Tuesday, December 31, 2013

Notes on resetting and connecting to a Juniper router

This is another of those notes I wrote primarily to myself. It has to do with a Juniper appliance, namely a SSG5, which runs ScreenOS. I had some issues with its configuration, as I screwed up and could not log into it from either the network port or console. It felt it was high time to wipe and reconfigure the little guy.

Juniper has some notes on doing the deed, but there are a few things I would like to mention:

  1. You really want to do this resetting dance while the outer is not connected to any network. You know, just in case someone does recognize a router in default mode and have a field day.

  2. Having a good DB-9 RS-232-to-usb cable makes all the difference. I would strongly recommend one using the FTDI Chipset. Without that you might end up rather frustrated. There are a lot of companies, FTDI itself included, making such cables. For the lazy and curious amongst you, the one I personally own is the Sabrent USB2-to-RS-232 cable, model CB-FTDI.

  3. Find something convenient to reach the button, and a way to hold the router in place. When I first tried it, I used a trusty paperclip to press the reset button on the back. The brilliant (at the time) idea but was that if I could hold both the router and paper clip with one hand, I then would be able to see the lights on the front of the router. It would work fine if I was holding router with its back towards me. In real life, with me trying to see its blinking light, the paper clip kept sliding off the reset button, lodging itself between the button and the board (I think; I haven't opened it). What worked for me was a mechanical pencil. Its (7mm) tip was thick enough to just fit the reset button hole and its body felt just right to hold from the back.

  4. Resetting the router turned to be close enough to what was described in Juniper notes on resetting this router, but not exactly. Specifically,

    1. When you press the reset button, hold it until it starts blinking orange. Until that happens, just keep on pressing the button.
    2. Once it starts bliking orange, let it go. It will go green.
    3. Wait 2-4 seconds and then press the reset button again. The exact time might need some practice; in my case it was more like 3s. You know you got it right because once you press the button the LED will start blinking red.
    4. Now (led blinking red) release the router reset button and let it do the boot process continue.
  5. Know the serial port settings: 9600 8N1, the same as many Cisco devices. How you will configure that and connect to router is up to you. I have used screen (Linux/OSX/Others), minicom (Linux), and tip (Solaris), but I do know Windows also has a terminal program (HyperTerminal?) that comes with it that will work just fine. Or putty. I like putty.
  6. Running a packet acquisition package in a router LAN port is quite useful, specially if you have setup router to use a different network/IP than the default. When I first did the reset, the USB-to-serial cable I had was not working with the router's serial port.

    While I was waiting for the CB-FTDI cable mentioned above, I used wireshark (I was feeling lazy; nothign stopping you to use something fancier you already had... or write your own routine) to look at the traffic at the lan. Before it was reset, the router would keep sending arp requests in broadcast. And that would tell me which network it was configured to use, which was not the default ( Now, as soon as I successsfully reset the router, traffic went quiet during bootup but then I started seeing traffic from As the only device in that network -- my ethernet cable was just connected to the laptop doing the packet capture -- that told me the reset was successful. Then, I turned wireshark off, set some ip in the same network for the ethernet port connected to router, and checked if the web interface mentioned in the manual, and which I have never used, was there. Nope, all ports were closed. So I just had to wait for USP to deliver the USB-to-serial cable.

  7. As the manual and the link states, the default login and password are both nnetscreen.