udp help plz

I would like to find a source code about a program that every client
is a server as well and when starts, multi casts (UDP) a hello saying
who he is.Whoever listens inside his network responds with saying its
ip and all of his neighbors in its network.So in the end everyone has
stored his neighbors and the way to send to all inside its network
anything it wants.I know its a classic, but does anyone know where to
find it, because i have some problems while trying to buid it.thanx