System information

Configuring Interfaces and TCP/IP Features
5-21
With IRDP, each router periodically multicasts or broadcasts router advertisement
messages from each of its interfaces. Hosts discover the addresses of routers on the
directly attached subnet by listening for these messages. Hosts can use router
solicitation messages to request immediate advertisements, rather than wait 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 allow 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.
Enabling IRDP
Use the following procedure to configure IRDP.
1. To enable IRDP, use the ip irdp command in Interface Configuration mode, as
shown below:
MOT(config-if)#ip irdp
2. To configure a proxy IP address to advertise messages from an interface, use the
ip irdp address command in Interface Configuration mode, as shown below
MOT(config-if)#ip irdp address <A.B.C.D> [address <A.B.C.D> |
holdtime <number1> | maxadvertinterval <number2> | minadvertinterval
<number3> | multicast | preference <number4>]
where:
address is the IP addresses to proxy-advertise, preference value.
A.B.C.D is the IP address of the interface on which the messages are
advertised.
holdtime is the amount of time that advertisements are valid, expressed in
seconds.
number1 is the holdtime, expressed in seconds; valid entries are 1 to 9000;
default is 1800.