H3C Technologies H3C S6800 Series Switches - Manual (Page 36)

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{
LDP recovers to the state before the restart or switchover.
{
The maximum delay timer expires.
LDP FRR
A link or router failure on a path can cause packet loss until LDP completes LSP establishment on the new
path. LDP FRR enables fast rerouting to minimize the failover time. LDP FRR bases on IP FRR and is
enabled automatically after IP FRR is enabled.
You can use one of the following methods to enable IP FRR:
• Configure an IGP to automatically calculate a backup next hop.
• Configure an IGP to specify a backup next hop by using a routing policy.
Figure 14 Network diagram for LDP FRR
As shown in Figure 14 , configure IP FRR on LSR A. The IGP automatically calculates a backup next hop
or it specifies a backup next hop through a routing policy. LDP creates a primary LSP and a backup LSP
according to the primary route and the backup route calculated by IGP. When the primary LSP operates
correctly, it forwards the MPLS packets. When the primary LSP fails, LDP directs packets to the backup
LSP.
When packets are forwarded through the backup LSP, IGP calculates the optimal path based on the new
network topology. When IGP route convergence occurs, LDP establishes a new LSP according to the
optimal path. If a new LSP is not established after IGP route convergence, traffic forwarding might be
interrupted. Therefore, H3C recommends that you enable LDP IGP synchronization to work with LDP FRR
to reduce the traffic interruption time.
Protocols
RFC 5036, LDP Specification
LDP configuration task list
Tasks at a glance
Enable LDP:
1. (Required.) Enabling LDP globally
2. (Required.) Enabling LDP on an interface