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)
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)