High availability for Exchange Server 2010 Client access to the messaging platform is provided through a combination of capacity and load balancing. Load balancing and fault tolerance to client connections through the CAS servers are available through a combination of Exchange Server configuration and 3rd party network load balancer hardware devices or Windows NLB. Each Active directory site can have only one CAS array assigned to it and all CAS servers in that site automatically become members of that array. The load balancer device will be used to load balance all connections from Outlook and other clients across the CAS Array, the one exception being Public Folder access. Microsoft Outlook will connect directly to the mailbox server that houses the Public Folder database. The CAS Array is represented by an object in AD which can then be managed as a single object.
Once the array value is defined, any new databases created in that AD site will automatically be assigned the array name for the RPCClientAccessServer property.
For your Outlook clients, you can configure CAS2010 to participate in an RPC Client Access Service array:
TCP 6005-59530 (Please refer to Important note below)
Run the following cmdlet to create the Client Access Service array: New-ClientAccessArray -Name outlook.domain.com -FQDN outlook.domain.com -Site “Internet Facing AD Site”
New-ClientAccessArray [-Name <String>] -Fqdn <Fqdn> -Site <AdSiteIdParameter> [-Confirm [<SwitchParameter>]] [-DomainController <Fqdn>] [-WhatIf [<SwitchParameter>]]
Important: It is recommended that directory and MAPI ports are fixed. By fixing the MAPI and directory endpoints, you can greatly reduce the number of ports that need to be load balanced. The MAPI endpoint can be statically configured in the registry and the directory endpoint can be fixed in a configuration file.
To fix the MAPI endpoint, use the following setting in the registry.
HKLM\SYSTEM\CurrentControlSet\ Services\MSExchangeRPC\ParametersSystem\TCP/IP Port [DWORD] is the value for the IP port to use
To fix the directory services endpoint, edit the RpcTcpPort value in the configuration file Microsoft.Exchange.AddressBook.Service.Exe.config for Exchange Server 2010 RTM. For Exchange Server 2010 SP1, use HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\MSExchangeAB\Parameters and RPCTcpPort REG_SZ value..
Any port number can be chosen between 59531 and 60554. For reference, please refer to below article:
Understanding RPC Client Access