Cisco Catalyst 3750 - ICMP Router Discovery Protocol (IRDP)

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Catalyst 3750 MetroSwitch Software Configuration Guide
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Chapter 28 Configuring IP Unicast Routing
Configuring IP Addressing
Beginning in privileged EXEC mode, follow these steps to define a default gateway (router) when IP
routing is disabled:
Use the no ip default-gateway global configuration command to disable this function.
ICMP Router Discovery Protocol (IRDP)
Router discovery allows the switch to dynamically learn about routes to other networks using IRDP.
IRDP allows hosts to locate routers. When operating as a client, the switch generates router discovery
packets. When operating as a host, the switch receives router discovery packets. The switch can also
listen to Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP) routing
updates and use this information to infer locations of routers. The switch does not actually store the
routing tables sent by routing devices; it merely keeps track of which systems are sending the data. The
advantage of using IRDP is that it allows each router to specify both a priority and the time after which
a device is assumed to be down if no further packets are received.
Each device discovered becomes a candidate for the default router, and a new highest-priority router is
selected when a higher priority router is discovered, when the current default router is declared down,
or when a TCP connection is about to time out because of excessive retransmissions.
The only required task for IRDP routing on an interface is to enable IRDP processing on that interface.
When enabled, the default parameters apply. You can optionally change any of these parameters.
Beginning in privileged EXEC mode, follow these steps to enable and configure IRDP on an interface:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
ip default-gateway ip-address Set up a default gateway (router).
Step 3
end Return to privileged EXEC mode.
Step 4
show ip redirects Display the address of the default gateway router to verify the
setting.
Step 5
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and specify the Layer 3 interface to
configure.
Step 3
ip irdp Enable IRDP processing on the interface.
Step 4
ip irdp multicast (Optional) Send IRDP advertisements to the multicast address
(224.0.0.1) instead of IP broadcasts.
Note This command allows for compatibility with Sun Microsystems
Solaris, which requires IRDP packets to be sent out as multicasts.
Many implementations cannot receive these multicasts; ensure
end-host ability before using this command.
Step 5
ip irdp holdtime seconds (Optional) Set the IRDP period for which advertisements are valid. The
default is three times the maxadvertinterval value. It must be greater
than maxadvertinterval and cannot be greater than 9000 seconds. If you
change the maxadvertinterval value, this value also changes.