Will this setup failover the CAS correctly?

I am trying to plan my second Exchange 2013 install, it will be a single server hosting both the mailbox and CAS roles. The first exchange server is working just fine. What I want is that the second server can take over if the first site gets struck by an asteroid.

I put together a real quick diagram to help you see what I am thinking of, I got this basically from a couple of cbtnuggets videos I've been following. Let me know if clients external and internal can failover to either of the CAS boxes. I will eventually create a DAG between the two, but I'd like to setup the CAS failover first.

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internetworksAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
Based on the diagram you are trying to load balance this using DNS? Using 1.1.1.1 for AD Site1 and 2.2.2.2 for AD site2 will not work. You need to use a hardware load balancer which is the recommended approach.

Simply using DNS will not fail-over your CAS servers. Also you cannot fail-over CAS servers in different sites, this only works for DAG and mailbox servers. You need to have 2+ CAS servers in each site and then create load balancing between them for each respective site where you will be hosting Exchange.

CAS server is required in every site and if you only have 1 CAS server setup in either site, if it fails Exchange will no longer be able to connect you to your mailbox as it uses persistent connections.

So have multiple CAS servers per AD site, then use a hardware load balancing solution to have high availability.  You need to use Windows Networking Load Balancing (at a minimum) to have high availability and this method is not recommended for production environment.

Will.
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internetworksAuthor Commented:
Hello,

Will, thanks for the great input, I appreciate it. So does that mean it will not failover internally and externally? I just assumed if Site 1 goes down that external client will eventually just pull up the new mail.company.com IP address and be on their merry way.

What could you recommend for my current situation. All I have is two servers (no budget for anything more) at two different locations with both CAS and MBX roles. Basically what my goal is, is that if one server goes down my clients can still access their email from outlook or owa
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Will SzymkowskiSenior Solution ArchitectCommented:
Externally only affects the internet facing site. If they both are internet facing then you will have 2 different external URL's one for each. Having this configuration with only 1 CAS in each site will not get you high availability.

The only suggestion for HA for CAS in your situation is to move your Exchange environment to Site1 or whatever site is internet facing.

From there you can set both CAS servers up using a hardware load balancer. You can then have users from Site 2 just retrieve mail across the WAN rather than locally.

You will then need to ensure that you have redundant WAN for Site2 incase your primary link fails.

Just note if you want to proceed with this method you will also have to move all of your mailboxes to Site1 as well. Your Exchange environment in Site2 will no longer be used.

Will.
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internetworksAuthor Commented:
So that does make sense, but what I can't understand (and hopefully you can clarify for me) why a DNS round robin of mail.company.com point to my site 1 and site 2 (both internet facing) CAS boxes will not work. Can they not both respond to that request?
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Will SzymkowskiSenior Solution ArchitectCommented:
When you set this up you do not use the same name space for 2 internet facing CAS servers you use 2 different ones. you would use mail.domain.com for Site1 and mail2.domain.com for Site2. These would have different IP associated with them and the user would manually enter the URL for whatever Site they belong to.

Even if one of your CAS boxes was to go offline you could connect to the other SIte that is online and it would proxy your connection to your mailbox in the proceeding site. Well in this case it wouldn't because your CAS server would be offline in this scenario. So it will not work.

Hopefully this answers your question. Also another note you should not have 2 different Auto Discovers. You should only need one autodiscover per FQDN (Active Directory Forest).

Will.
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internetworksAuthor Commented:
Thanks for helping, wish I could give you more than points.
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Will SzymkowskiSenior Solution ArchitectCommented:
Not a problem. Glad to help. If you need any questions you want me to participate in, in the future just follow me and send me a message with the link and I will do my best to answer it.

Will.
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