The Local Peer Discovery protocol is an extension to the BitTorrent file-distribution system. It is designed to support the discovery of local BitTorrent peers, aiming to minimize the traffic through the Internet service provider's (ISP) channel and maximize use of higher-bandwidth local area network (LAN).
Local Peer Discovery is implemented with HTTP-like messages on User Datagram Protocol (UDP) multicast group 18.104.22.168:6771 which is an administratively scoped multicast address. While it is implemented in several clients (µTorrent, BitTorrent/Mainline, MonoTorrent, libtorrent and its derivatives, Transmission 2.0 ) and implementation is very simple, no formal specification had been created as of December, 2009. Alternative multicast protocol extension is published as BEP 26.