Configuring NLB for Exchange 2010 for CAS Load Balancing

Exchange’s dependence on the Client Access Server (CAS) role has increased dramatically in Exchange 2010.  This is because, in Exchange 2010, on-network Outlook MAPI connectivity now connects to a mailbox through the CAS role via the RPC Client Access Service.  As a result, high availability of the CAS role is crucial since any failure of CAS could affect Outlook client connectivity.  For smaller implementations or those where the limitations of native Windows Network Load Balancing (NLB) are not a major problem

You need two or more Exchange 2010 servers (each with two NICs) with the CAS role installed have been deployed, you are ready to start configuring NLB to provide high availability and load balancing.  First, you must allocate a dedicated private IP address and create an associated A record in DNS for the NLB cluster. 

This IP address and name are what clients will connect to and against which the ClientAccessArray will be created.  In this blog post, I will use and casarray.hyper-v.local
To simplify the management of your NLB cluster members, I recommend that you name each NIC’s network connection so that it is easy to understand what function the NIC serves.  For example, as depicted below, I have named the connections “LAN” (used for communication with clients and servers on the network) and “NLB” (used for internal NLB heartbeat).  This process should be repeated on all NLB cluster members.

IP configuration:
Server 1:

Server 2:


Configuring NLB – First Member

On each NLB cluster member, NLB must be installed.  With Windows 2008 R2, this can be completed simply by running the command “ServerManagerCmd -i NLB” via a command prompt.  Once NLB has been installed, launch the Network Load Balancing Manager to continue the configuration process.


To create your new cluster, you can right-click Network Load Balancing Clusters or simply click Cluster, New.  In the New Cluster wizard, enter the name of the first server in the NLB cluster (for example, CHEK10-01) and click Connect.  This will display the available NICs on the server, at which point the NLB NIC should be chosen before clicking Next.


Since this is the first member of the NLB cluster, you can leave the all of the Host Parameters at their default values, as depicted below.  Please note that the Priority value should be configured as 1 for the first member.


Next we must configure the IP address and subnet mask of the NLB cluster, which is the IP address for which we created a DNS A record at the very beginning of this process.  In this example, this would be and, respectively.


For the Cluster Parameters, we want to enter the FQDN of the DNS A record we created at the very beginning of this process (casarray.hyper-v.local).  In addition, Unicast should be selected as the desired clustered operation mode.


I lieve the Port Rules how they are and end with Finish

Let the NLB cluster converge with its first member and you should eventually see the cluster report success.


Now you can proceed with adding your second cluster member.

Configuring NLB – Second/Subsequent Member

After the configuration of the NLB cluster itself and the first NLB cluster member has been completed, you are ready to add additional members.  Provided that NLB has been installed, you can simply right-click on your NLB cluster in the Network Load Balancing Manager and click Add Host To Cluster.

Enter the name of the second NLB cluster member, for example CHEK10-02, and click Connect.  Be sure to choose the NLB LAN NIC and click Next.


On the Host Parameters screen, ensure that the Priority is set to 2 (or as appropriate, depending on how many cluster members you have) and click Next.


Confirm that your port rules are accurate and, if they are, click Finish to add your second NLB cluster member.


Let the NLB cluster converge with the new member and, eventually, it should report success.


At this point, you have an NLB cluster with two members!

Next configure CASARRAY.

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