Routing Policies and Firewall Filters

For example, you can use a policy to match routes based on the AS number and then set a specific next hop for the matching routes. This allows you to control the flow of routing information and ensure that the routing table contains the most accurate and up-to-date information. By specifying match criteria, match types, and actions, policies give you a high degree of control over the routing information in your network.

Example of a Junos routing policy with explanation:

policy-options {
    policy-statement prefer-local-routes {
        term prefer-local-routes {
            from {
                route-filter 192.168.1.0/24 exact;
            }
            then {
                preference 100;
                accept;
            }
        }
        term reject-all {
            then reject;
        }
    }
}

This routing policy, named prefer-local-routes, has two terms: prefer-local-routes and reject-all.

The prefer-local-routes term matches routes with a destination of 192.168.1.0/24. If a route matches this term, it is assigned a preference value of 100 and is accepted into the routing table. A higher preference value means that a route is preferred over other routes with lower preference values.

The reject-all term matches all remaining routes and rejects them. This term ensures that any routes that don't match the prefer-local-routes term are not added to the routing table.

When a Junos device receives routing updates, it evaluates each update against the terms in this policy. If a route matches the prefer-local-routes term, it is accepted and added to the routing table with a preference value of 100. If a route does not match this term, it is rejected and not added to the routing table.

This policy ensures that local routes with a destination of 192.168.1.0/24 are preferred over other routes, and that all other routes are rejected.

Routing Policies and Firewall Filters

6. Policy structure and terms

7. Policy match criteria, match types, and actions