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Command Reference

CloudEngine 8800, 7800, 6800, and 5800 V200R002C50

This document describes all the configuration commands of the device, including the command function, syntax, parameters, views, default level, usage guidelines, examples, and related commands.
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loop-free-alternate (OSPFv3 FRR)

loop-free-alternate (OSPFv3 FRR)

Function

The loop-free-alternate command enables OSPFv3 IP FRR and generates a loop-free backup route.

The undo loop-free-alternate command disables OSPFv3 IP FRR.

By default, OSPFv3 IP FRR is disabled.

Format

loop-free-alternate

undo loop-free-alternate

Parameters

None

Views

OSPFv3 FRR view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

Loop Free Alternate (LFA) is a method of implementing FRR. With LFA, a device can generate a loop-free backup link for FRR. OSPFv3 IP FRR takes effect only after the loop-free-alternate command is run.

To implement OSPFv3 IP FRR over specified routes, run the frr-policy route route-policy route-policy-name command to configure an OSPFv3 IP FRR filtering policy so that only the OSPFv3 backup routes that match the filtering conditions of the policy can be added to the forwarding table. If the primary link fails, OSPFv3 can switch traffic to the backup link immediately.

OSPFv3 LFA FRR uses the SPF algorithm to calculate the shortest path from each neighbor (root node) that provides a backup link to the destination node and store the node-based backup next hop, which applies to single-source routing scenarios. As networks are increasingly diversified, two ABRs or ASBRs are deployed to improve network reliability. In this case, OSPFv3 FRR in a multi-source routing scenario is needed. In Figure 9-2, Switch B and Switch C function as ABRs to forward area 0 and area 1 routes. Switch E advertises an intra-area route. Upon receipt of the route, Switch B and Switch C translate it to a Type 3 LSA and flood the LSA to area 0. After OSPFv3 FRR is enabled on Switch A, Switch A considers Switch B and Switch C as its neighbors. Without a fixed neighbor as the root node, Switch A fails to calculate FRR backup next hop. To address this problem, a virtual node is simulated between Switch B and Switch C and used as the root node of Switch A, and Switch A uses the LFA algorithm to calculate the backup next hop. This solution converts multi-source routing into single-source routing.
Figure 9-2  OSPFv3 FRR in a multi-route source scenario

Prerequisites

An OSPFv3 FRR view has been created and the system has entered the OSPFv3 FRR view using the frr command.

Precautions

To prevent a link over which important services are transmitted from being calculated for the backup link during route selection, run the ospfv3 frr block command on the interface connecting to the link before configuring the OSPFv3 IP FRR function.

Example

# Enable OSPFv3 IP FRR through LFA.

<HUAWEI> system-view
[~HUAWEI] ospfv3
[*HUAWEI-ospfv3-1] frr
[*HUAWEI-ospfv3-1-frr] loop-free-alternate
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Updated: 2019-03-21

Document ID: EDOC1000166501

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