Load balancer marks Client Access server as down in an Exchange Server 2013 Cumulative Update 6 environment

Original KB number:   3002351


Assume that hardware load balancing is configured to monitor Exchange Server 2013 through the default website (such as https://CAS.server_example.com). You install Cumulative Update 6 for Exchange Server 2013 on the Client Access server. In this situation, the load balancer marks the server as down, and then it stops sending requests to the server.

Additionally, an HTTP proxy log entry that resembles the following is logged on the Client Access server:

date time s-ip cs-method cs-uri-stem cs-uri-query s-port cs-username c-ip cs(User-Agent) cs(Referer) sc-status
sc-substatus sc-win32-status time-taken
2014-07-13 00:00:01 GET / Owa301RedirectUri= 443 -
- - 301 0 0 15
2014-07-13 00:00:04 GET / Owa301RedirectUri= 443 -
- - 301 0 0 0
2014-07-13 00:00:06 GET / Owa301RedirectUri= 443 -
- - 301 0 0 0


This issue occurs because of a design change in Cumulative Update 6. If you try to access the default website of the Client Access server, the server that is running Exchange Server returns status 302, and then redirects you to the Outlook Web App (OWA) website.


To resolve this issue, configure the monitor to use a website that resembles https://CAS/protocol/healthcheck.htm.

For example, you can use the following website to monitor OWA on the Client Access server:


Microsoft regularly releases software updates to address specific problems. If Microsoft releases a software update to resolve this problem, this article will be updated with additional information.