Allied Telesis X8100, x908 manual One or more prefixes, by using a prefix list

BGP: Configuring Route Maps

Expanded lists use regular expressions to specify the communities. They can be identified by a number, or by the word expanded, and are created by using any of the following commands:

awplus(config)# ip community-list <100-199>{denypermit} <reg-exp>

awplus(config)# ip community-list expanded <list-name> {denypermit} <reg-exp>

You can have multiple entries in a community list. Entries are unnumbered, so each new entry gets added at the end of the list.

There is an implicit exclude all else entry at the end of the community list.

Applying Once you have created a community list, use it in a route map entry by using the command:

awplus(config-route-map)#match community <list> [exact-match]

The optional exact-match parameter specifies that the communities contained in the attribute section of the update message must exactly match the specified community list. If you do not specify exact-match, then the set of communities in the attribute list of the update message must include all the communities in the specified community list, but can also include other communities.

One or more prefixes, by using a prefix list

For information about creating a prefix list, see "About prefix lists" on page 22.

Once you have made the prefix list, apply it to the match clause of a route map entry by using the command:

awplus(config-route-map)#match ip address prefix-list <list-name>

A prefix list can match a subset of prefixes in an update message. You can use this to change the attributes of some of the prefixes in an outgoing update, without having to change the attributes of all the prefixes. However, an update message contains just one set of attributes, which must apply to all the prefixes in the update.

If a route map entry matches on some of the prefixes in a particular outgoing update message, and has an associated set clause that specifies a change to the attributes for those prefixes, then the switch splits the update into two update packets:

one that contains the original attribute values and the prefixes that were not included by the route map entry, and

one that contains the new attribute values and the prefixes that were included by the route map entry.

One or more prefixes, by using an ACL

An ACL is an alternative to a prefix list for matching a prefix in an update message.

For information about creating an ACL, see "About ACLs" on page 11.

Use Route Maps and Other Filters to Filter and Alter BGP and OSPF Routes Page 29