Microsoft Exchange 2010 CAS Array – Steps and Recommendations

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:

  1. Create a load balancing array for CAS 2010
  2. Create a DNS entry in your internal DNS infrastructure that resolves to the Virtual IP Address (VIP) of the CAS load balancing array.  The DNS entry, for example, could be
  3. Configure your load balancing array to load balance the MAPI RPC ports:
  • TCP 135
  • TCP 6005-59530 (Please refer to Important note below)

Run the following cmdlet to create the Client Access Service array: New-ClientAccessArray -Name -FQDN -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

Comments (18)

  1. Anonymous says:

    After creating the CAS array, what's the URL that the Outlook archieve from the server side? CAS array FQDN or other predefined URLs?

  2. Anonymous says:

    Yes, its CAS array FQDN for mailbox access

  3. Tunsian man says:

    Thank you, this can be a small guide when we plan to configure NLB H/C

  4. Anonymous says:

    We are pleased to announce the RTM availability of version 9.0 of the Microsoft Assessment and Planning

  5. Anonymous says:

    I’ve written a few blog posts now that get into the deep technical details of Managed Availability. I

  6. Anonymous says:

    Recently I was involved in a Private Cloud project and as part of the project, we were migrating some

  7. Anonymous says:

    Recently, we have seen some questions about what the Update-DatabaseSchema cmdlet in Exchange 2013 is

  8. Anonymous says:

    This has been a great new feature added in Windows Server 2012 R2. The possible scenario of the usage

  9. Anonymous says:

    Exchange team has written below blog on the remote connectivity analyzer tests for mail flow testing

  10. Anonymous says:

    Exchange team has released a blog about Office 365 best practices analyzer for Exchange 2013 as below

  11. Anonymous says:

    Exchange team has written a blog about new Exchange Server deployment assistance as below:


  12. Anonymous says:

    After a long wait, the calculator is there. The calculator recommends mailbox and CAS sizing as well

  13. Anonymous says:

    Exchange team blogged about post TMG world. R ead the blog at

  14. Anonymous says:

    Exchange team blogged about OffCAT as below:
    On Friday, July 19, the OffCAT team released OffCAT version

  15. Anonymous says:

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  16. Anonymous says:

    The Exchange team has released the following update rollups to the Download Center. All three releases

  17. Anonymous says:

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