In general, all addresses in the range 127.xxx.xxx.xxx can be used for loopback. However, by design, Citect uses the most commonly-used loopback address only, which is 127.0.0.1. When using any other addresses, Citect will not recognise this IP address and you will not be able to set this computer as a server in the computer set-up wizard, and will recieve #coms when the project is run.