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DES-7200 Configuration Guide Chapter 3 MPLS Reliability Configuration
3-4
4) For some reason, LDP on LSR1 is restarted. LSR1 retains all MPLS forwarding data
added/maintained by LDP and mark them as "stale", and enables MPLS Forwarding State
Holding Timer.
5) The LDP GR-Capable LSR 2 detects that its GR-Capable LDP session with LSR 1 is
disconnected, and therefore retains the MPLS forwarding data related to this session and
marks them as "stale". Meanwhile, it will use the lesser value of Liveness Timer configured
and FT Reconnect Timeout in the FT Session TLV received to start the Liveness Timer, and
retains these "stale" forwarding data before the timer is triggered.
6) When LSR 1 reestablishes session with LSR 2, it will set the Recovery Time in FT Session
TLV carried by Initialization message to the residual value of MPLS Forwarding State
Holding Timer.
7) LSR 2 receives the Initialization message carrying FT Session TLV sent by LSR 1 and
detects that the Recovery Time is not 0. It will continue to retain the "stale" forwarding data
and stop Liveness Timer at the same time. Meanwhile, it will use the lesser value of
Recovery Timer configured and the Recovery Time in the FT Session TLV received to start
the Recovery Timer, and retains these "stale" forwarding data before the timer is triggered.
8) LSR 1 and LSR 2 re-exchange address information and label mapping information, and
remove or retain MPLS forwarding data marked as "stale" according to the information
exchanged.
9) GR process ends. LSR 1 and LSR 2 will delete their own MPLS forwarding data marked as
"stale".
Protocol specification
Related protocol specifications include:
z RFC3036: LDP Specification
z RFC3037: LDP Applicability
z RFC3215: LDP State Machine
z RFC3478: Graceful Restart Mechanism for Label Distribution Protocol
z RFC3479: Fault Tolerance for the Label Distribution Protocol (LDP)
3.1.1.2 Configure LDP GR
The following sections describe how to configure LDP GR: