Exchange 2013 Setup Need some clarification

Chris Fletcher
Chris Fletcher used Ask the Experts™
Ok so before I ask my questions, I'm going to briefly list how I've got things setup.

I've got 3 servers, all running MS Windows Server 2012 R2 Standard

2 of those servers, lets call them MAIL01 and MAIL02 have Exchange 2013 installed. Both the Mailbox and Client Access roles.

The other server is just the File Share Witness

I've created a DAG and have made MAIL01 and MAIL02 members of the DAG

I have a mailbox database on MAIL01 that I added a copy for on MAIL02

Lets assume I've got the following IP addresses on these

MAIL01 -
MAIL02 -

I also have a Barracuda spam device setup lets assume IP

I am fully aware of how DAG and maintaining QUORUM works.

I am aware that DAG does not provide high availability to the CAS servers.

What I've done is on my domain controller in DNS, I've added 2 A host entries for pointing to and I implemented this because I don't have a hardware load balancer.

I have static NAT setup on my router for the following ports: 80, 110, 143, 443, 587, 993, 995. These all go to IP
I have 2 more ports, 25 and 465 which go to which is the Barracuda. In the Barracuda config, I have it routing all e-mails to which is the DAG.

I have a few questions based on this setup.

1. Is this properly setup for high availability?
2. I'm assuming that in order to provide the same kind of round robin DNS for the CAS server from the outside as I have from the inside, I'd need to have a public IP for each of the CAS servers and add both of those to my external DNS servers. If I do this, which ports would I need to setup static NAT for on my router?
3. Yesterday we had a short power outage which caused MAIL02 to go down. Once this happened, the database on MAIL01 was in a dismounted state and I was unable to mount it again. Things wouldn't start working again until MAIL02 was back online.

Basically what I'm trying to achieve is the following:

Have a single domain
Have multiple exchange servers for high availability so that if one were to go down, the other would still be available.
Continue to be able to use my Barracuda and have it route mails to a single IP address.

Any help with this would be much appreciated.
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Senior Systems Admin
Top Expert 2010
Round Robin DNS isn't necessarily the best solution for handling HA in Exchange, since it isn't app-aware. If one of the exchange servers has issues, it'll cause some clients to be unable to connect properly. The best way to handle Exchange HA is to use a load balancer, but in the absence of that, just configure your address to point to one of the exchange servers and change the record to point to the other if the primary server fails, then re-point the NAT config on the firewall to go to the good server. If you have mailboxes on both servers, the primary server's CAS role will proxy connections to both mailbox roles without any issues, so you don't need to provide users access to the secondary CAS role.

Regarding your power outage, was the File Share Witness still accessible from MAIL01 during the time MAIL02 was offline? If MAIL01 loses connectivity with both other nodes it will force dismount.


Understood. Is there any particular load balancer you could recommend. The boss is pretty particular about wanting to have HA without having to make manual changes.

The other part that I'm confused about is how to go about setting up the Barracuda appliance.

The router is forwarding ports 25 and 465 to the Barracuda.

The Barracuda can only route mail to a single IP address.

I am currently routing it to the DAG IP address, this seems to work. Is this the proper way to do it or should I be using a load balancer?

The File Share Witness was still accessible during the outage.
Adam BrownSenior Systems Admin
Top Expert 2010
The DAG IP isn't supposed to be used for anything, really. If you get a load balancer, you can configure it to balance SMTP traffic as well. Kemp balancers are pretty good and relatively inexpensive, and have templates for Exchange 2013.
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