In computer networking, peering is a voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the users of each network. The pure definition of peering is settlement-free, "bill-and-keep," or "sender keeps all," meaning that neither party pays the other in association with the exchange of traffic; instead, each derives and retains revenue from its own customers.An agreement by two or more networks to peer is instantiated by a physical interconnection of the networks, an exchange of routing information through the Border Gateway Protocol (BGP) routing protocol and, in one case out of every two hundred agreements, a formalized contractual document.Occasionally the word “peering” is used to describe situations where there is some settlement involved. In the face of such ambiguity, the phrase "settlement-free peering" is sometimes used to explicitly denote pure cost-free peering.