Configuring OSPF TI-LFA FRR

This section describes how to configure OSPF TI-LFA FRR.

Usage Scenario

For some large networks, especially for the networks where the P space and Q space neither intersect nor have directly connected neighbors, if a link or node fails, LFA and RLFA cannot compute a backup path, causing traffic loss and failing to meet reliability requirements. To resolve this issue, TI-LFA is introduced.

TI-LFA FRR provides link and node protection for SR tunnels. If a link or node fails, it enables traffic to be rapidly switched to a backup path, minimizing traffic loss.

Pre-configuration Tasks

Before configuring OSPF TI-LFA FRR, complete the following tasks:

Configure addresses for interfaces to ensure that neighboring devices are reachable at the network layer.
Configure basic OSPF functions
Enable SR globally.
Enable SR for the corresponding OSPF process.

Procedure

Run system-view
The system view is displayed.
Run ospf [ process-id ]
An OSPF process is created, and the OSPF view is displayed.
Run frr
The OSPF FRR view is displayed.
Run loop-free-alternate
OSPF LFA is enabled, and LFA links can be generated.
Run ti-lfa enable
OSPF TI-LFA is enabled.
(Optional) Run tiebreaker { node-protecting | lowest-cost | ldp-sync hold-max-cost | srlg-disjoint } preference preference
An OSPF TI-LFA FRR tiebreaker for backup path computation is configured.

A larger value indicates a higher preference.

Before configuring the srlg-disjoint parameter, you need to run the ospf srlg srlg-value command in the OSPF interface view to configure the OSPF SRLG function.
(Optional) After completing the preceding configuration, OSPF TI-LFA is enabled on all OSPF interfaces. If you do not want to enable OSPF TI-LFA on some interfaces, perform the following operations:
1. Run quit
  Exit the OSPF FRR view.
2. Run quit
  Exit the OSPF view.
3. Run interface interface-type interface-number
  The interface view is displayed.
4. To disable the OSPF TI-LFA on a specified interface, run either of the following commands:
  - For a common interface, run the ospf ti-lfa disable command.
  - For a multi-area interface, run the ospf ti-lfa disable multi-area area-id command.
If a network fault occurs or is rectified, an IGP performs route convergence. A transient forwarding status inconsistency between nodes results in different convergence rates on devices, posing the risk of microloops. To prevent microloops, perform the following steps:
1. Run quit
  Exit the interface view.
2. Run ospf [ process-id ]
  
  An OSPF process is created, and the OSPF view is displayed.
3. Run avoid-microloop frr-protected
  OSPF local microloop avoidance is enabled.
4. Run avoid-microloop frr-protected rib-update-delay rib-update-delay
  The delay after which OSPF delivers routes is configured.
5. Run avoid-microloop segment-routing
  
  OSPF remote microloop avoidance is enabled.
6. (Optional) Run avoid-microloop segment-routing rib-update-delay rib-update-delay
  
  A delay in delivering OSPF routes in an SR scenario is set.
Run commit
The configuration is committed.

Verifying the Configuration

After completing all OSPF TI-LFA FRR configurations, run the display ospf [ process-id ] segment-routing routing [ ip-address [ mask | mask-length ] ] command to check OSPF SR routing table information.