Changing IP for Companion Computer

See here: Alternative QGC IP Addresses?

It is recommended to change things using the user interface, not by editing files by hand.

It’s broadcast udp, it means it goes to every ip address on 192.168.2 subnet. 255 is the right number here. If you do not want broadcast you can use udpin or udpout. In mavproxy console you can enter output list to see the active outputs.