CAS Proxy issues with Exchange 2007 & Exchange 2003 Coexistence

Today I’m going to tell you about an issue I had with an Exchange 2007 CCR implementation.

The scenario includes:

1) The new environment:
1 CCR Cluster – based upon server 2008
2 HUB/CAS Servers – based upon server 2008
2 ISA 2006 Servers in NLB

2) The legacy production environment:
1 Exchange 2003 cluster – based upon windows w2k
2 Front-Ends servers

I’ve started testing pilot mailboxes and operations, all seems to be working great regarding the new environment functionality.
When I tested connectivity with mailboxes residing in the 2003 Back-End cluster using the new CAS servers I’ve encountered errors.
1 – Error 404 , using /exchange to a 2003 Back-End mailbox.
2 – Error 500 , using /exchange to a 2007 Back-End mailbox.

In addition . an Event ID 1000 , with source EPROX was logged in the CAS servers application log, the description didn’t make much sense..except that it specified the Back-End cluster 2003 name.

” The description for Event ID 1000 from source EXPROX cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer. “
If the event originated on another computer, the display information had to be saved with the event.
The following information was included with the event:

After troubleshooting we came to the following solution :

2 -The error 500 was because the CCR Cluster servers were missing the following Prerequisite : Web-ISAPI-ext , making sure all Server 2008 prerequisites for CCR mailbox role were installed solved that.

1 – The Error 404 was issued because the new CAS servers FQDN were not included in the Default Web Site host headers. this KB apply here because we have 2 new 2007 Front-Ends, our CAS Servers.

Read also more about the concept of Coexistence in regarding OWA in Technet:
Outlook Web Access and Exchange 2007, Exchange 2003, and Exchange 2000 Coexistence

Troubleshooting highlights in Coexistence:

1) First check that using /Exchange to the CAS servers with mailboxes in the 2007 Back-End.

2) Do not change the Default Authentication methods for any Virtual Directory of Outlook Web Access in the Client Access , under Server Configuration.

3) If your 2003 Back-End server is running Windows 2000, Make sure you are adding ALL the host headers you will use (eg;, owa.local.dom etc..) Follow “How to configure host header and authentication information in Exchange 2000 Server or Exchange Server 2003 Outlook Web Access on a Windows Server 2003 or Windows 2000 server cluster”

4) You should not see any EPROX errors in applications log , nor Availability Service errors that actually say that the CAS server cannot find / access your Back-End servers.

5) IIS Logs are your friends !! use them. make sure the requests are getting to the correct Virtual Server / IIS Website.

6) Read the Technet guides ! again.

Hope this helps!

What do you think about this post?