To force a diskless client or network client to select a dynamic routing protocol, its /etc/defaultrouter file should be empty. The type of dynamic routing used is selected according to the following criteria:
If the /usr/sbin/in.rdisc program exists, the startup script starts in.rdisc. Any router on the network that is running RDISC then responds to any RDISC queries from the host. If at least one router responds, the host selects RDISC as its routing protocol.
If the network router is not running RDISC or fails to respond to the RDISC queries, then in.rdisc on the host exits. The host then starts in.routed, which runs RIP.