3Com 10014298 Defining IP Prefix, Configuring for Filtering Received Routes, Defining Prefix-list

IP Routing Policy 103

Defining IP Prefix

A prefix list is identified by the IP prefix name. Each IP prefix can include multiple items, and each item can specify the matching range of the network prefix forms. The index-numberparameter specifies the matching sequence in the prefix list.

Perform the following configurations in system view.

Table 104 Defining Prefix-list

Operation	Command
Define a prefix list	ip ip-prefixip-prefix-name [
	index index-number ] { permit
	deny } network len [
	greater-equalgreater-equal ] [
	less-equalless-equal ]
Remove a prefix list	undo ip ip-prefix ip-prefix-name
	[ index index-number permit
	deny ]

During the matching, the router checks list items identified by the index-numberin the ascending order. If only one list item meets the condition, it means that it has passed the ip-prefix filtering (and does not enter the testing of the next list item).

If more than one IP prefix item is defined, then the match mode of at least one list item should be the permit mode. The list items of the deny mode can be defined to rapidly filter the routing information not satisfying the requirement, but if all the items are in the deny mode, no route will pass the ip-prefix filtering. You can define an item of permit 0.0.0.0/0 greater-equal 0 less-equal 32 after the multiple list items in the deny mode to let all the other routes pass.

Configuring for Filtering Received Routes

Perform the following configuration in routing protocol view.

Define a policy that filters the routing information that does not satisfy the conditions and receives routes with the help of an ACL or address prefix-list. The filter-policy gateway command specifies that only the update packets from a specific neighboring router will be received.

Table 105 Configuring Filtering for Received Routes

Operation	Command
Configure to filter the received routing	filter-policy gateway
information distributed by the specified	ip-prefix-name import
address
Cancel the filtering of the received routing	undo filter-policy gateway
information distributed by the specified	ip-prefix-name import
address

Configure to filter the received global routing information

Cancel the filtering of the received global routing information

filter-policy{ acl-number ip-prefixip-prefix-name } [ gateway ] import

undo filter-policy { acl-number ip-prefix ip-prefix-name } [ gateway ] import