Cisco Systems 3750E Caching Source-Active State, Ip prefix-list name description string, 43-6

Chapter 43 Configuring MSDP

Configuring MSDP

	Command	Purpose
Step 3
	ip prefix-list name [description string]	(Optional) Create a prefix list using the name specified in Step 2.
	seq number {permit deny} network	• (Optional) For description string, enter a description of up to 80
	length
		characters to describe this prefix list.
		• For seq number, enter the sequence number of the entry. The range
		is 1 to 4294967294.
		• The deny keyword denies access to matching conditions.
		• The permit keyword permits access to matching conditions.
		• For network length, specify the network number and length (in bits)
		of the network mask that is permitted or denied.
Step 4
	ip msdp description {peer-name	(Optional) Configure a description for the specified peer to make it
	peer-address}text	easier to identify in a configuration or in show command output.
		By default, no description is associated with an MSDP peer.
Step 5
	end	Return to privileged EXEC mode.
Step 6
	show running-config	Verify your entries.
Step 7
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To remove the default peer, use the no ip msdp default-peerip-address name global configuration command.

This example shows a partial configuration of Router A and Router C in Figure 43-2. Each of these ISPs have more than one customer (like the customer in Figure 43-2) who use default peering (no BGP or MBGP). In that case, they might have similar configurations. That is, they accept SAs only from a default peer if the SA is permitted by the corresponding prefix list.

Router A

Router(config)# ip msdp default-peer 10.1.1.1

Router(config)# ip msdp default-peer 10.1.1.1 prefix-list site-a

Router(config)# ip prefix-list site-b permit 10.0.0.0/1

Router C

Router(config)# ip msdp default-peer 10.1.1.1 prefix-list site-a

Router(config)# ip prefix-list site-b permit 10.0.0.0/1

Caching Source-Active State

By default, the switch does not cache source/group pairs from received SA messages. When the switch forwards the MSDP SA information, it does not store it in memory. Therefore, if a member joins a group soon after a SA message is received by the local RP, that member needs to wait until the next SA message to hear about the source. This delay is known as join latency.

If you want to sacrifice some memory in exchange for reducing the latency of the source information, you can configure the switch to cache SA messages.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

43-6 OL-9775-02