Prefix Lists Overview

A prefix list is just like an access list: the router tests addresses one by one against the conditions in a prefix list. The first match determines whether the router accepts or rejects the address. Because the router stops testing conditions after the first match, the order of the conditions is critical. If no conditions match, the router rejects the address. An empty prefix list results in an automatic permit of the tested address.

Unlike access lists, the prefix list specifies a base IP or IPv6 address and a length (the number of bits applied to the base to determine the network prefix). The tested address is matched against the prefix.

Use the ip prefix-list command to define an IP prefix list, or the ipv6 prefix-list command to define an IPv6 prefix list. The prefix-list keyword with either the match { ip | ipv6 } address or match { ip | ipv6 } next-hop command enables you to add a clause to a route map.

Related Documentation