CAS array on different network

I am not sure this is possible or not.  Can I create a CAS array by creating 2 CAS servers on 2 different Networks on 2 different AD site, or this is out of the question?
FundFireAsked:
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Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
The only automated way is to have a load balancer.
This isn't an Exchange issue, but a DNS issue. There is no availability in DNS, so if you have both IP addresses in the DNS record then all you get is round robin and a confused Exchange server.

Therefore if you want completely transparent high availability the only option is load balancers, or you bring your external traffic in via the second site, and it goes over an internal link.

Simon.
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Simon Butler (Sembee)ConsultantCommented:
CAS Arrays are AD site specific.

So while you could have a single CAS Array across two sites (not advised though), if you have them in separate AD sites then you cannot have them in the same array.

This is a good thing, as it allows you to control where the traffic goes. Autodiscover is also AD site aware.

Simon.
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FundFireAuthor Commented:
Got it.

Here is my problem though.  I point the webmail to specific server located in Network A.  When the databases moved to another site for some reason to network B;  I have a CAS box in that location.  That takes care of my Outlook users.  They get a message on Outlook that they need to relaunch and all is well.  But my Webmail goes down because it is pointing to specific server on Network A.  I have to go manually change the IP address of Webmail to get it working again.  I really don't want to do that and I don't know how to solve this issue.
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Simon Butler (Sembee)ConsultantCommented:
If you have mailboxes in Site A and you failover to Site B, then you need to ensure that the CAS role holder in Site B does NOT have an external URL configured.
That way CAS will proxy the traffic.
If you do have an external URL configured it needs to be different to the main server. Exchange will then redirect the users.

You need to look at the proxy/redirection TechNet Article to get the configuration correct.

The CAS Array address should be unique to the CAS Array and used internally only. It is only for Outlook MAPI traffic.

Simon.
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FundFireAuthor Commented:
Thanks I will look into this.  I let you know if something comes up.
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FundFireAuthor Commented:
Hi Simon,

What if my CAS box on site A goes down completely which holds the external URL.  All users are in site B now and they all point to Site 2 CAS box which does not have external URL configured, how the users are going to get to Webmail?
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