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Understanding How a Routing Policy Chain Is Evaluated

 

Figure 1 shows how a chain of routing policies is evaluated. These routing policies consist of multiple terms. Each term consists of match conditions and actions to apply to matching routes. Each route is evaluated against the policies as follows:

Note

On Junos OS Evolved, next term cannot appear as the last term of the action. A filter term where next term is specified as an action but without any match conditions configured is not supported.

  1. The route is evaluated against the first term in the first routing policy. If it matches, the specified action is taken. If the action is to accept or reject the route, that action is taken and the evaluation of the route ends. If the next term action is specified, if no action is specified, or if the route does not match, the evaluation continues as described in Step 2. If the next policy action is specified, any accept or reject action specified in this term is skipped, all remaining terms in this policy are skipped, all other actions are taken, and the evaluation continues as described in Step 3.

  2. The route is evaluated against the second term in the first routing policy. If it matches, the specified action is taken. If the action is to accept or reject the route, that action is taken and the evaluation of the route ends. If the next term action is specified, if no action is specified, or if the route does not match, the evaluation continues in a similar manner against the last term in the first routing policy. If the next policy action is specified, any accept or reject action specified in this term is skipped, all remaining terms in this policy are skipped, all other actions are taken, and the evaluation continues as described in Step 3.

  3. If the route does not match a term or matches a term with a next policy action in the first routing policy, it is evaluated against the first term in the second routing policy.

  4. The evaluation continues until the route matches a term with an accept or reject action defined or until there are no more routing policies to evaluate. If there are no more routing policies, then the accept or reject action specified by the default policy is taken.

Figure 1: Routing Policy Chain Evaluation
Routing Policy Chain Evaluation