Internet Router Discovery (IRD) protocol
The IRD protocol is an extension of the ICMP that
is not a true routing protocol.
It uses ICMP broadcast or multicast messages to
enable hosts attached to multicast or
broadcast networks to discover the IP addresses of
their neighboring routers.
It is best used in a small network within an autonomous system.
It provides a low overhead method for routers to advertise themselves
as default routers.
It also provides a low overhead method for nonrouters to solicit
the local network for existence of routers and add to their list of
default routers the addresses of any routers that respond.
The following distinguishing features are provided by the IRD protocol: