There are many options in the LoadMaster which relate to the use of Microsoft Exchange 2010. This article describes some best practices for setting up specific Exchange Virtual Services, especially MAPI. When configuring a MAPI Virtual Service, there are two schools of thought; quick and easy or thorough and precise. Clients will connect to a Client Access Server (CAS) over port 135 until instructed to connect over a high port for a more secure connection. The idea of balancing this type of traffic can be tricky.
The first question to answer is, “Are my Remote Procedure Call (RPC) ports set statically within Exchange?”. Setting the RPC ports statically is not a required configuration to maintain Exchange connectivity, but KEMP Technologies recommends it. To set the RPC ports statically, refer to the following Technet article: Configure Static RPC Ports on an Exchange 2010 Client Access Server.
If using this type of setup, KEMP recommends moving away from a wildcard (*) service to handle these types of request and create a port 135 service. While configuring the new MAPI service, add the static ports in the Extra Ports field. Multiple ports can be added to this text box, separating each entry with a space. Once added, the LoadMaster will send health checks to the server over port 135 port as well as the other ports that you have specified. This configuration is preferred over three separate services, due to the fact that persistence records can be shared now that all of the requested ports are wrapped within one Virtual Service.
For a quicker and more simplistic setup, you can use a wildcard (*) Virtual Service. The wildcard service will listen for all requests for a given IP address that are not already accounted for by other Virtual Services sharing the same IP. This setup works quite well for Exchange as it is able to capture all of the MAPI requests within one Virtual Service. One of the downsides to this type of service is that we will respond to a request made on ANY port. Clients will be able to request any port on the Virtual Service IP and they will get a response from the LoadMaster. In turn, the LoadMaster will attempt to contact the server over this requested port. This can cause erroneous log messages within the LoadMaster due to not being able to connect clients to the server over a port that is closed.
If those options are not enough, as of Service Pack 2 - Microsoft Exchange 2010 allows RPC over HTTP(S). So, MAPI traffic can also be sent to a Virtual Service over port 443. The KEMP HTTPS template for Exchange can handle the additional traffic.