Routing Policies and Firewall Filters
4. Routing policy flow
In Junos, a routing policy flow refers to the process by which routing information is processed and evaluated by the routing policy.
1. Match: The routing policy evaluates the incoming routes against the match conditions specified in the policy.
2. Action: If the match conditions are met, the routing policy takes the specified actions on the routes, such as accepting, modifying, or rejecting the routes.
3. Next policy: If the match conditions are not met, the routing policy continues to evaluate the next policy in the policy chain. If there are no more policies in the chain, the routing information is discarded.
The routing policy flow continues until all policies in the policy chain have been evaluated or until a terminating action, such as accepting or rejecting the route, is taken. The routing policy flow allows you to specify the conditions under which routes are imported or exported and what actions are taken on the routes if the conditions are met.
5. Effect of policies on routes and routing tables
In Junos, policies have a significant effect on routes and routing tables. The policies determine which routes are accepted into the routing table, which routes are discarded, and how the routes are modified.
1. Accepting routes: Policies can be used to accept routes into the routing table based on specific conditions, such as the route's origin, AS number, or address prefix.
2. Discarding routes: Policies can be used to discard routes based on specific conditions, such as the route's origin, AS number, or address prefix.
3. Modifying routes: Policies can be used to modify routes before they are accepted into the routing table. Modifications can include changing the next hop, the preference, or the route's attributes.