Configuring IS-IS Auto FRR

This section describes how to configure IS-IS Auto FRR.

Usage Scenario

As networks develop, Voice over Internet Protocol (VoIP) and online video services pose increasingly higher requirements for real-time transmission. Nevertheless, if an IS-IS fault occurs, multiple operations, including fault detection, LSP updating, LSP flooding, route calculation, and forwarding information base (FIB) entry delivery, must be performed to switch traffic to a new link. These operations take a long time, much longer than 50 ms, the minimum delay to which users are sensitive. As a result, user experience is affected.

With IS-IS Auto FRR, devices can rapidly switch traffic from a faulty link to an alternate one without interrupting the traffic, which significantly improves IS-IS network reliability.

IS-IS Auto FRR is suitable for IP services that are sensitive to delay and packet loss.

Pre-configuration Tasks

Before configuring IS-IS Auto FRR, complete the following tasks:

Configure IP addresses for interfaces and ensure that neighboring devices are reachable at the network layer.
Configure basic IPv4 IS-IS functions.
Before you configure remote LFA FRR, configure LDP LSPs to perform recursion hop by hop between the source node and PQ node. That is, configure a local LDP session between each pair of directly connected nodes along the link from the source node to PQ node.

Procedure

Run system-view
The system view is displayed.
Run isis [ process-id ]
An IS-IS process is created, and the IS-IS view is displayed.
Run frr
The IS-IS FRR view is displayed.
(Optional) Run ecmp disable { level-1 | level-2 }
The IS-IS ECMP FRR function is disabled.

With ECMP FRR, IS-IS pre-calculates backup paths for load balancing links based on the LSDBs on the entire network. The backup paths are stored in the forwarding table and are used for traffic protection in the case of link failures. If the network topology changes, ECMP FRR triggers calculation of new backup paths, which increases the system calculation pressure. In addition, the backup entries generated by the ECMP FRR function increase the memory usage of the system. In this case, you can run the ecmp disable command to disable the ECMP FRR function.
Run loop-free-alternate [ level-1 | level-2 | level-1-2 ]
LFA is enabled for IS-IS Auto FRR.

If no IS-IS level is specified, LFA is enabled for both Level-1 and Level-2 IS-IS Auto FRR.

For details about IS-IS Auto FRR, see "Feature Description" > "IP Routing" in the HUAWEI NetEngine 8000 F SeriesRouter Product Documentation.

IS-IS can calculate the loop-free alternate route only if the traffic protection inequality of IS-IS Auto FRR is met.
(Optional) Run frr-policy route route-policy route-policy-name
A route-policy is configured to filter IS-IS alternate routes.
If you want to configure remote LFA Auto FRR, perform the following steps:
1. Run remote-lfa tunnel ldp [ maximum-reachable-cost cost-value ] [ level-1 | level-2 | level-1-2 ]
  Remote LFA Auto FRR is enabled.
2. (Optional) Run remote-lfa available-tunnel-destination ip-prefix ip-prefix-name [ level-1 | level-2 | level-1-2 ]
  A filtering policy is configured to filter PQ nodes.
  
  Only the PQ node that matches the filtering policy can be used as the next hop of an LFA link.
3. Run quit
  Return to the IS-IS view.
4. (Optional) Run avoid-microloop frr-protected
  The IS-IS anti-microloop function is enabled.
5. (Optional) Run avoid-microloop frr-protected rib-update-delay rib-update-delay
  The delay after which IS-IS delivers routes is configured.
  
  If IS-IS remote LFA FRR is enabled and the primary link fails, traffic is switched to the backup link. If route convergence occurs again, traffic is switched from the backup link to a new primary link. During the switchover, microloop may occur. To prevent this problem, IS-IS anti-microloop is enabled by delays the switching. To configure the delay, run the avoid-microloop frr-protected rib-update-delay rib-update-delay command. After the command is run, IS-IS does not switch traffic to the backup link until the delay expires.
  
  By default, the delay is 100 ms. Keeping the default delay is recommended.
6. Run frr
  Enter the IS-IS FRR view.
(Optional) Run tiebreaker { node-protecting | lowest-cost | non-ecmp | srlg-disjoint | hold-max-cost } preference preference [ level-1 | level-2 | level-1-2 ]
The solution of selecting a backup path for IS-IS Auto FRR is set.
(Optional) After the preceding steps are performed, all IS-IS interfaces will be calculated to select an LFA next hop. If you want to disable an interface from being calculated as an LFA next hop, perform the following steps:
1. Run quit
  Exit the IS-IS FRR view.
2. Run quit
  Exit the IS-IS view.
3. Run interface interface-type interface-number
  The interface view is displayed.
4. Run undo isis lfa-backup [ level-1 | level-2 | level-1-2 ]
  The interface is disabled from being calculated as an LFAor remote LFA next hop.
(Optional) Run isis remote-lfa disable [ level-1 | level-2 | level-1-2 ]
The system is prevented from calculating a remote LFA next hop for the IS-IS route whose outbound interface is the current interface.
Run commit
The configuration is committed.

Verifying the Configuration

After configuring IS-IS Auto FRR, check the configurations.

Run the display isis route [ level-1 | level-2 ] [ process-id ] [ verbose ] command to check information about the primary and alternate links after IS-IS Auto FRR is enabled.
Run the display isis spf-tree [ [ level-1 | level-2 ] | verbose ] ^* [ process-id | vpn-instance vpn-instance-name ] command to check SPT topology.
Run the display isis frr summary [ level-1 | level-2 | level-1-2 ] [ process-id ] command to view the FRR protection rates of routes in an IS-IS process.
Run the display isis [ process-id ] srlg { srlgGroupId | all } command to check shared risk link group (SRLG) information.