isis ldp-sync

Function

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

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

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

Format

isis ldp-sync

undo isis ldp-sync

Parameters

None

Views

Ethernet interface view, Ethernet sub-interface view, Eth-Trunk interface view, Eth-Trunk sub-interface view, Tunnel interface view, Loopback interface view, Dialer interface view, VLANIF interface view, Virtual-Template interface view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

LDP convergence depends on IS-IS route convergence. Therefore, LDP converges slower than IS-IS routes. When MPLS LDP is used on a network with active and standby links, one of the following problems may occur:

When the active link is faulty, traffic forwarded over the IS-IS route and label switched path (LSP) is switched to the standby link. When the active link recovers, traffic forwarded over the IS-IS route is switched back to the active link earlier than the LSP. As a result, LSP traffic is lost.
When IS-IS is working properly over the active link but an LDP session over the active link goes Down, the IS-IS route still uses the active link, while the LSP is deleted from the active link. Meanwhile, the LSP fails to be established over the standby link because the standby link is not an optimal IS-IS route. As a result, LSP traffic is lost.

To prevent traffic loss in the preceding situations, run the isis ldp-sync command to enable LDP and IS-IS synchronization on an interface of the crossing node of the active and standby links.

LDP-Interior Gateway Protocol (IGP) synchronization delays IGP route advertisement so that the LDP session and IGP route can converge simultaneously.

Prerequisites

An IS-IS process has been configured using the isis enable command in the interface view.

Example

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

<sysname> system-view

[sysname] interface GigabitEthernet 0/0/0

[sysname-GigabitEthernet0/0/0] isis enable

[sysname-GigabitEthernet0/0/0] isis ldp-sync