Cisco Systems 3750E manual Ip pim send-rp-discovery scope ttl, Show ip pim rp mapping, 42-18

Chapter 42 Configuring IP Multicast Routing

Configuring IP Multicast Routing

	Command	Purpose
Step 5
	ip pim send-rp-discovery scope ttl	Find a switch whose connectivity is not likely to be interrupted, and
		assign it the role of RP-mapping agent.
		For scope ttl, specify the time-to-live value in hops to limit the RP
		discovery packets. All devices within the hop count from the source
		device receive the Auto-RP discovery messages. These messages tell
		other devices which group-to-RP mapping to use to avoid conflicts (such
		as overlapping group-to-RP ranges). There is no default setting. The
		range is 1 to 255.
Step 6
	end	Return to privileged EXEC mode.
Step 7
	show running-config	Verify your entries.
	show ip pim rp mapping	Display active RPs that are cached with associated multicast routing
	show ip pim rp	entries.
		Display the information cached in the routing table.
Step 8
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To remove the PIM device configured as the candidate RP, use the no ip pim send-rp-announceinterface-idglobal configuration command. To remove the switch as the RP-mapping agent, use the no ip pim send-rp-discoveryglobal configuration command.

This example shows how to send RP announcements out all PIM-enabled interfaces for a maximum of 31 hops. The IP address of port 1 is the RP. Access list 5 describes the group for which this switch serves as RP:

Switch(config)# ip pim send-rp-announce gigabitethernet1/0/1 scope 31 group-list 5

Switch(config)# access-list 5 permit 224.0.0.0 15.255.255.255

Preventing Join Messages to False RPs

Find whether the ip pim accept-rpcommand was previously configured throughout the network by using the show running-configprivileged EXEC command. If the ip pim accept-rpcommand is not configured on any device, this problem can be addressed later. In those routers or multilayer switches already configured with the ip pim accept-rpcommand, you must enter the command again to accept the newly advertised RP.

To accept all RPs advertised with Auto-RP and reject all other RPs by default, use the ip pim accept-rpauto-rpglobal configuration command. This procedure is optional.

If all interfaces are in sparse mode, use a default-configured RP to support the two well-known groups 224.0.1.39 and 224.0.1.40. Auto-RP uses these two well-known groups to collect and distribute RP-mapping information. When this is the case and the ip pim accept-rpauto-rpcommand is configured, another ip pim accept-rpcommand accepting the RP must be configured as follows:

Switch(config)# ip pim accept-rp 172.10.20.1 1

Switch(config)# access-list 1 permit 224.0.1.39

Switch(config)# access-list 1 permit 224.0.1.40

Filtering Incoming RP Announcement Messages

You can add configuration commands to the mapping agents to prevent a maliciously configured router from masquerading as a candidate RP and causing problems.

Beginning in privileged EXEC mode, follow these steps to filter incoming RP announcement messages. This procedure is optional.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
42-18	OL-9775-02