In the Arc10 Q&A for the 2011 user conference it says a performance gain may be realized by hardcoding the license manager to port 27000, and then instructing the firewall and Windows Defender to ignore that port.
That same doc references the online help for the specifics of how to implement that on the license manager server, namely edit
services.txt to look like the below (the trailing numbers on first two lines used to blank):
SERVER this_host ANY 27000 VENDOR ARCGIS PORT=1234 FEATURE ACT ARCGIS 1 permanent 1 7ED49106D630
This is all well and good to this point, but I'm confused about what is happening with the server port and the vendor ports. Which way does the communication flow go? If the ArcGIS Vendor port is hardcoded, then does every client need to be updated to explicitly match that port? (e.g. do I have to visit every client machine and set their ArcGIS Desktop Adminstrator to use port 1234? or is it 27000?) Do I set the firewall to ignore one port or both ports? in or out? And is #1234 actually a safe number, or range of numbers?