Configuring IRDP
Fixed Switch Configuration Guide 21-5
Configuring IRDP
Using IRDP in Your Network
The ICMP Router Discovery Protocol (IRDP), described in RFC 1256, enables a host on multicast
or broadcast networks to determine the address of a router it can use as a default gateway. Routing
interfaces that are enabled for IRDP periodically send out ICMP Router Advertisement messages
announcing the IP address of that interface. Hosts on the link discover the addresses of their
neighboring routers by listening for advertisements. Hosts on startup also may send out ICMP
Router Solicitation messages to ask for immediate advertisements.
IRDP is disabled by default on fixed switch platforms.
IRDP Configuration Overview
When you configure a routing VLAN interface to participate in IRDP, the only required step is to
enable IRDP on the interface. You can keep the default values defined for the IRDP parameters, or
change them:
• Maximum and minimum advertisement intervals — set the maximum and minimum
intervals in seconds between IRDP advertisements sent by the routing interface. The default
values set the advertising rate to once every 7 to 10 minutes.
• Advertisement lifetime or holdtime — sets the maximum length of time in seconds that the IP
address sent in the IRDP advertisement should be considered valid.
• Router preference level — sets the preference level for the advertised router address. Hosts
use this value when choosing a default router address, choosing the router address with the
highest preference. You can use this value to encourage or discourage use of a particular
router as a default router.
• Advertisement address — sets the IP destination address used in the advertisements sent by
the interface. The only permissible values are the all-systems multicast address, 224.0.0.0.1, or
the limited-broadcast address, 255.255.255.255.
IRDP Configuration Example
Table 21-3 lists the default IRDP configuration values.
Procedure 21-2 on page 21-6 lists the basic steps to configure IRDP and the commands used.
Table 21-3 IRDP Default Values
Parameter Description Default Value
IRDP process The IRDP router process on the routing
interfaces.
disabled on all interfaces
maximum advertisement
interval
The maximum time allowed between
sending multicast router advertisements
from the interface.
Can range between 4 and 1800 seconds.
600 seconds
minimum advertisement
interval
The minimum time allowed between
sending multicast router advertisements
from the interface.
Can be no less than 3 seconds.
three-fourths of the maximum
advertisement interval.
(450 seconds)
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