Specifications

ICMP Router Discovery Advertisements (CR00010614) 159
Version 291-18
C613-10488-00 REV Q
Advertisement messages
A router advertisement is an ICMP (type 10) message that contains the following:
■ in the destination address field of the IP header, the interface's configured advertisement address, either 224.0.0.1 (all) or 255.255.255.255 (limited).
■ in the lifetime field, the interface's configured advertisement lifetime.
■ in the Router Address and Preference Level fields, the addresses and preference levels of all the logical interfaces that are set to advertise.
The router or switch does not send router advertisements by default.
Solicitation messages
A router solicitation is an ICMP (type 10) message containing:
■ source Address: an IP address belonging to the interface from which the message is sent
■ destination Address: the configured Solicitation Address, and
■ Time-to-Live: 1 if the Destination Address is an IP multicast address; at least 1 otherwise.
a host does not receive a router
advertisement after sending a small number
of router solicitations
the host waits for the next unsolicited router
advertisement
a host needs a default router address the host uses the IP address of the router or
L3 switch with the highest preference level.
Router Discovery advertising is deleted from
the physical interface (delete ip advertise
command), or the logical interface has
advertise set to no (set ip interface
command)
the router or switch multicasts a router
advertisement with the IP address(es) that
stopped advertising, and a lifetime of zero. It
continues to periodically multicast router
advertisements for other interfaces.
the router or switch receives a router
advertisement from another router
the router or switch does nothing but silently
discards the message.
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