The SAVE protocol operates alongside any routing protocol by having the
router (or set of routers) in charge of a given source address space send SAVE
updates corresponding to each forwarding table entry. Each SAVE update travels
through the network along the same path as normal traffic from that source
address space. When a downstream router receives the update, it records the
incoming interface of the update as the valid incoming direction for the corresponding
source address space. Updates are sent both periodically and whenever
a router changes its forwarding table.