Cisco CRS Configuration Guide

Control communication failure detection
Control communication failure is detected when the system detects either:
•
Missed LDP hello discovery messages
•
Missed LDP keepalive protocol messages
•
Detection of Transmission Control Protocol (TCP) disconnection a with a peer
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
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
13
Implementing MPLS Label Distribution Protocol
LDP Graceful Restart

Cisco CRS Specifications

General

Operating System	Cisco IOS XR
Product Type	Core Router
Form Factor	Modular Chassis
Dimensions	Varies by chassis type
Weight	Varies by chassis type
Architecture	Distributed
Switch Fabric	Multi-stage
Interface Support	Ethernet, SONET/SDH, OTN
Interfaces/Ports	Varies by line card
Port Density	Varies by line card
Routing Protocol	BGP, IS-IS, OSPF, MPLS
Management	CLI, SNMP
Power Supply	Redundant, hot-swappable
Cooling	Redundant, Hot-swappable Fan Trays
Supported Protocols	IPv4, IPv6, MPLS
Management Interfaces	Ethernet, console
Security Features	ACLs