48 Patch Release Note
Patch 86251-08 for Software Release 2.5.1
C613-10356-00 REV I
Router Advertisement
Messages
A router advertisement is an ICMP (type 10) message containing:
■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.
Router 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.
Router Advertisement
Interval
The router advertisement interval is the time between router advertisements.
For the first few advertisements sent from an interface (up to 3), the router
sends the router advertisements at intervals of at most 16 seconds. After these
initial transmissions, it sends router advertisements at random intervals
between the minimum and maximum intervals that the user configures, to
reduce the probability of synchronization with the advertisements from other
Table 9: Router Discovery Process
When ... Then ...
Router Discovery advertising starts on a
router interface because:
- the router starts up, or
- advertisements are enabled on the switch
or on an interface
the router multicasts a router advertisement
and continues to multicast them periodically
until router advertising is disabled.
a host starts up the host may send a router solicitation
message.
the router receives a router solicitation the router multicasts an early router
advertisement on the multicast interface on
which it received the router solicitation.
a host receives a router advertisement the host stores the IP address and preference
level for the advertisement lifetime.
the lifetime of all existing router
advertisements on a host expires
the host sends a router solicitation.
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 multicasts a router advertisement
with the IP address(es) that stopped
advertising, and a lifetime of zero (0). It
continues to periodically multicast router
advertisements for other interfaces.
the router receives a router advertisement
from another router
the router does nothing but silently discards
the message.