Junos Cup 2014
Junos Cup 2014

Tournament 1: Russia Challenge & Solution - MPLS BGP Traffic Drop

[ Edited ]
‎06-12-2014 07:36 AM

Country Flag associated with this challenge: RUSSIA


Author: Alexander Arseniev


Title: MPLS BGP Traffic Drop


Type: Service Provider


Difficulty: High (2 points).


Technical Description: Configure PE1 so that, in case MPLS is not functional between PE1 and P, PE1 drops the traffic towards instead of sending it unlabeled to P.


Challenge Instructions:

For this challenge, you need to start the topology called: “RUSSIA – MPLS BGP Traffic Drop”


Here is the physical topology:




Initially, MPLS is fully functional across the network and traceroute from PE1 to shows a labeled path:


juniper@PE1> traceroute

traceroute to (, 30 hops max, 40 byte packets

 1 (  24.296 ms  19.110 ms  20.235 ms

     MPLS Label=299776 CoS=0 TTL=1 S=1

 2 (  29.297 ms  29.794 ms  20.349 ms


Now if you disrupt MPLS between PE1 and P, for example, by configuring the following at P:


juniper@P> configure                           

juniper@P# deactivate protocols rsvp

juniper@P# commit and-quit


And executing the following at PE1:


juniper@PE1> clear mpls lsp


Then traceroute now shows that traffic is being dropped by P:


juniper@PE1> traceroute   

traceroute to (, 30 hops max, 40 byte packets

 1 (  24.330 ms !N  18.815 ms !N  20.235 ms !N


You need to configure PE1 so that, if MPLS is not functional between PE1 and P, the traffic destined to is dropped by PE1 and never sent to P. In that case, traceroute should look like this:


juniper@PE1> traceroute   

traceroute to (, 30 hops max, 40 byte packets

traceroute: sendto: No route to host

 1 traceroute: wrote 40 chars, ret=-1

 *traceroute: sendto: No route to host

traceroute: wrote 40 chars, ret=-1



And if MPLS is functional between PE1 and P, then traceroute should show a MPLS labeled path again.


To solve the challenge you need to submit just one configuration set command at PE1 like this:



set <...>

commit and-quit



NOTE: If you have issues connecting to the Junosphere topology please check Junosphere Technical documentation, or request assistance in the Junosphere forum 

Send an email with your proposed solution to junos-cup@juniper.net:

  •  The subject should be “<country-name-of-the-challenge> -  <your-full-name>”. For example: “Brazil – Wolfgang Amadeus Mozart”.
  • In the email body, please include your proposed solution, along with your first and last name and complete mailing address including zip/postal code and your shirt size (S, M, L, XL, XXL, XXXL)


Some additional notes:

  • Feel free to participate in as many challenges as you like, they are open to everyone and the more you participate the better chance of winning!
  • Green Planet Rules: please start one topology at a time, do not run several topologies in parallel and don't forget to stop your active topology when not in use
  • The answers will be read by the organization right after the deadline
  • The challenge instructions are final, and no additional information or tips will be provided before the publication of the solution and the winner list. Please don’t expect a reply from junos-cup@juniper.net.
  • If you feel that your initial solution is wrong or incomplete, you can send up to three messages for the same challenge, but please note that only your last message (received before the deadline) will be read.
  • If you think there is an error in the definition of the challenges, please send us an email with subject (“<country-name> ERROR”); if there is no reply, then it’s likely an intentional condition of the challenge, rather than an error.


At PE1:

set routing-options resolution rib inet.0 resolution-ribs inet.3



Julie Wider
Advocacy Manager
Twitter: @JNetCommunity & @jawider