isis ldp-sync

Function

The isis ldp-sync command enables synchronization between LDP and IS-IS on an interface.

The undo isis ldp-sync command disables synchronization between LDP and IS-IS on an interface.

By default, synchronization between LDP and IS-IS is disabled on an interface.

Format

isis ldp-sync

undo isis ldp-sync

Parameters

None

Views

Interface view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

The LDP convergence speed depends on the convergence speed of IS-IS routes. To enable MPLS LDP on a network with the primary and backup links, the following problems may occur:

Upon a fault on the primary link, IS-IS routes and ISP are both switched to the backup link using LDP FRR. When the primary link recovers, IS-IS routes are switched back to the primary link earlier than LDP traffic because IGP route convergence is faster than LDP convergence. As a result, LSP traffic is lost.
If a fault occurs on the LDP session between nodes on the primary link where the IS-IS routes are working properly, the IS-IS routes still use the primary link and the LSP on the primary link is deleted. No IS-IS route exists on the backup link; therefore, no LSP can be established on the backup link. LSP traffic is lost.

Run the isis ldp-sync command to enable synchronization between LDP and IS-IS to prevent traffic loss in the preceding problems. Run this command on the interfaces on both ends of the link between the node where the primary LSP and the backup LSP diverge from each other and its LDP peer on the primary LSP.

Prerequisites

The IS-IS process has been started using the isis enable command in the interface view.

Example

# Enable synchronization between LDP and IS-IS on VLANIF100.

<HUAWEI> system-view
[HUAWEI] interface vlanif 100
[HUAWEI-Vlanif100] isis enable 1
[HUAWEI-Vlanif100] isis ldp-sync

# Enable synchronization between LDP and IS-IS on GE0/0/1.

<HUAWEI> system-view
[HUAWEI] interface gigabitethernet 0/0/1
[HUAWEI-GigabitEthernet0/0/1] undo portswitch
[HUAWEI-GigabitEthernet0/0/1] isis enable 1
[HUAWEI-GigabitEthernet0/0/1] isis ldp-sync