Cisco Systems 3750E manual Icmp Router Discovery Protocol Irdp, 38-13

Chapter 38 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:
	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.

Use the no ip default-gatewayglobal 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) 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
	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.
		Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02			38-13