ti-lfa (IS-IS IPv6 FRR view)

Function

The ti-lfa command enables IPv6 IS-IS topology independent-loop free alternate (TI-LFA).

The undo ti-lfa command disables IPv6 IS-IS TI-LFA.

By default, IPv6 IS-IS TI-LFA is disabled.

Format

ti-lfa [ level-1 | level-2 | level-1-2 ]

undo ti-lfa [ level-1 | level-2 | level-1-2 ]

Parameters

Parameter	Description	Value
level-1	Enables or disables IPv6 IS-IS Level-1 TI-LFA.	-
level-2	Enables or disables IPv6 IS-IS Level-2 TI-LFA.	-
level-1-2	Enables or disables IPv6 IS-IS Level-1-2 TI-LFA. If no level is specified, IS-IS Level-1-2 TI-LFA is enabled by default.	-

Parameter

Description

Value

level-1

Enables or disables IPv6 IS-IS Level-1 TI-LFA.

level-2

Enables or disables IPv6 IS-IS Level-2 TI-LFA.

level-1-2

Enables or disables IPv6 IS-IS Level-1-2 TI-LFA.

If no level is specified, IS-IS Level-1-2 TI-LFA is enabled by default.

Views

IS-IS IPv6 FRR view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
isis	write

Usage Guidelines

Usage Scenario

In some LFA or RLFA scenarios, the P space and Q space do not share nodes or have direct neighbors. If a link or node fails, no backup path can be calculated, causing traffic loss and a failure to meet reliability requirements.

To satisfy network reliability requirements, TI-LFA is configured to pre-calculate backup links. If a fault occurs, traffic rapidly switches to a backup link before convergence on the control plane is complete. The TI-LFA algorithm is used to calculate the backup links. This algorithm excludes the next hop on the primary LSP or the primary link, re-calculates a shortest path tree (also called a post-convergence tree), and selects a P node and a Q node along the tree. Based on the P and Q node information (see IPv6 TI-LFA FRR), a label stack for a backup tunnel is generated, directing traffic to be forwarded to the Q node through the tunnel. Upon receipt of a packet, the Q node searches the SRv6 label forwarding table for traffic forwarding based on labels in the packet header.

Prerequisites

Segment Routing IPv6 forwarding has been enabled using the segment-routing ipv6 command.

FRR has been enabled and the IPv6 FRR view has been displayed using the ipv6 frr command, and IPv6 IS-IS LFA has been enabled using the loop-free-alternate command.

Precautions

The level specified in the ti-lfa command depends on the level configured in the loop-free-alternate command. TI-LFA configured using the ti-lfa command can take effect in a level-specific IS-IS area only after the level-specific LFA is enabled.

Example

# Enable IPv6 IS-IS Level-2 TI-LFA.

<HUAWEI> system-view
[~HUAWEI] isis 1
[*HUAWEI-isis-1] ipv6 enable
[*HUAWEI-isis-1] cost-style wide
[*HUAWEI-isis-1] ipv6 frr
[*HUAWEI-isis-1-ipv6-frr] loop-free-alternate level-2
[*HUAWEI-isis-1-ipv6-frr] ti-lfa level-2