Loose source routing uses a source routing option in TCP/IP to record the set of routers a packet must visit. The destination of the packet is replaced with the next router the packet must visit. By setting the forwarding agent (FA) to one of the routers that the packet must visit, LSR is equivalent to tunneling. If the corresponding node stores the LSR options and reverses it, it is equivalent to the functionality in mobile IPv6.
The name loose source routing comes from the fact that only part of the path is set in advance. This is in contrast with strict source routing, in which every step of the route is decided in advance when the packet is sent.