All routing protocols store their routing information in a common routing table that is maintained by JUNOS software. From the collected routing information, the JUNOS software calculates the best routes to each destination. These routes are used to forward traffic through the router, and they can be advertised to neighbors via one or more routing protocols.
Routing policy allows you to control the routing information that is transferred between different routing databases. You can filter the routing information so that only some of it is transferred, and you can set properties associated with the routes.
This chapter discusses the following topics related to understanding and configuring routing policy:
The JUNOS routing policy is quite versatile and liberal in what it allows you to configure. You can create a wide variety of policies and apply them when routes are moving between the routing protocols and the routing table. But versatility is a two-way street: the JUNOS routing policy also allows you to define nonsensical policies and to apply them so that they have unintended effects. Therefore, it is essential that you design and apply routing policies carefully.
Before designing routing policies, we recommend that you read through this entire section to become familiar with all the routing policy terminology, concepts, and configuration guidelines.
After you have designed routing policies, you should analyze them logically to ensure that they make sense. Before implementing policies, especially complex ones, you should test them to determine whether they will have the desired effect. To do this, use the test policy command.