peer 2 peer network programming

Hello, i try to write a peer 2 peer communication under linux with
c/c++. Unfortunately google was no big help. I found a lot about
server/client programming but nothing about peer2peer.

I already wrote a server / client appication where server and client
have been different programms. The communication takes place with
sockets. The server has one listening and one working socket. The
client one for connection.

As i understand it, a peer is simple a program which is client and
server in one. Is this true?

Do i have to fork in the beginning to get 2 processes: 1 client, 1
server?

Can i have only two clients which are communicating between each other
without a server?

Does anyone now a good source to get more information about peer2peer
network programming?

Thank you very much.