Filtering Prefixes

To filter routes based on the prefix, you can do any of the following:

• Define an access list with the access-list or ipv6 access-list command, and apply the list to routes received from or passed to a neighbor with the neighbor distribute-list command.
• Define a prefix list with the ip prefix-list command, and apply the list to routes received from or passed to a neighbor with the neighbor prefix-list command.
• Define a prefix tree with the ip prefix-tree command, and apply the list to routes received from or passed to a neighbor with the neighbor prefix-tree command.

The router compares each route's prefix against the conditions in the list or tree, one-by-one. If the first match is for a permit condition, the route is accepted or passed. If the first match is for a deny condition, the route is rejected or blocked. The order of conditions is critical because testing stops with the first match. If no conditions match, the router rejects or blocks the address; that is, the last action of any list is an implicit deny condition for all routes. The implicit rule is displayed by show access-list and show config commands.

You cannot selectively place conditions in or remove conditions from an access list, prefix list, or prefix tree. You can insert a new condition only at the end of a list or tree.

Copyright © 2008, Juniper Networks, Inc. All rights reserved. Trademark Notice.