Ubuntu Networking :: Member Of All Groups Communicate Simultaneously With ALL Computers?

given my computer is in a network consisting of multiple subnetworks, i.e. there are groups of computers: {192.168.1.1, 192.168.1.2, 192.168.1.3 etc.}, {192.168.2.1, 192.168.2.2, 192.168.2.3 etc.},..., {192.168.254.1, 192.168.254.2, 192.168.254.3 etc.}. My computer is 192.168.1.1. So I can communicate with 192.168.1.2, 192.168.1.3 etc. To communicate with other people I have manually switch to the proper subnetwork and take a new ip, e.g. 192.168.2.1. My question is: Is there any way to be member of all groups and communicate simultaneously with ALL computers? And if not, is there a way to find out (without manually changing the ip address) if computers of other subnetworks are online, so one does not have to change the ip and then look for other computers in the new subnetwork?