Alef/nocdkey – User

nocdkey here doesn't mean you can play illegal copies with this plugin!
This plugin simulate what you usually can do just dropping your connection to the internet.

This is a file called ws2_32.dll to put in the same arma.exe directory, and get enabled using -nocdkey and -host arguments on the command line. It will intercept the host name resolution for gamespy service, returning a "not found" answer. This is the same effect you can obtain disconnecting the network cable.

How to run 2 ArmAs on the same PC

Need a crafted ws2_32.dll, which returns WSAHOST_NOT_FOUND in gethostbyname() for armedass.master.gamespy.com or armedass.available.gamespy.com if -nokey is given on the server (-host) command line.

Editor/Server:
\ArmA\arma.exe -window -nosplash -world=empty -nopause -host -nokey

Client:
\ArmA\arma.exe -window -nosplash -world=empty -nopause -connect=localhost

The server will get the message "No challenge value was received from the master server."

Will post on OFPEC for beta, if someone interested, and on BI forum.