Configuring OSPF to Filter the Received Routes

Procedure

1. Run system-view

   The system view is displayed.

2. Run ospf [ process-id ]

   The OSPF view is displayed.

3. Set the conditions to filter the received routes.

   Run any of the following commands as required:

   • Based on the basic ACL:

     1. Run quit

        Return to the system view.

     2. Run acl { name basic-acl-name { basic | [ basic ] number basic-acl-number } | [ number ] basic-acl-number } [ match-order { config | auto } ]

        The ACL view is displayed.

     3. Run rule [ rule-id ] [ name rule-name ] { deny | permit }

        A rule is configured for the ACL.

        When the rule command is used to configure a filtering rule for a named ACL, only the configurations specified by source and time-range take effect.

        When a filter-policy of a routing protocol is used to filter routes:

        • If the action specified in an ACL rule is permit, a route matching the rule will be accepted or advertised by the system.

        • If the action specified in an ACL rule is deny, a route matching the rule will not be accepted or advertised by the system.

        • If the network segment of a route is not within the range specified in an ACL rule, the route will not be accepted or advertised by the system.

        • If an ACL does not contain any rules, none of the routes matched against the filter-policy that uses this ACL will be accepted or advertised by the system.

        • Routes can be filtered using a blacklist or whitelist:

          If ACL rules are used for matching in configuration order, the system matches the rules in ascending order of their IDs.

          Filtering using a blacklist: Configure a rule with a smaller ID and specify the action deny in this rule to filter out the unwanted routes. Then, configure another rule with a larger ID in the same ACL and specify the action permit in this rule to accept or advertise the other routes.

          Filtering using a whitelist: Configure a rule with a smaller ID and specify the action permit in this rule to permit the routes to be accepted or advertised. Then, configure another rule with a larger ID in the same ACL and specify the action deny in this rule to filter out the unwanted routes.

     4. Run ospf [ process-id ]

        The OSPF view is displayed.

     5. Run filter-policy { acl-number | acl-name acl-name } import

        An import policy that is based on the basic ACL is configured to filter routes received by OSPF.

   • Based on the IP prefix list:

     Run filter-policy ip-prefix ip-prefix-name import

     An import policy that is based on the IP prefix list is configured to filter routes received by OSPF.

4. Run commit

   The configuration is committed.