[This is preliminary documentation and subject to change.]
A change in any of the following values for the best route to a given destination network, causes the RTM to generate a notification message that is sent to each registered client and to the forwarders.
A change in protocol identifier, interface index, or next-hop router address can occur when a new, better-route entry is added, or when the current best-route entry is deleted or aged out, leaving another route as the new best route.