This is one excellent tool that will prove to be very valuable in troubleshooting scenario's.
The Lync Firewall Rules Viewer is a Windows 7 application that visually illustrates the network traffic between any pair of server or client Lync endpoints. When the administrator selects a source endpoint in the left pane, the list of possible destination endpoints this source can communicate with is shown in the right pane (See figures below).
On a 64-bit system I got the following error when opening the application:
I did exactly that but still it didn't work. I only get it working on a 32-bit system, what's your experience? I'll contact the author for more information