LDP Session -- "Nonexistent"

[JoeM]

Hello, Cisco guy here, who is being thrown into the Alcatel world.
Need help with an LDP neighbor issue. Apologies if I am posting this in the wrong sub-forum.

Thanks in advance for any help with this.

Platform: VSR-SIM (7750) - TiMOS-B-12.0.R6
(unlicensed reboots every 60 minutes -- working on getting a license)

Using Workbook: Alcatel-Lucent Scalable IP Networks Self-Study Guide

ISSUE: LDP session is showing "Nonexistent"
* IGP is IS-IS and connectivity is good.
* LDP session recognizes the neighbor system-id
* both neighbors can ping each other (but same results on each side)



A:VSR-SIM-2# show router ldp interface
===============================================================================
LDP Interfaces
===============================================================================
Interface Adm Opr Hello Hold KA KA Transport
Factor Time Factor Timeout Address
-------------------------------------------------------------------------------
toSR3 Up Up 3 15 3 30 System
toSR4 Up Up 3 15 3 30 System
-------------------------------------------------------------------------------
No. of Interfaces: 2
===============================================================================



A:VSR-SIM-2# show router ldp session
==============================================================================
LDP Sessions
==============================================================================
Peer LDP Id Adj Type State Msg Sent Msg Recv Up Time
------------------------------------------------------------------------------
3.3.3.3:0 Link Nonexistent 1 2 0d 00:00:05
------------------------------------------------------------------------------
No. of Sessions: 1
==============================================================================
A:VSR-SIM-2#

[thekotaksampah]

Could you share your topology. in your IS-IS interface. Have you put interface system in it? and make sure the interface system is up.

I have example topology:

SITE-B |--------------------------|SITE-C


And My Configuration like this
SITE-C

Code: Select all

*B:SITE-ALU-C>config>router>isis# info 
----------------------------------------------
        level-capability level-1
        area-id 49.1000
        interface "system"
            no shutdown
        exit
        interface "to-SITE-B"
            level-capability level-1
            interface-type point-to-point
            no shutdown
        exit
        no shutdown
----------------------------------------------
*B:SITE-ALU-C>config>router>isis#

In SITE-B

Code: Select all

*A:SITE-ALU-B>config>router>isis# info 
----------------------------------------------
        level-capability level-1
        area-id 49.1000
        interface "system"
            no shutdown
        exit
        interface "to-SITE-C"
            level-capability level-1
            interface-type point-to-point
            no shutdown
        exit
        no shutdown
----------------------------------------------
*A:SITE-ALU-B>config>router>isis# 

I check the ldp session

Code: Select all

*B:SITE-ALU-C# /show router ldp session 

==============================================================================
LDP Sessions
==============================================================================
Peer LDP Id        Adj Type   State         Msg Sent  Msg Recv  Up Time
------------------------------------------------------------------------------
192.168.200.2:0    Both       Established   153       157       0d 00:05:28
------------------------------------------------------------------------------
No. of Sessions: 1
==============================================================================

But when you forget to put interface system or shutdown it, in ISIS router configuration:

Code: Select all

*B:SITE-ALU-C>config>router>isis# info 
----------------------------------------------
        level-capability level-1
        area-id 49.1000
        interface "system"
            shutdown
        exit
        interface "to-SITE-B"
            level-capability level-1
            interface-type point-to-point
            no shutdown
        exit
        no shutdown
----------------------------------------------
*B:SITE-ALU-C>config>router>isis# 

*B:SITE-ALU-C>config>router>isis# /show router isis interface 

===============================================================================
Router Base ISIS Instance 0 Interfaces
===============================================================================
Interface                        Level CircID  Oper State   L1/L2 Metric
-------------------------------------------------------------------------------
system                           L1L2  1       Down         0/0
to-SITE-B                        L1    2       Up           10/-
-------------------------------------------------------------------------------
Interfaces : 2
===============================================================================
*B:SITE-ALU-C>config>router>isis# 

You find the ldp session notexistent

Code: Select all

*B:SITE-ALU-C# show router ldp session 

==============================================================================
LDP Sessions
==============================================================================
Peer LDP Id        Adj Type   State         Msg Sent  Msg Recv  Up Time
------------------------------------------------------------------------------
192.168.200.2:0    Link       Nonexistent   2         2         0d 00:00:06
------------------------------------------------------------------------------
No. of Sessions: 1
==============================================================================
*B:SITE-ALU-C# 

I hope this answer can solve your problem. Thanks

[JoeM]

Thanks for the reply. I had fixed this, but needed to wait for my original post to be moderated. But for sure, I will start using this forum. I have a lot of studying to do, so that I can transfer cisco skills to alcatel.

The fix: advertise the "system" interface into the IGP. The LDP session came up immediately.

I did have the interface 'system' up, but it was not advertised to the other routers.

Thanks again.

[mivens]

Yep, the output suggests LDP discovery has completed but it has not been possible to bring up the LDP transport session between the two system addresses learnt from the LDP discovery.

Check the system addresses are reachable (usually achieved by making sure the system interface is in ISIS). Can you ping between the two system addresses for example?

[thecandymancan]

LDP establishes its TCP session between the system address by default so as has been pointed out you cannot form a TCP session without reachability of the system address of each node. If you look at the debug router ldp ipv4 packet hello detail you will see when set as default the transport address is the system address. If you set it using conf router ldp ipv4 transport interface then it will use the link local address. If you do this on both sides you will form a TCP session and your show router ldp session will show established. the downside here is if that link goes down then bye bye LDP