Junos : Routing Policy

Overview

A routing policy is the method that you can use to control what routes from dynamic routing policies (OSPF, BGP, RIP, etc) get imported into your routing table and or advertised to other peers or neighbors.

Import Policy

The import policy is responsible for changing or modifying any routes that are advertised to you by other neighbors or peers. Import policies are most commonly seen changing route metrics or preferences or filtering certain routes from being put into your routing table. The Import policy effects how your router views the world.

Export Policy

The export policy is responsible for filtering or modifying routes that you are adverting to other peers or neighbors. Export policies are most commonly seen changing metrics or preferences of routes or re advertising routes from other routing protocols into the protocol that has the export policy tied to it.

Default Routing Policies

Each routing protocol has a default routing policy associated with it that is not specifically defined in the configuration and each one is different.

RIP

By default (without a routing policy) a JunOS device will accept all RIP routes advertised to it by its explicitly configured neighbors but will not advertise those routes at all.

OSPF

Just like RIP, by default (without a routing policy) a JunOS device will accept all OSPF LSA's and exports all routes learned by OSPF but no other protocols. Link State Protocols depend on all routers having the exact same picture of the network so import and export policies on OSPF are pretty limited.

BGP

By default (without a routing policy) a JunOS device will import and export all BGP routes to and from the routing table.