In peer-to-peer networks, like Gnutella, an overlay network is used where nodes connect to each other. Not all nodes in a network support the overlay network, so a joining node has to have a way to find nodes already in the network. Finding good nodes and connecting to them is called bootstrapping and is a problem in modern peer-to-peer networks.
Thus far, advertising nodes which are already connected to the Gnutella network was done out of band, for example using HTTP. These methods have major problems with scalability and reliability. This paper proposes a solution called UDP host caches, which makes use of the Gnutella protocol itself.
Bootstrapping Gnutella Using UDP Host Caches (PDF, 100KB)