Cisco CRS Configuration Manual page 31

Implementing MPLS Label Distribution Protocol
Control communication failure detection
Control communication failure is detected when the system detects either:
Forwarding state maintenance during failure
Persistent forwarding states at each LSR are achieved through persistent storage (checkpoint) by the
LDP control plane. While the control plane is in the process of recovering, the forwarding plane keeps
the forwarding states, but marks them as stale. Similarly, the peer control plane also keeps (and marks
as stale) the installed forwarding rewrites associated with the node that is restarting. The combination
of local node forwarding and remote node forwarding plane states ensures NSF and no disruption in
the traffic.
Control state recovery
Recovery occurs when the session is reestablished and label bindings are exchanged again. This process
allows the peer nodes to synchronize and to refresh stale forwarding states.
Related Topics
Setting Up LDP NSF Using Graceful Restart, on page 43
Configuring LDP Nonstop Forwarding with Graceful Restart: Example, on page 82
• Missed LDP hello discovery messages
• Missed LDP keepalive protocol messages
• Detection of Transmission Control Protocol (TCP) disconnection a with a peer
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
LDP Graceful Restart
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