Finding other PCs that are running the same application

[Steve_Block]

I'm writing an application that can have other instances run on other PCs and would like to setup some type of service so the applications known which other PCs are running instances of the application. Is there a way using TCP, UDP or a similar protocol in a peer to peer fashion to do this?

[Steve_Block]

It appears that UDP multicast almost does what it wants, but the machines are not always guaranteed to be in the same class D subnet. Is there a way to expand the subnet or choose a specific one?

[lagelian]

Multicast allows you to cross subnets by specifying a time to live (TTL)

http://www.tldp.org/HOWTO/Multicast-HOWTO-2.html