Enabling OSPF IP FRR

Procedure

1. Run system-view

   The system view is displayed.

2. Run ospf [ process-id | router-id router-id | vpn-instance vpn-instance-name ] ^*

   An OSPF process is started, and the OSPF view is displayed.

3. Run frr

   The OSPF IP FRR view is displayed.

4. Run loop-free-alternate

   OSPF IP FRR is enabled to generate a loop-free backup link.

   By default, this function is disabled. OSPF can generate a loop-free backup link only when the OSPF IP FRR traffic protection inequality is met.

   

   In the following description, Distance_opt(X, Y) indicates the shortest link from node X to node Y, S stands for a source node, E for the faulty node, N for a node along a backup link, and D for a destination node.

   • Link protection takes effect when the traffic to be protected flows along a specified link and the link cost meets the inequality: Distance_opt(N, D) < Distance_opt(N, S) + Distance_opt(S, D).

   • Node-and-link protection takes effect when the traffic to be protected flows along a specified link and passes through a specified node and the following conditions are met:

     • The link cost meets the inequality: Distance_opt(N, D) < Distance_opt(N, S) + Distance_opt(S, D).
     • The interface cost meets the inequality: Distance_opt(N, D) < Distance_opt(N, E) + Distance_opt(E, D).

5. (Optional) Run frr-priority static low

   The Loop-Free Alternates (LFA) algorithm is configured for calculating the next hop and outbound interface for a backup link.

   The next hop and outbound interface of an OSPF loop-free backup link can be obtained using either of the following methods:

   • Static backup link: After OSPF IP FRR is enabled using the ip frr command in the system view or VPN instance view, specify a next hop and an outbound interface for the static backup link.
   • Dynamic backup link: After OSPF IP FRR is enabled using the loop-free-alternate command, configure the device to use the LFA algorithm to calculate the next hop and outbound interface for the dynamic backup link.

   By default, static backup links take preference over dynamic backup links during route selection. However, static backup links are less flexible than dynamic backup links. If a link failure occurs, static backup links cannot update automatically, but dynamic backup links can. Therefore, run the frr-priority static low command to specify the LFA algorithm for calculating the next hop and outbound interface so that the dynamic backup links can take preference over static backup links.

6. (Optional) Run frr-policy route route-policy route-policy-name

   An OSPF IP FRR filtering policy is configured.

   After an OSPF IP FRR filtering policy is configured, only the OSPF backup routes that pass the filtering criteria can be delivered to the forwarding table. To protect the traffic over a specific OSPF route, you can configure a filtering policy that matches the OSPF route to ensure that the route can be added to the forwarding table. If this route fails, OSPF can fast switch the traffic to a backup route.