GR helper LSR restarting procedure

When the LSR detects that its LDP session with a neighbor is down and the neighbor is capable of preserving its forwarding state, the LSR does the following:

1. Retains the label-FEC bindings received by way of the session and marks them as stale.
2. Starts the Reconnect timer with the timeout value set to the lesser of the peer FT Reconnect Timeout and the locally configured maximum Reconnect timeout.
3. Attempts to re-establish the LDP session with the neighbor using the normal LDP procedure. All the stale label-FEC bindings are deleted when either condition is true:
   • The Reconnect timer has expired and the LDP session to the neighbor is not established.
   • The LSR receives FT TLV in the Initialization message from the neighbor and the FT Recovery Time is set to 0.

   After the session is re-established, the LDP GR helper resends the Label Mappings to its neighbor. For the stale label-FEC bindings received from the neighbor, they are recovered during the recovery period which is set to the lesser of the peer Recovery Timeout and the locally configured maximum recovery time. If the stale entries are not recovered after the Recovery Timer has expired, they are deleted.