Category: IP Prefix Lists

IP Prefix Lists

IP Prefix lists provide mechanisms for matching two components of an IP route:

  • the route prefix
  • the prefix length

Redistribute commands cannot directly reference prefix lists, however route-maps can be referenced in redistribution, and route-maps can also reference IP Prefix lists for matching.

Prefix Lists contains one or more statements with the same name, a sequence number, and a permit or deny action.  Here is the syntax used for prefix lists:

ip prefix-list list-name [ seq seq-value ] { deny network / length | permit network / length }[ ge ge-value ] [ le le-value ]

Prefix list logic can be summarized in to a two step comparison for each route:

  1. The route’s prefix must be within the range of addresses implied by the prefix-list command’s network/length parameter
  2. The route’s prefix length must match the range of prefixes implied by the prefix-list command.