ldp neighbour not coming up

[Psmurali89]

Hi All 

Am tying to establish LDP neighbour between 2 devices but its not coming up.. Both sides saying they are sending and receiving but neighbour is not coming up.  In-between these 2 devices there are one Layer2 switch (Cisco 9200 Version 17.3.6) managed by us and a Layer3 ISP device. I can ping between those vlan's, BGP (i used BGP between these 2 VLAN's) and OSPF is up but just LDP is not coming up. 

Not sure if the issues is with those devices? Any help/suggestions is much appreciated. 

Router1: 

GigabitEthernet0/0/3.923 (ldp): xmit/recv
LDP Id: 192.168.240.42:0

Switch1: 

Vlan923 (ldp): xmit/recv
LDP Id: 192.168.249.2:0

SWITCH1#sh mpls ldp neighbour

ROUTER1#sh mpls ldp neighbour

[Psmurali89]

Details below. I have other LDP vlans in the same router switch but just this vlan is not working. 

As you can see below, LDP can see both sides but if i issue sh mpls ldp neighbour i dont get any output. 

Switch#sh mpls ldp discovery detail
Local LDP Identifier:
192.168.240.42:0
Discovery Sources:
Interfaces:
Vlan923 (ldp): xmit/recv
Enabled: Interface config
Hello interval: 5000 ms; Transport IP addr: 192.168.240.42
LDP Id: 192.168.249.2:0
Src IP addr: 192.168.240.45; Transport IP addr: 192.168.249.2
Hold time: 15 sec; Proposed local/peer: 15/15 sec
Reachable via 192.168.249.2/32
Password: not required, none, in use
Clients: IPv4, mLDP

==========================

Router#sh mpls ldp discovery detail
Local LDP Identifier:
192.168.249.2:0
Discovery Sources:
Interfaces:
GigabitEthernet0/0/3.923 (ldp): xmit/recv
Enabled: Interface config
Hello interval: 5000 ms; Transport IP addr: 192.168.249.2
LDP Id: 192.168.240.42:0
Src IP addr: 192.168.240.46; Transport IP addr: 192.168.240.42
Hold time: 15 sec; Proposed local/peer: 15/15 sec
Reachable via 192.168.240.40/30
Password: not required, none, in use
Clients: IPv4, mLDP

[MHM Cisco World]

192.168.240.40/30 <<- this not OK, I dont now sure why but the LDP only accept neighbor with /31 & /32 router-ID, not /30 
so you have two solution as I mention before,
config transport 
config LO use it as router-ID 
192.168.249.2/32 <<- this OK, you can use it as Router-ID 

[Psmurali89]

Hi, Thank you. 

I think you are right.. I will force the LDP in Switch to use /32 loopback. I think its taken the VLAN IP of /30 instead of /32 loopback. 

I will do this next week and update. 

[MHM Cisco World · Accepted solution]

MPLS – Transport-Address vs LDP Router-ID (RID), how they are tied together, and how to configure them to differ, and how that can help “engineer” the network! – The DEVNET GRIND! (loopedback.com)

more about the router-id and transport-address 
thanks 
MHM

[Psmurali89]

Hi, 

So I forced the LDP id to /32 loopback address and the LDP neighbour came up. 

Thank you for your help. 

[MHM Cisco World]

You are so welcome 
and thanks you update us. 
have a nice day