Understanding CAS Array On Exchange Server 2010

CAS Array On Exchange Server 2010

Client access Array provides a virtual name that a single access point to all the Exchange Server 2010 CAS servers in Active Directory. With the architectural changes in Exchange 2010 that almost other things, introduces the new RPC Client Access service (which moves Outlook MAPI mailbox connections from the back-end Mailbox servers in the data tier to the Client Access servers (CAS) in the middle tier) providing both a load balanced and highly available Client Access Server (CAS) solution is even more important than was the case with previous versions of Exchange. CAS array is active Directory object and lInked with RPC CAS Services and DNS recrod. this record will be the virtual record associated with IP address.  In on site there will be only one CAS array created , we can not span with another AcitiveDirectory Site. Here is then topic come for Exchange DR, with another site create another cas array, add associated same site CAS server and while DR, flip the IP , DR done 🙂 how easy is that right.

Remember,  CAS array is only for RPC endpoint not for HTTPS connection Like owa, outlook anywere or activeSync and CAS array Name should not be included in SSL certificate. FQDN of CAS Array does not need a cert, because it takes only MAPI traffic.

Before moving to create CAS array see at if we have created Database already if not then RPCClientAccessServer attribute of the database will be set automatically to CasArrayName. if we have created database before creating CasArray then the RPCClientAccessServer attribute value would the CAS Server fqdn name in a single CAS scenario 

It is recommended to create a CAS array even if you have one CAS server.

To Create a Client Access Array Follow the steps below:

In article I’ll show you how to create the CAS Array using Network Load Balance feature in Windows Server 2008.

Note: If your CAS servers are virtual machines I’d recommend you to use DNS Round Robin and not NLB on the virtual servers.

The steps to complete this are as follow:

  1. Create DNS A record for the CAS Array and the NLB cluster
  2. Install NLB
  3. Create the CAS Array using Exchange Shell
  4. Point Mailboxes Databases to the CAS array


Create DNS record for the CAS Array Hostname using DNS manager, in this example I used:


Install NLB by using PowerShell, This is valid if you are Windows Server 2008 R2 if not use the GUI.

Import-module servermanager

Add-WindowsFeature nlb

Now we will configure the NLB cluster.

Open NLB Manager -> Cluster -> New

Type the First Host in the CAS array cluster and Click Connect.

(It the example I have 2 CAS servers)

Here we can set the Priority of the node.

In this Screen we add the Cluster IP address that we created the A Record for.

In the Cluster Configuration screen set the Operation mode to Multicast and Set the Cluster Hostname is Full Internet name:

Click Finish

Now we need to add the Second CAS server.

Right Click on the NLB cluster and Click on Add Host To cluster.

Follow the Same steps for the first node.

Create CAS Array using the cmdlet below and make sure you are using the correct Active Directory site name.

New-ClientAccessArray -fqdn mail.test.local -Site “default-first-site-name” -Name mail.test.local

Next we will link the CAS array to the Mailbox databases.

Get-mailoboxdatabase | set-mailboxdatabase –rpcclientaccessserver mail.test.local

You can also set the settings to a single mailbox database using

Get-mailboxdatabase name –rpcclientaccessserver casname

All Outlook Clients will connect to the CAS array next time they start Outlook.

Few point we need to make a note.

  1. A CAS array object does not load balance your traffic
  2. A CAS array object does not service Autodiscover, OWA, ECP, EWS, IMAP, POP, or SMTP
  3. A CAS array object’s fqdn does not need to be part of your SSL certificate
  4. A CAS array object should not be resolvable via DNS by external clients
  5. A CAS array object should not be configured or changed after creating Exchange 2010 mailbox databases and moving mailboxes into the databases
  6. A CAS array object should be configured even if you only have one CAS or a single multi-role server.


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