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Exchange Server 2007: How CAS Proxying works for Outlook Web Access (OWA)

I wanted to go into explaining how Exchange Server 2007 CAS Proxying works for Outlook Web Access (OWA).

Proxying for Outlook Web Access is used when there is only one Internet-facing CAS Server. In this scenario the will be proxied to the CAS server where his mailbox server is located. This requires more intensive resource on the CAS server than doing redirection. The main benefit to this is your users can have a single point of access from external and proxying is transparent to the end user.

CAS-CAS Proxying is quite similar with the process described in the future topic “How CAS proxying works for ActiveSync”. There are a few differences regarding the errors and logs.

Please see the following flowchart that will help you understand this process. To view the full version, please click on the thumbnail. We wanted to publish the flowchart in high resolution:

1. The First CAS queries the Active Directory to determine the location of the user’s mailbox and the version of Microsoft Exchange that is installed on the Mailbox server. If the mailbox is on Exchange 2007, the First CAS will determine the best CAS, a Client Access Server in the same AD site as the user’s mailbox server.

If the user’s mailbox is on an Exchange 2003 server, the request will be proxied directly to the destination Exchange 2003 back-end server, even if there is an Exchange 2007 Client Access server within the destination Active Directory site. Windows Integrated authentication is required on Exchange 2003 /Exchange virtual directory.

Once is determined where the user mailbox is located, in this case on a Mailbox Exchange 2007 Server named Chicago.fourthcoffee.com. The First CAS has already made the decision to talk directly to a mailbox server in the same site, proxy the request to the Second CAS or return a web page link with the ExternalURL from the Second CAS where the user mailbox is located.

As the mailbox is on an AD remote site, the request is proxied to the Second CAS named Dallas.fourthcoffee.com.

Full Article

Microsoft, Exchange Server 2007, CAS, Proxy, Outlook Web Access, OWA, Client Access, Tutorial, Knowledgebase, Article

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