I wanted to lab up MPLS LDP session protection to reduce the time needed for LDP convergence in the event of a link failure. However, having targeted hellos is a prerequisite. So lets configure it.

Still working off the same topology, I’ll set up and test targeted hello sessions between PE_WEST and P1.

First I am going to shut down the link a P1 towards PE_WEST. The LDP neighbors drop as expected.

P1(config)#int fa1/0
4d01h: %OSPF-5-ADJCHG: Process 1, Nbr on FastEthernet1/0 from FULL to DOWN, Neighbor Down: Interface down or detached
4d01h: %LDP-5-NBRCHG: LDP Neighbor is DOWN

3d22h: %LDP-5-NBRCHG: LDP Neighbor is DOWN

Even though that link is down, connectivity between the loopbacks still work fine.

PE_WEST#ping so lo0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Packet sent with a source address of

I brought the link back up, and configured targeted hellos between PE_WEST and P1

PE_WEST(config)#mpls ldp neigh targeted ldp

P1(config)#mpls ldp neigh targeted ldp

Now shutting down the link again, the neighbors stay up.

P1#show ip int fa1/0 | i 1/0
FastEthernet1/0 is administratively down, line protocol is down

P1#show mpls ldp neighbor detail
Peer LDP Ident:; Local LDP Ident
TCP connection: -
State: Oper; Msgs sent/rcvd: 35/32; Downstream; Last TIB rev sent 34
Up time: 00:13:26; UID: 10; Peer Id 0;
LDP discovery sources:
Targeted Hello ->, active, passive;
holdtime: infinite, hello interval: 10000 ms
Addresses bound to peer LDP Ident:
Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab
Clients: Dir Adj Client

PE_WEST#show mpls ldp discovery
 Local LDP Identifier:
    Discovery Sources:
        FastEthernet2/0 (ldp): xmit/recv
        FastEthernet2/1 (ldp): xmit/recv
            LDP Id:
    Targeted Hellos: -> (ldp): active/passive, xmit/recv
            LDP Id:

In the output shows the targeted hello between <-> Turn debug up and verify the transport protocol and port for these hellos.

PE_WEST(config)#access-list 103 permit ip host host
PE_WEST(config)#access-list 103 permit ip host host

PE_WEST#debug ip packet detail 103

3d22h: IP: s= (FastEthernet2/1), d=, len 62, rcvd 23d22h:     UDP src=646, dst=646
3d22h: IP: s= (FastEthernet2/1), d=, len 62, stop process pak for forus packet
3d22h:     UDP src=646, dst=646
3d22h: IP: s= (local), d= (FastEthernet2/1), len 62, sending
3d22h:     UDP src=646, dst=646
3d22h: IP: s= (FastEthernet2/1), d=, len 62, rcvd 2
3d22h:     UDP src=646, dst=646

It used UDP with src/dst port for the hellos as before. Only instead of the all routers multicast address they are targeted.

With targeted hellos working, next post I can MPLS LDP session protection.