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Exchagne 2013 DAG Questions

We are looking into setting up a DAG with our exchange 2013 server and I just have a few questions I'm hoping someone familar with this can answer for me.

1. Can a DAG provide CAS redundancy in addition to the database availability it provides? If EX1 fails will all our users inside of our network on outlook automatically switch to EX2? I've seen some things about needing a load balancer for providing redundancy for the CAS, is that true?

2. When we setup the second exchange server to create our DAG, there is nothing specific we have to do correct. Should be as simple as installing exchange on the server and then following the DAG setup articles out there?

I think really though my main question is the first one. I understand that if I have a failure on one of my exchange servers, I'll have to update my external DNS (or create something such as mail2.mydomain.com) that points to the second exchange server. But do I need to do anything to facilitate the fail over internally with the outlook clients or will they pick up the new server automatically?
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8/22/2022 - Mon



for internal CAS redundancy, you can even pass without NLB or some load balancer, since if you configure OutlookAnywhere to use single name (like mail.domain.com) then in case one CAS server goes down, Outlook clients will automatically, after 20sec, try to connect to another CAS.
20 sec is not much, so there is a high chance no1 will notice CAS is down.

As for external, as Amit said, you need NLB or load balancer. Without it, if one CAS goes down, you would need to reconfigure router to point SSL port to another server.


We already use a mail.domain.com for internal and external connectivity, so since I do that, when i install the second server, I'll simply use the same outlook anywhere name (mail.domain.com) for the setup of that server and then add a second DNS entry for mail.domain.com internally that goes to that second server?

Is there something else I have to do in order to make both exchange servers aware that they can respond to mail.domain.com or will they do that automatically?
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James Murphy

As I said, you need a load balancer. It will HLB which will do the failover for you. Secondly, setting up HA is a expensive solution. How many users you have?

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We have about 50 users.

We do have a Barracuda Load Balancer. So we could just use that for this then.

Point mail.domain.com to a VIP on the LB, then have the 2 exchange servers setup behind that VIP on the LB. Then all we have to worry about is failing over the LB to the other side or setting up a second LB to handle that.

So essentially, as long as both of of the servers have the mailbox role and the client access role, the DAG will handle the database failover, and the barracuda LB can handle the client access failover and send them to whichever server us up.

Having both role on save server is recommended. As that reduce admin effort and license cost for extra server. As you already have HLB, you can use it for Exchange also.
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One last question.

Do both the exchange servers need to be on the same SP/CU level's? Or does it matter if 1 server is something like CU8 and the other is CU5?
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