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Exchange 2013 SP1 Round Robin question

Posted on 2014-03-27
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Last Modified: 2014-06-06
Hi

I've been reading many articles concerning round robin recently.  But I'm not sure to fully understand.  Here is my understanding.  

- the external DNS must me configured as such:
mail.contoso.com    A    <IP address of EX1>
mail.contoso.com    A    <IP address of EX2>

- in the event that a server goes down, it can take up to 20 seconds to get another connection (Outlook 2013, ActiveSync, OWA)

But I see nothing about the internal DNS.  In order to access OWA locally from mail.contoso.com DNS records have been added in the local DNS.  Is it something we should not be doing?  

Thanks
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Question by:quadrumane
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by:Md. Mojahid
Md. Mojahid earned 250 total points
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Round Robin doesn't really help with a CAS Array. If one of the servers goes down, then the DNS will continue to send clients to that host because has no awareness that the server is down. I don't see how you say that it works fine. You really should be using at least WNLB so that there is some server availability awareness, or you are going to need to have a process to remove the down host from DNS - which could take some time depending on when the failure occurs.

http://blogs.technet.com/b/networking/archive/2009/04/17/dns-round-robin-and-destination-ip-address-selection.aspx

http://technet.microsoft.com/en-us/library/cc787484(v=ws.10).aspx
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by:quadrumane
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Simon Butler (Sembee) earned 250 total points
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Both of those articles are flawed.
Round Robin does not provide any kind of load balancing or availability, because DNS doesn't do that. You are dependant on the client doing another DNS lookup, nothing to do with Exchange.

The only way that may work is to have two unique URLs for both servers so that if one goes down the other is found via Autodiscover.

Ultimately though a hardware load balancer is required, and there isn't really any other choice for high availability of the client access functionality.

Simon.
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