BIG-IP LTM for Exchange 2010 HUB/CAS load balancing (Single vs Dual NIC)

Hello Sach2910-

Presumably your CAS/Hub and mailbox servers are on different subnets; if they're on the same one, obviously, the default gateway (or static routes) doesn't matter for inter-server/inter-role communication, since all communication is local. That probably should go without saying but I wanted to put it out there just in case.

Once that question is out of the way, here's one important caveat: by default, a BIG-IP does NOT route traffic. So just defining one of a BIG-IP's self IP addresses as a default gateway isn't enough to enable inter-subnet communication. There are a couple of ways to do this; by far the most-preferred is to create two 'Forwarding (IP)' virtual servers (one per subnet), of type 'Network', and 'All' selected for Service Ports, then specify the destination subnet and mask in each, with no Source Address Translation (SNAT) enabled. BIG-IP will operate like a standard L3 router for those subnets, assuming it has an interface on each. [You can restrict traffic sources in the virtual server configuration if you want to limit the overall routing to just those two source networks, or even specific hosts.]

Please let us know if you have further questions.