2.8 Configuring Synchronization Between LDP and Static
Routes
By configuring synchronization between LDP and static routes, you can switch traffic from a
faulty primary link to the backup link by suppressing the activation of static routes. You can
also delay traffic switchback to synchronize LDP and static routes.
2.8.1 Establishing the Configuration Task
Before configuring synchronization between LDP and static routes, familiarize yourself with
the applicable environment, complete the pre-configuration tasks, and obtain the required data.
Applicable Environment
Synchronization between LDP and static routes is applicable to an MPLS network with primary
and backup LSPs. On this type of MPLS network, LSRs establish LSPs based on static routes.
When the LDP session of the primary link becomes faulty (the fault is not caused by a link
failure) or the primary link recovers, synchronization between LDP and static routes minimizes
traffic loss during traffic switchover and switchback. As shown in Figure 2-2, there is a static
route between LSRA and LSRD, and an LSP is established between the two devices based on
the static route. Normally, the link LSRA→LSRB→LSRD is preferred.
l In a switchover scenario, when the LDP session of the primary link becomes faulty (the
fault is not caused by a link failure), traffic transmitted through the static route is not
switched to the backup link. As a result, MPLS traffic on the primary link is interrupted.
Normally, after an LDP session is established, MPLS traffic is forwarded along the primary
link LSRA→LSRB→LSRD. If the LDP session between LSRA and LSRB is disconnected,
the LSP is immediately switched to the backup link LSRA→LSRC→LSRD. Because the
link between LSRA and LSRB works properly, traffic transmitted through the static route
is not switched to the backup link. As a result, LDP is not synchronous with the static route,
and MPLS traffic is interrupted.
After synchronization between LDP and static routes is enabled, when the LDP session
goes Down, traffic is automatically switched to the backup link, ensuring non-stop traffic
forwarding.
l In a switchback scenario, when the primary link recovers, traffic transmitted through a
static route is first switched back to the primary link because the static route converges
faster than LDP. However, the backup LSP becomes unavailable, and the primary LSP has
not been established. As a result, MPLS traffic is interrupted.
When the link between LSRA and LSRB becomes faulty, traffic is immediately switched
to the backup link LSRA→LSRC→LSRD. After the link between LSRA and LSRB
recovers, traffic transmitted through the static route is immediately switched to the primary
link LSRA→LSRB→LSRD. However, the backup LSP becomes unavailable, and the
primary LSP has not recovered. Therefore, traffic is interrupted.
After synchronization between LDP and static routes is enabled, when the primary LSP is
established, traffic is switched back to the primary link, ensuring non-stop traffic
forwarding.
Huawei AR1200 Series Enterprise Routers
Configuration Guide - MPLS 2 MPLS LDP Configuration
Issue 01 (2011-12-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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