EXCH2013 with DAG and Loadbalancer

Posted on 2016-11-03
Last Modified: 2016-11-07
Hi Experts,

with the old version of EX2007 we used the windows internal loadbalancer NLB on both HUBCAS servers.

With EX2013 I can create a DAG but this is just for mailbox DB redundancy.

My new EX2013 servers are installed as MULTIROLE server, with MBX,CAS,HUB role.
How to distribute the traffic through all HUBCAS servers ?
Question by:Eprs_Admin
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LVL 41

Expert Comment

ID: 41872803
You need to place HLB in your environment for HA for CAS role. MBX DAG is enough. NLB is not recommended.
ID: 41873066
Create round robin through internal DNS.  Some people will say that its not efficient, but it does work.  I have 1 domain environment, and 2 EX servers.  Create new ZONE with your SMTP address.  E.g.  Add two HOST A records. One for EX1 and another for EX2.  
Create your DAG quorom or "Witness directory" and give it its own I.P address.  

We have a smaller environment of 300+, but I can tell you from experience, that if failover occurs it is less than 5 minutes for email to be connected back to the users from the passive EX server and becoming the active server.
LVL 41

Expert Comment

ID: 41873373

Pls tell me, if exchange service not responding...will your dns round robin will failover to second server?

Author Comment

ID: 41873567

that means I cannot use WNLB in my EX2013 environment.
For now I have no hardware loadbalancer.
I have my hardware firewall. This firewall has also the feature for balancing traffic.
But this is just from external to internal.

Author Comment

ID: 41873838
So WNLB is not recommended ?
But hardware load balancer from my Firewall is ok ?
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ID: 41874542

Yes to your question. If you are asking if my EX1 is shutdown, it fails over to EV2, every time.
LVL 41

Expert Comment

ID: 41874594

I didn't asked shutdown, I asked service not responding. What happens then. Does your Round-robin failover.
ID: 41874671
That I don't know.
LVL 41

Assisted Solution

Amit earned 250 total points
ID: 41874757

No problem...

Here are the primary reason for not using or recommend DNS round-robin:

 1) Monitoring: How you are going to monitor DNS Round-Robin for any issue.
 2) You cannot distribute load using DNS RR.
 3) With DNS RR Active/Passive setup not possible.
 4) No reporting
 5) DNS RR is not application aware solution, so if Exchange server is down, client might still be connecting to failed server.

 HLB is must requirement for Exchange. I known it add extra cost to the overall setup, however MS recommended to use HLB.

Accepted Solution

get-ADuser -F ($_.Name -eq "Todd") earned 250 total points
ID: 41874898
Yes Amit,

I have definitely heard of those exact reasons that you have mentioned.  I also proposed a HLB that was around $2500.00.  Mostly because of worrying about what you said,  Not able to be application aware.  But because of the expense of Exchange plus Veritas Enterprise Vault, that is on the back burner.

@ Eprs_Admin

From a best practice standpoint I cannot dispute what Amit has.  My environment is only 300+ users and I am the AD admin and Exchange Admin.  Because of this I am constantly aware of what is going on.  I can say that if one of my EX Servers is "out"  the other seems to kick on fairly quickly.  But only if the system is shutdown.  I cannot say that if any of the other situations that Amit has stated above, that it would give the same result.  HLB's are much better than RR. For now it works fine for us.

Author Closing Comment

ID: 41876698
Thanks first of all I will go for RR and next year I go for a HLB.

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