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Exchange Server 2010 NTLM and reverse proxy issues when using Hardware Load Balancers on Client Access Servers

Posted on 2011-10-12
Medium Priority
Last Modified: 2012-08-13

Does anyone know what can cause NTLM authentication issues when there are multiple authentication attempts to Client Access Servers attached to a hardware load balancer or multiple load balancers? This is mostly happening when an Outlook Client is trying to connect via Outlook Anywhere (RPC over HTTP), on re-authentication attempts, the user keeps getting prompted to enter in their Active Directory credentials. This only happens when the load balancer(s) is attached to the CAS server(s) and are in an array. When the load balancer(s) are not in the picture, NTLM authentication works fine. Any help would be appreciated. Thanks.
Question by:leporej092170
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LVL 14

Expert Comment

ID: 36957869
If the load balancers are configured for ssl offloading then you would need to add the certificate to the load balancers and modify the cas accordingly. Really need more info on the load balancer configuration to assist further.

Author Comment

ID: 36958014
SSL offloading is set up as well as a certificate on the load balancers. SSL is turned off within IIS on the CAS servers. Need anymore information?

Author Comment

ID: 36968488
Anyone out there?
LVL 14

Accepted Solution

Radweld earned 1500 total points
ID: 36969199
Go to the test site,


Gotta be a problem with he load balancers really can't imagine the fault being with the cas.

Author Closing Comment

ID: 36985972
Thanks for the assistance.

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