The Local Peer Discovery protocol, specified as BEP-14, [1] 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 networks (LANs).
Local Peer Discovery is implemented [2] with HTTP-like messages on User Datagram Protocol (UDP) multicast group 239.192.152.143:6771 (IPv4) or ff15::efc0:988f (IPv6) [1] which are administratively scoped multicast addresses. It's similar to Simple Service Discovery Protocol but sends BT-SEARCH instead of M-SEARCH:
BT-SEARCH * HTTP/1.1\r\nHost: <host>\r\nPort: <port>\r\nInfohash: <ihash>\r\ncookie: <cookie (optional)>\r\n\r\n\r\n
Since implementation is simple, Local Peer Discovery is implemented in several clients (μTorrent, [3] BitTorrent/Mainline, [4] MonoTorrent, [5] libtorrent [6] and its derivatives, Transmission, [7] aria2 [8] ). An alternative multicast peer discovery protocol based on ZeroConf is published as BEP 26 Zeroconf Peer Advertising and Discovery, but is not widely adopted since it is considered too complex [9] in comparison.