LSR restarting procedure

After an LSR restarts its LDP components, when its MPLS forwarding state is not preserved as in the case of the routers in helper-only mode, it sends out the FT TLV with Recovery Time set to 0 in the LDP Initialization message to its neighbor.

When the MPLS forwarding state has been preserved across the restart, the LSR does the following:

  1. Start the Forwarding State Holding timer.
  2. Mark all the MPLS forwarding entries as stale.
  3. Set the Recovery Time to the current value of the Forwarding State Holding timer when it sends out LDP Initialization message to its neighbor.
    • When the timer has not expired, the LSR uses the labels and next-hop information received from the neighbor to look up and clear the stale flag for the corresponding label-FEC entries.
    • When the timer has expired, all the entries that are still marked as stale are deleted and the LDP GR procedure is completed.