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[Junos] Intermediate hops are not displayed when performing a VRF traceroute on MPLS Label Switch Routers

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Article ID: KB33636 KB Last Updated: 01 May 2019Version: 1.0
Summary:

When attempting to perform a VRF traceroute, it will not display the intermediate hops for the L3VPNs.

Symptoms:

In many L3VPN troubleshooting situations, you want to know the intermediate hops in the path. In the following topology, P devices (R1, R2 and R3) have no specific details about VRF RED, therefore a VRF traceroute appears incomplete:



  .1 ------ .1           .2  ------  .2           .3 ------ 
    |  R1  |----------------|  R2  |----------------|  R3  |
     ------   10.10.12.0/24  ------  10.10.23.0/24   ------ 
    .1 |                                             .1 |  
       |  10.10.11.0/24                                 |  10.10.22.0/24
  .100 |                                           .100 |  
     ------                                          ------             
    |  PE1 |                                        |  PE2 |
     ------                                          ------   
       | .1                                             | .1
       | VRF: RED                                       | VRF: RED
       |                                                |
  172.16.1.0/30                                    172.16.2.0/30


user@PE1> traceroute 172.16.2.1 routing-instance RED 
traceroute to 172.16.2.1 (172.16.2.1), 30 hops max, 48 byte packets
 1  * * *
 2  * * *
 3  * * *
 4  172.16.2.1 (172.16.2.1)  0.800 ms  2.313 ms  0.712 ms
Cause:

By default, a VRF traceroute will not show the hops in the MPLS network without the proper configuration.

Solution:

Next knob must be configured in the P routers under protocols MPLS. For this example, we need to configure it in R1, R2 and R3 routers. 

"set protocols mpls icmp-tunneling"

After the knob is added in all the P routers, all the hops are seen.


user@PE1> traceroute 172.16.2.1 routing-instance RED    
traceroute to 172.16.2.1 (172.16.2.1), 30 hops max, 48 byte packets
 1  10.10.11.1 (10.10.11.1)  0.967 ms  1.619 ms  1.649 ms
     MPLS Label=16 CoS=0 TTL=1 S=0
     MPLS Label=16 CoS=0 TTL=1 S=1
 2  10.10.12.2 (10.10.12.2)  3.351 ms  0.746 ms  0.714 ms
     MPLS Label=299776 CoS=0 TTL=1 S=0
     MPLS Label=16 CoS=0 TTL=2 S=1
 3  10.10.23.3 (10.10.23.3)  1.100 ms  0.853 ms  0.748 ms
     MPLS Label=16 CoS=0 TTL=1 S=0
     MPLS Label=16 CoS=0 TTL=3 S=1
 4  172.16.2.1 (172.16.2.1)  0.703 ms  0.715 ms  0.697 ms
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