Category: Route Maps

Route Maps

Route Maps are similar to If/Then/Else logic seen in other programming languages.  a route map contains route-map commands, and routers process route-map commands in sequential order based on sequence number.

Each route-map command has matching parameters, and also one or more optional set commands that you can use to manipulate what you’ve matched.  Here are the rules route-maps have to abide by:

  • each route-map must have a configured name, with all commands using the same name being part of the same route-map
  • Each route-map has a permit or deny action
  • each route-map command has a sequence number, you can delete and route-map commands by inserting them into the existing sequence.
  • when route-maps are used for distribution they process routes from the current routing table.
  • route-maps are processed sequentially based on sequence numbers
  • once a route has been matched by a route map it is not checked by any subsequent route map commands
  • when a route is matched in a statement, if the command is a permit action the route will be redistributed (specific to redistribution)
  • when a route is matched in a statement, if the command is a deny action the route is not distributed (specific to redistribution)

Route map logic when used for redistribution:

  • route-map commands with the permit option either cause a route to be redistributed or leave the route in the list of routes  to be examined by the next route-map clause
  • route-map commands with the deny option will either filter the route or leave the route in the list of routes to be examined by the next route-map command
  • If a clause’s match commands use an ACL, an ACL match with the deny action does not cause the route to be just means that the route does not match that specific clause
  • if the route map command includes an implied deny all clause to configure a permit all configure a route-map command with an action  to permit but no matching commands.