLB have specific requirements based on unicast or multicast. See http://www.vmware.com/files/pdf/implmenting_ms_network_load_balancing.pdf

Any update on the issue?Gulab | MCITP: Exchange 2010-2007 | Skype: Gulab.Mallah | Blog: www.ExchangeRanger.blogspot.com

I would suggest turning this around on it's head and pointing out there is nothing that states that NLB (what we're really talking about) is restricted to utilising a single switch. It certainly can work, and I've seen it work in operation, under load, across multiple core switches between data centres without issue. It almost certainly sounds like a misconfiguration at the network layer. The document LMurphy links to should have some information about network configuration that may need to be configured for static ARP entries, and the network vendor may be able to provide information about specific issues and relevant configuration your network engineers may need to perform on their equipment. Also, if you haven't tried it already, it may be worth testing NLB against a single switch (using separate physical ports on your hypervisor host) SteveSteve Goodman Check out my Blog for more Exchange info or find me on Twitter