This section provides information on two protocols, STUN and Kademlia.
Kademlia is a DHT which uses XOR as a metric. That is, items in the DHT are represented by fixed-length binary keys, and the distance between any two items is the byte-wise exclusive OR (XOR) of their keys. Items might be either nodes or data being stored. The Kademlia protocol is specified as running over UDP, although this does not seem to be an essential part of the protocol.
STUN is a protocol used by clients behind NATs, network address translation devices, to discover information about the NATs and what the outside world sees as a client's IP address and port number.