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Questopn about Exchange 2010 CAS.

I am studying for my Exchange 2010 certification and worked with Exchange 2010 Implemntation last year. I slightly remember there is something different in the way CAS acceses the mailbox server in 2010 than 2007. Can someone help me with this?
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355LT1
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Shabarinath RamadasanInfrastructure ArchitectCommented:
Major Difference - Previously with Exchange 2003/2007, Outlook clients directly connect to back-end/Mailbox server for MAPI communications. With Exchange 2010, Outlook client directly connects Client Access Server. This makes very much sense as Client Access Server can easily route traffic to appropriate mailbox server.

Cheers
Shaba
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Shabarinath RamadasanInfrastructure ArchitectCommented:
In Microsoft Exchange Server 2007, the Client Access server role was introduced to handle incoming client connections to Exchange mailboxes. Although the majority of types of client connections were made to the Client Access server, Microsoft Office Outlook still connected directly to the Mailbox server when it was running internally with the MAPI protocol.

A new service was introduced with Exchange Server 2010 to allow these MAPI connections to be handled by the Client Access server. The RPC Client Access service provides data access through a single, common path of the Client Access server, with the exception of public folder requests, which are still made directly to the Mailbox server. This change applies business logic to clients more consistently, and provides a better client experience when failover occurs.


In addition to moving processing of incoming Outlook Mailbox connections to the Client Access server, in Exchange 2010, directory access is also handled by the Client Access server. For more information about directory access, see Understanding the Address Book Service.

Microsoft Outlook still connects directly to the Mailbox server to access Public Folder databases. If a client tries to connect to a Mailbox server for public folder access, the RPC Client Access service (MsExchangeRpc) answers the RPC endpoint. If the endpoint is on a server that has the Mailbox server role installed, the RPC Client Access service will only allow public folder logons and will provide a referral to a Client Access server or a Client Access server array. If the endpoint is on a Client Access server or Client Access server array, it will allow only Private folder logons and will provide a referral to a Mailbox server for public folder access.
 Advantages of the RPC Client Access Service

There are a number of advantages to the RPC Client Access service. Clients encounter less downtime during a mailbox failover, because all connections are made through the Client Access servers. When failover occurred in Exchange 2007, Outlook clients would be disconnected from the Mailbox server for a period of time that depended on their network configuration. In Exchange 2010, if a single Client Access server in a Client Access server array fails, the client will immediately be redirected to another Client Access server in the array. If a Mailbox server that is part of a Database Availability Group (DAG) fails, the client is disconnected for only the amount of time it takes for a failover database to be mounted.

A load-balanced array of Client Access servers lets you spread the traffic load over all Client Access servers in the array equally.

Other problems resolved by this new architecture include the following:

    Some issues with messages displaying differently on different clients.
    Problems uploading certificates to the global address list.
    The inability to create profiles for hidden users.
    Inconsistent application of business logic to clients.
    Public folders connecting to the RPC Client Access service on the Mailbox server, rather than the Client Access server.

Additionally, the DSProxy service has been removed and the new Address Book service is responsible for updating certificates and distribution list membership and maintaining delegate information for Outlook clients.
 MAPI Client Connections

In Exchange 2007, Outlook and other MAPI clients communicated with the Client Access server for HTTPS connections such as Exchange Web Services (including the Availability service and Out of Office settings), and Offline Address Book downloads, but communicated directly with the MAPI RPC component on the Mailbox server and the NSPI endpoint on Global Catalog servers for Directory Service inquiries.

In Exchange 2010, these connections are made to the MAPI RPC connection point on the Client Access server or the Client Access server array.
 The Address Book Service

In previous versions of Exchange, DSProxy, a referral service that told Outlook clients where to find the Name Service Provider Interface (NSPI) endpoint, was responsible for directing Outlook to a global catalog server. DSProxy was located on the Mailbox server. DSProxy has been eliminated in Exchange 2010 and replaced with the Address Book service.

Currently, when an Outlook client makes a request of the Client Access server, it results in one of two possible actions.

    If the user's mailbox is on an Exchange 2010 Mailbox server, then either the request is handled by a Client Access server in the current Active Directory site, or if the user’s mailbox is in a different Active Directory site, the request is proxied to the destination Active Directory site.
    If the user's mailbox is on a legacy Exchange Mailbox server, the directory request is referred to the user's Mailbox server. Legacy Mailbox servers can't communicate directly with Exchange 2010 Client Access servers for directory information.

The Address Book service also provides information about writable domain controllers as well as global address list access. For more information about the Address Book service, see Understanding the Address Book Service.


In addition to the RPC Client Access service, Exchange 2010 introduced a new logical structure to the Exchange organization: the Client Access server array. When a Client Access server array is defined in an Active Directory site, it serves as a single contact point for all client connections within that Active Directory site. A Client Access server array can include one or many Client Access servers.

Each Active Directory site can have a single Client Access server array. A Client Access server array doesn’t provide load balancing. A separate load balancing solution is still needed. For more information about load balancing, see Understanding Load Balancing in Exchange 2010.

We recommend that you create a Client Access server array even if you only have a single Client Access server within your organization. When a Client Access server array is created, clients connect through the virtual name of the Client Access server array rather than directly to the fully-qualified domain name (FQDN) of your single Client Access server. If a single Client Access server needs to be replaced within an Active Directory site or a second Client Access server is added, no profile updates are necessary on the clients.

After a Client Access server array is defined within an Active Directory site, all Client Access servers within that Active Directory site are automatically part of the Client Access server array.

Source - http://technet.microsoft.com/en-us/library/ee332317.aspx

Shaba
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