IDRP uses Router-Advertisement and Router-Solicitation messages to discover the addresses of
routers on directly attached subnets. Each router periodically multicasts Router-Advertisement messages from each of its interfaces. Hosts then discover addresses of routers on directly attached
subnets by listening for these messages. Hosts can use Router-Solicitation messages to request
immediate advertisements rather than waiting for unsolicited messages.
IRDP offers several advantages over other methods of discovering addresses of neighboring routers.
Primarily, it does not require hosts to recognize routing protocols, nor does it require manual
configuration by an administrator.
Router-Advertisement messages enable hosts to discover the existence of neighboring routers, but
not which router is best to reach a particular destination. If a host uses a poor first-hop router to reach
a particular destination, it receives a Redirect message identifying a better choice.
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