Exchange 2010 DAG across 2 pyhsical sites but 1 'AD-Site-Name'

We have two mailbox servers on one site and 2 mailbox servers on another site.(Two physical sites). All 4 servers are under 1 'AD-Site'. However the primary site is on a different subnet than the seondary. Can we still use MAPI and Replication NICs and have replication data routed across dag.
Also if we use a hardware loadbalancer can we have an active/active setup on the two sites?
Thanks
jazmanuniAsked:
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Adam FarageSr. Enterprise ArchitectCommented:
This comment bothers me a bit...

All 4 servers are under 1 'AD-Site'. However the primary site is on a different subnet than the seondary.

The short answer is yes, this would work. You are just assuming particular risks.

- The Mailbox / HUB / CAS role will assume all DC are local, as they are within the same subnet (e.g: local site) and will simply use any DC (instead of the local within that physical site) for lookups. This causes LDAP querying issues and performance issues for Exchange, which your users can see.

- A CAS Array (the HA portion of the Client Access role) assumes all CAS within the same subnet are within that local, physical site. Meaning you are now doing cross site traffic, thus causing issues when doing a DR scenario (if / when a datacenter fails)

- You are going to have serious issues with datacenter switch-overs (http://technet.microsoft.com/en-us/library/dd351049%28v=exchg.141%29.aspx)

These are just to name a few that come right off my tongue / brain.

Once again, this can be done but it would be a lot easier to correct the topology and create two different AD sites within AD Sites and Services. Segregating your AD sites will allow for proper mailflow, LDAP lookups and true HA / DR.
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Adam BrownSr Solutions ArchitectCommented:
The big question you should consider is how much latency and bandwidth do you have between your physical sites? If you are above 100ms latency going between physical sites, you will probably run into issues with a physically stretched DAG (pretty much everything mentioned above). However, if you have a low latency, high bandwidth link between sites, you should be perfectly fine with the configuration you want, and you can use Active-Active setup as long as your Load balancer supports physical site redundancy. Just note that you wouldn't run your MBX servers through the load balancer. Only CAS/HUB.

Failover isn't really such an issue as was mentioned in your configuration as long as you have DAC enabled in your environment (Look up Datacenter Activation Coordination). That greatly simplifies the failover process in the case that one physical site goes down entirely.
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jazmanuniAuthor Commented:
Thanks
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