
IP Concepts, Terminology, and Features
117356-A Rev. A 1-11
Routers establish EGP neighbor relationships in order to periodically exchange
reliable network reachability information. The router uses this information to
maintain a list of gateways, the networks the gateways can reach, and the
corresponding distances.
Router Discovery Protocol
Before a host can send IP datagrams beyond its directly attached subnet, the host
must discover the address of at least one operational router on that subnet. Router
Discovery is an extension of the Internet Control Message Protocol (ICMP) that
enables hosts attached to multicast or broadcast networks to discover the IP
addresses of their neighboring routers.
Routers configured with Router Discovery periodically multicast or broadcast a
router advertisement from each of their interfaces, announcing the IP address or
addresses of that interface. Hosts discover the addresses of their neighboring
routers by listening for these advertisements. Hosts will use the router with the
highest preference level as a gateway.
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