Session protection is way to protect label bindings whenever a failure between to LDP peers goes down. It's enabled globally and forms targeted LDP session between two different LDP peers. The targeted session allows the LDP session to be maintained which allows the label database to be maintained. As long as a different path is available, if the "main" or primary path is not available, the targeted or multi-hop session will allow the label bindings to be maintained.

CSR1#show mpls ldp discovery 
 Local LDP Identifier:
    192.0.2.1:0
    Discovery Sources:
    Interfaces:
        GigabitEthernet1 (ldp): xmit/recv
            LDP Id: 192.0.2.3:0

CSRs
mpls ldp session protection

XRs
mpls ldp
 session protection

CSR1#show mpls ldp discovery 
 Local LDP Identifier:
    192.0.2.1:0
    Discovery Sources:
    Interfaces:
        GigabitEthernet1 (ldp): xmit/recv
            LDP Id: 192.0.2.3:0
    Targeted Hellos:
        192.0.2.1 -> 192.0.2.3 (ldp): active, xmit

CSR1#show mpls ldp discovery detail 
 Local LDP Identifier:
    192.0.2.1:0
    Targeted Hellos:
        192.0.2.1 -> 192.0.2.3 (ldp): active/passive, xmit/recv
        Enabled by: LDP SP, 
            Hello interval: 10000 ms; Transport IP addr: 192.0.2.1
            LDP Id: 192.0.2.3:0
              Src IP addr: 192.0.2.3; Transport IP addr: 192.0.2.3
              Hold time: 90 sec; Proposed local/peer: 90/90 sec
              Reachable via 192.0.2.3/32
              Password: not required, none, stale


RP/0/0/CPU0:XR11#show mpls ldp discovery 
Sat Sep 14 00:55:47.229 UTC

Local LDP Identifier: 192.0.2.11:0
Discovery Sources:
  Targeted Hellos:
    192.0.2.11 -> 192.0.2.2 (active), xmit/recv
      LDP Id: 192.0.2.2:0
          Hold time: 90 sec (local:90 sec, peer:90 sec)
          Established: Sep 14 00:53:38.787 (00:02:08 ago)

    192.0.2.11 -> 192.0.2.3 (active), xmit/recv
      LDP Id: 192.0.2.3:0
          Hold time: 90 sec (local:90 sec, peer:90 sec)
          Established: Sep 14 00:53:38.777 (00:02:08 ago)

    192.0.2.11 -> 192.0.2.6 (active), xmit/recv
      LDP Id: 192.0.2.6:0
          Hold time: 90 sec (local:90 sec, peer:90 sec)
          Established: Sep 14 00:53:38.787 (00:02:08 ago)