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Install Cisco IOS on Switches Using XModem

There comes a point in every engineer’s life where you find yourself having to load software onto a Cisco switch. More often than not we find ourselves doing this in 2019 to Cisco switches that are now used for lobbying or even on Cisco switches that are still used in a production environment.

The problem I’ve seen is that we (as engineers) have much to remember, we often forget the little things or better yet, we lose the skills we don’t use but fear not, this article hopes to bring back at least one of those skills!
Whether a switch is corrupted with the wrong image or you’ve simply purchased a switch that doesn’t have a software image loaded, there isn’t a way to provide IP connectivity in order to load a new image so we have to do things a slightly different way…and that way is XMODEM.
Now I’m not going to jump into the details of this ancient protocol because no doubt if you’re an engineer you’ll know all about it right 😉 but I will provide a link to more details on xmodem for those avid readers Read More Here.
Now let’s take a look at how we can transfer a Cisco IOS image to a switch using xmodem. The following demonstration was performed on a Cisco 3560 switch.
What you need to get started
  1. Console Cable
  2. Direct Access to the switch
  3. Windows machine to run the Tera Term application
  4. Compatible Cisco IOS image for your device
  5. Time
  1. Connect your console cable to the Windows machine and console port of the Cisco switch. This needs to be direct and not via any terminal servers, I tried this and it didn’t work when changing the baud.
  2. Open Tera Term and connect to the serial port of the switch. With the switch powered on you should be presented with the following syntax:
  1. Initialize your switch’s flash by entering the following command. Some switches will already have this enabled and you will be notified of the result once you’ve pressed enter.
  1. Check that you don’t have any images already installed in your flash and verify your storage.
dir flash:
  1. On the switch, set the baud rate (speed). Follow the steps to the end because you will be required to change this back when the image has been successfully transferred.
set BAUD 115200
  1. Now change the baud rate on Tera Term to match that of the switch. Setup > Serial Port > 115200 It might seem as though your terminal session has frozen but this isn’t the case, press enter a few times and it should come back.
  2. Enter the following command to start the image transfer.
copy xmodem: flash:.bin
  1. Staying on Tera Term, select the file to transfer navigate to File > Transfer > XMODEM > Send and select the image file. The file should begin transferring to the switch. The waiting game begins! It can take a minimum of 30 minutes depending on the size of the image file.
  2. Once the image has been transferred, change the BAUD rate back on the switch and then Tera Term using the same method already mentioned above.
  3. Boot into your new image.
boot flash:.bin
And that’s all there is to it!
Thank you for reading and I hope that you’ve found this article useful.


Kelvin is a Cyber Security professional with years and experience working with organisations in different verticals, both large and small. He enjoys contributing to the Network Wizkid knowledge base and he also creates technical content. Kelvin enjoys learning new things and often does this by working on achieving new technical certifications. He holds many professional certifications and academically, he has achieved a Bachelors and Master's degree in both Computer Networks and Cyber Security.

This Post Has One Comment

  1. Danny

    The piece I was looking for.

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