This article discusses a new rule for Microsoft Lync Server 2010, Best Practices Analyzer to verify IP requirements on Mediation Server.
Assume that you have a Microsoft Lync Server 2010 environment in which the Mediation Server has two network interfaces that are connected to the same subnet. In this situation, users may encounter an issue in which calls through this Mediation Server are disconnected immediately after they are connected.
To make sure that a Mediation Server that has two network interfaces is configured correctly, apply the following update, and then use Lync Server 2010, Best Practices Analyzer to scan the environment:
2672346 Description of the cumulative update for Lync Server 2010, Best Practices Analyzer: February 2013
If the IP addresses of the two network interfaces on the Mediation Server are different, but are in the same subnet, you receive the following alert title and alert text: Alert title
Calls via LYNC Mediation Server may disconnect immediately after connect
LYNC Mediation Server may have 2 network interfaces for gateway side (external) and proxy side (Internal LYNC FE). These 2 network interfaces currently have 2 unique IP addresses but they are from the same subnet in your environment. In order to have a working network routing in place, the 2 network interfaces needs to be from 2 different subnets. Both network interfaces will have their own default gateway as well. In scenarios where the gateway devices and LYNC FE are all internal and in the same network subnet, it is OK to use just 1 listening network interface for the LYNC Mediation server.