Sunday, January 5, 2014

Exchange Server 2010 -Configuring Client Access Array - Part-1

With Exchange 2010, Outlook MAPI clients use the Client Access Server (CAS) role in the middle tier as the RPC endpoint, which has resulted in this role being even more critical than in previous versions of the product. Because of this, all organizations should consider making this role highly available by introducing multiple CAS servers in each Active Directory site as well as load balance the protocols and services provided by this role.

There are lot of architectural changes in Exchange 2010 that amongst 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 in the middle tier) providing both a load balanced and highly available Client Access Server solution is even more important than was the case with previous versions of Exchange.
If Organization do not plan to deploy multi-role Exchange 2010 servers Windows Network Load Balancing (WNLB) technology is good choice.
If you plan to deploy multi-role Exchange 2010 servers with both DAG protected mailbox databases and load balanced/highly available CAS server service, you cannot use WNLB due to Windows Failover Cluster (WFC) and WNLB hardware sharing conflicts.

When a hardware load balancer based CAS array has been properly configured, all servers in the array are represented by a single virtual IP (VIP) address and a fully qualified domain name (FQDN). When a client request comes in, it will be sent to an Exchange 2010 CAS server in the CAS array using DNS round robin distribution method.
Microsoft does not recommend more than 8 nodes in a WNLB based cluster due to scalability and functionality limitations.

Preparing for NLB
once two or more Exchange 2010 servers (each server 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.  Please note that the IP address should be on the same subnet as the two CAS servers that will become members of the NLB cluster.

NLB can be configured either in unicast or multicast mode.  The former changes the MAC address of each NLB cluster member’s NIC to a virtual cluster MAC address, to which clients connect.  The latter allows the NICs to maintain their existing MAC addresses and adds a virtual cluster MAC address. 
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 “Primary” (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.

Once the NICs have been configured, we must ensure that the binding order is configured to bind the Primary NIC first.  Within the Network Connections window, click Advanced, Advanced Settings and modify this if necessary. 

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