Cisco ASR 900 Series User Manual

Prerequisites for NSR LDP Support
The Label Distribution Protocol (LDP) must be up and running on the standby Route Processor (RP) for NSR
LDP Support to work.
Information About NSR LDP Support
Roles of the Standby Route Processor and Standby LDP
For the NSR LDP Support feature to work, the Label Distribution Protocol (LDP) must be up and running on
the standby Route Processor (RP). The LDP component running on the active RP is called the active LDP,
and the LDP component running on the standby RP is called the standby LDP.
When nonstop routing (NSR) is enabled, the standby LDP runs independently from the active LDP, but with
the assistance of some software components. The standby LDP maintains LDP session states and database
information, ready to take over for the active LDP if the failover occurs.
Standby LDP maintains its local database by querying or receiving notifications of interface status change,
configuration changes from the CLI, and checkpoints from the active LDP for other information that is not
directly available on the standby RP.
To keep the protocol and session-state information synchronized with the active LDP, the standby LDP
depends on TCP to replicate all LDP messages on the active RP to the standby RP. The standby LDP processes
all received messages, updates its state, but does not send any responses to its neighbors.
The standby LDP performs the following tasks:
•
Processes LDP configuration on startup and during steady state
•
Processes active LDP checkpoints of state and session information such as LDP adjacencies, remote
addresses, remote bindings, and so forth
•
Builds its database of local interfaces
•
Processes interface change events
•
Receives and processes all LDP messages replicated by TCP
•
Updates remote address and label databases
After a switchover and notification that the RP has become active, the standby LDP takes over the role of the
active LDP and performs the following tasks:
•
Sends hello messages immediately to prevent neighbors from reaching the discovery timeout and bringing
down the session
•
Retransmits any protocol-level response that has not been sent by the previous active LDP
•
Readvertises label bindings
•
Refreshes all forwarding entries
•
Processes and responds to any LDP message from its neighbor
MPLS Basic Configuration Guide, Cisco IOS XE Everest 16.5.1 (Cisco ASR 900 Series)
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NSR LDP Support
Prerequisites for NSR LDP Support

Cisco ASR 900 Series Specifications

General

Brand	Cisco
Model	ASR 900 Series
Category	Network Router
Language	English