Junos Cup 2014
Junos Cup 2014

Tournament 1: USA Challenge & Solution -The Flapping Ping

[ Edited ]
‎06-12-2014 07:53 AM

Country Flag associated with this challenge: USA


Author: Krzysztof Szarkowicz


Title: The Flapping Ping


Type: Enterprise


Difficulty: High (2 points).


Technical Description: Fix an intermittent ping failure with a single configuration command.




Challenge Instructions:

For this challenge, you need to start the topology called: “USA – The Flapping Ping”.


As you can see here, the ping between the loopbacks of CE1A and CE2A is working fine:


juniper@CE1A> ping count 200 

PING ( 56 data bytes

/* output omitted */


--- ping statistics ---

200 packets transmitted, 200 packets received, 0% packet loss

round-trip min/avg/max/stddev = 21.575/30.760/41.044/2.037 ms


However, the ping between the loopbacks of CE1B and CE2B reports some loss:


juniper@CE1B> ping count 200          

PING ( 56 data bytes

/* output omitted */


--- ping statistics ---

200 packets transmitted, 136 packets received, 32% packet loss

round-trip min/avg/max/stddev = 20.982/31.530/57.074/4.028 ms


In order to solve this challenge, you must fix the issue so that both ping operations above are 100% successful:

- Between loopbacks of CE1A and CE2A

- Between loopbacks of CE1B and CE2B


And you must do it with a single set command on a single router of your choice, similar to this example:



<set command>  /* load is not permitted */

commit and-quit


Your solution must work after reboot of any router or routers. Further, your configuration change has these requirements:

-       If you execute show | compare before committing the configuration, there should not be any line preceded by the minus (-) sign.

-       You cannot change (explicitly configured or default) advertisement policies (IGP/BGP/LDP)


To solve this challenge, please provide the name of the router and the set command required to make both ping operations work.


 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.


Configure at CE1B:

juniper@CE1B# set interfaces ge-0/0/1 mtu 1400


Julie Wider
Advocacy Manager
Twitter: @JNetCommunity & @jawider