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Josh_41258's avatar
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Dec 05, 2011

Exchange 2010 CAS Array - 2 Sites

I have a question regarding CAS arrays in 2010.


We have two sites:




* Pair of LTM's at each site


* One GTM at each site


* 2 Exchange nodes per location (CAS, mailbox, etc all on one server)




We have to support RPC/MAPI for our Outlook clients. My question regarding the CAS arrays: According to the documentation, I have to create two CAS arrays - one for each site/location.




I want the wide-IP for the MAPI/RPC related services to be So, I thought I needed to create both CAS arrays with the FQDN of, but apparently you cannot have two CAS arrays with the same FQDN?




Do I need to just create CNAME's named and which point to (the Wide-IP)? Then, use mapi-location1/ as the FQDNs for the CAS arrays?





6 Replies

  • So here is what I have done.. I'm really hoping someone can give me some feedback here that has more knowledge in this area:



    SITE A:



    * Created a CAS array with FQDN of ""



    SITE B:



    * Created a CAS array with FQDN of ""



    On the LTM's at each side there are three VIP's which handle RPC - one for MAPI, one for Address Book, and one for the RPC endpoint mapper. These VIPs are fronted by GTM's at each location, and the Wide-IP for this service is "" Then, I simply created two CNAMEs for "array-siteA" and "array-siteB" to point to "" Therefore, points to whichever site is active at the moment as determined by GTM.



    Does this sound correct?
  • Helen_Johnson_1's avatar
    Historic F5 Account
    Hi Josh,



    Your configuration sounds correct.



    As an aside, what version of GTM are you running?





  • Helen_Johnson_1's avatar
    Historic F5 Account



    I'd test this out, and if you have any trouble, have a look at, using the search parameter of CNAME and 10.0.0.





  • Hi Josh,



    I can maybe see that configuration working, as long as you are strictly running in an active/passive setup. Otherwise, if you were ever to activate individual database copies in Site B (active/active), you would not have the flexibility of forcing client connections to the respective CAS array for that site.



    The only other concern I have is if you are doing Kerberos authenitcation to the CAS array. I'm not sure if anything will break if the Outlook client obtains a ticket for, but is then redirected to, if that will break anything in the Kerberos authenication process. It may not be a big deal if you are not using Kerberos, but something to be sure to test, if you are.



    The proper way to achieve this, I think, is to have separate CAS arrays for each site with separate namespaces, and as a part of the datacenter switchover process, update the DNS A record for the CAS array in Site A to point to the same VIP as the CAS array in Site B. I realize this makes a datacenter siwtchover a manual process, but per Microsoft, datacenter switchovers in Exchange 2010 are not automatic.



  • Adam,



    Thanks for the advice. I do see what you are saying about active/active scenarios and how this would present a problem. For us, siteB is purely a DR site. There will be no active mailboxes on this site unless siteA is unavailable.



    I do feel like this is somewhat of a "hack," but I'm about to start testing, and I'll report back here with results.