How a Routing Policy Is Evaluated

You typically define match conditions and actions within a term. Figure 1 shows the routing policy components, including the term.

Figure 1: Routing Policy Components

• If a policy does not specify a match condition, all routes evaluated against the policy match.
• If a match occurs but the policy does not specify an accept, reject, next term, or next policy action, one of the following occurs:
  • The next term, if present, is evaluated.
  • If no other terms are present, the next policy is evaluated.
  • If no other policies are present, the action specified by the default policy is taken.
• If a match does not occur with a term in a policy and subsequent terms in the same policy exist, the next term is evaluated.
• If a match does not occur with any terms in a policy and subsequent policies exist, the next policy is evaluated.
• If a match does not occur by the end of a policy or all policies, the accept or reject action specified by the default policy is taken.

Figure 2 shows how a single routing policy is evaluated. This routing policy consists of multiple terms. Each term consists of match conditions and actions to apply to matching routes. Each route is evaluated against the policy as follows:

1. The route is evaluated against the first term. 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. 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. 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 matches no terms in the routing policy or the next policy action is specified, the accept or reject action specified by the default policy is taken.

Figure 2: Routing Policy Evaluation