An MN forwarding a packet should gather all the useful routing information that it can from that packet. This subsection lists the various circumstances where routing information is added.
Route Replies: When an MN is forwarding a route reply to the MN requesting the route, it can add all the links from the requesting MN to the IN and from the MN to the destination to which a route was asked for.
Route Errors: When an MN is forwarding a Route Error back to the source, it removes all routes in its route cache that contain the link. It also removes the link from the link cache.
Neighbour Update Packets: Every node periodically sends an NU packet to the IN. The intermediate nodes on the way from the MN (which is sending the NU packet) to the IN can add all the nodes given in the NU packet to their link cache (as neighbours to the MN sending the NU packet).
Data Packets: Any data packet that is being source routed contains a path from its source to the destination. The intermediate nodes can add this information to their link caches.
