1) Start MW3 Dedi Server from Steam Tools
2) Type in the name of your Dedicated Server Playlist (.DSPL) for dvar “sv_mapRotation”
3) Do a start_map_rotate command to run your server
If you get “Invalid server configuration – strict NAT detected.”, you may need to open ports and/or make exceptions for your AntiVirus.
To fix the Master servers not being found, copy Steam.dll from your Steam directory to the dedicated server root directory and restart the server.