Ldp Frr - HP FlexNetwork 10500 Series Configuration Manual

After LDP-IGP synchronization is enabled, IGP advertises the actual cost of a link only when LDP
convergence on the link is completed. Before LDP convergence is completed, IGP advertises the
maximum cost of the link. In this way, the link is visible on the IGP topology, but IGP does not select
this link as the optimal route when other links are available. Therefore, the device can avoid
discarding MPLS packets when there is not an LDP LSP established on the optimal route.
LDP convergence on a link is completed when both the following situations occur:
•
The local device establishes an LDP session to a minimum of one peer, and the LDP session is
already in Operational state.
•
The local device has distributed the label mappings to a minimum of one peer.
Notification delay for LDP convergence completion
By default, LDP immediately sends a notification to IGP that LDP convergence has completed.
However, immediate notifications might cause MPLS traffic forwarding interruptions in one of the
following scenarios:
•
LDP peers use the Ordered label distribution control mode. The device has not received a label
mapping from downstream at the time LDP notifies IGP that LDP convergence has completed.
•
A large number of label mappings are distributed from downstream. Label advertisement is not
completed when LDP notifies IGP that LDP convergence has completed.
To avoid traffic forwarding interruptions in these scenarios, configure the notification delay. When
LDP convergence on a link is completed, LDP waits before notifying IGP.
Notification delay for LDP restart or active/standby switchover
When an LDP restart or an active/standby switchover occurs, LDP takes time to converge, and LDP
notifies IGP of the LDP-IGP synchronization status as follows:
•
If a notification delay is not configured, LDP immediately notifies IGP of the current
synchronization states during convergence, and then updates the states after LDP
convergence. This could impact IGP processing.
•
If a notification delay is configured, LDP notifies IGP of the LDP-IGP synchronization states in
bulk when one of the following events occurs:
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 establishes a new LSP on the new
path. LDP FRR enables fast rerouting to minimize the failover time. LDP FRR is based 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.
As shown in
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. As a best practice, enable LDP-IGP synchronization to work with LDP FRR to
reduce traffic interruption.
Figure 14, configure IP FRR on LSR A. The IGP automatically calculates a backup next
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