An implementation of RIP SHOULD provide for a graceful shutdown using the following steps:
The metric used for the above really ought to be 16 (infinity); setting it to 15 is a kludge to avoid breaking certain old hosts that wiretap the RIP protocol. Such a host will (erroneously) abort a TCP connection if it tries to send a datagram on the connection while the host has no route to the destination (even if the period when the host has no route lasts only a few seconds while RIP chooses an alternate path to the destination).
Split horizon SHOULD be applied to static routes by default. An implementation SHOULD provide a way to specify, per static route, that split horizon should not be applied to this route.