JUNOS Cookbook

Chapter 9. Routing Policy and Firewall Filters

Introduction

The JUNOS software policy framework provides a mechanism for controlling the flow of traffic into and out of the router. The policy framework has two broad components:

Routing policy

Controls routing information that routing protocols place into the routing and forwarding tables and advertise based on the routes in the routing table.

Firewall filters

Control packets passing through a router’s interface, either coming into the router or being transmitted out.

The architectural design and configuration of JUNOS routing policy and firewall filters and how you configure them are nearly identical, so we discuss them together in a single chapter. However, because they are so similar, it’s sometimes easy to confuse the two. The most important point to remember is that routing policy applies to routing protocols and affects how routes are stored in the routing table and how routes are advertised to peers, while firewall filters affect which packets a router’s interfaces accept and send.

The process for configuring policies and filters always has two basic steps:

1. Define the policy or filtering conditions in one part of the configuration ([edit policy-options] for routing policies and [edit firewall] for firewall filters).

2. Apply the conditions by referencing them when configuring either a specific routing protocol or a specific interface.

Separating the specification of policy and firewall conditions from their actual application means ...