ti-lfa (IS-IS FRR view)

Function

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

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

By default, 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 IS-IS Level-1 TI-LFA.	-
level-2	Enables or disables IS-IS Level-2 TI-LFA.	-
level-1-2	Enables or disables 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 IS-IS Level-1 TI-LFA.

level-2

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

level-1-2

Enables or disables 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 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 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 SR label forwarding table for traffic forwarding based on labels in the packet header.

Prerequisites

Global Segment Routing has been enabled using the segment-routing command.

FRR has been enabled and the FRR view has been displayed using the frr command, and 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 can take effect in a level-specific IS-IS area only after the level-specific LFA is enabled.

To allow the TI-LFA function to take effect, ensure that TI-LFA is enabled on an IS-IS interface. By default, TI-LFA is enabled on an IS-IS interface automatically.

Example

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

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