Peer-to-peer architecture The concept of a server that is always on is not used here. Instead, the two haystacks (called piers) communicate directly with each other. This is called peer-to-peer architecture, since no direct hosts or servers are required for direct connectivity between two hosts. The difference with client server architecture is easily noticed. There is no need for the host to be always on. Communication needs to be turned on. And if the two hosts want to communicate with each other again, then changing their IP address will not cause any problem. Gnutella is a notable example of peer-to-peer architecture . This is an open source P2P file sharing application. Using Gnutella , any host can request for a file , search the file , respond to another host's request , and forward queries to any corner.