Junos Cup 2014
Junos Cup 2014

Tournament 2: Japan Challenge & Solution: Bridging with Virtual Switches

[ Edited ]
‎06-19-2014 07:38 AM

Country Flag: JAPAN


Author: Antonio Sánchez-Monge


Title: Bridging with Virtual Switches


Type: Enterprise


Difficulty: High (2 points).


Technical Description: Troubleshoot a Layer 2 issue and fix it with two configuration commands so the pings work successfully.




Challenge Instructions:

For this challenge, you need to start the topology called: “JAPAN -  Bridging with Virtual Switches”.


This is the connectivity state:


ping between H1 and H2 is OK

ping between H1 and irb.1 is OK

ping between H2 and irb.2 is OK

ping between H1 and irb.2 FAILs

ping between H2 and irb.1 FAILs

ping between irb.1 and irb.2 FAILs


First you need to find out why this is happening. You can use any firewall filters, as well as show and monitor commands, to discover the cause of the failed pings.


Then you need to fix the problem with:


-       Two set commands at just one device.




-       One set command at device A, and one set command at device B.


The configure/edit/commit commands are necessary but only the set commands are counted as the solution answer.


If you submit the right diagnostic and fix the issue, you solve the challenge!


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) (Only if you haven’t already submitted your address/shirt size on a previous submission)


Deadline to Respond: Tuesday, 24th of June 23:59:59 Pacific Daylight Time (PDT)

Timezone Converter

Some additional notes:

  • You can try to solve and submit answers for as many active challenges as you wish
  • 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.



The issue is that irb.1 and irb.2 both inherit their MAC address from the irb parent interface. So they get the same MAC, which results in a duplicate MAC address in the LAN. Although this is working as designed, this default behavior is not matching the functional requirements of the setup.

You can work around it as follows at the MX:


set interfaces irb unit 1 mac 02:00:00:00:00:01

set interfaces irb unit 2 mac 02:00:00:00:00:02


Julie Wider
Advocacy Manager
Twitter: @JNetCommunity & @jawider