To upgrade the IOS on your Cisco router, you have a couple of options. You can either upgrade via TFTP, or you can use the console.

On Ubuntu I used the atftpd software for my TFTP server:

Then to start it I ran:

Before doing anything first back up your configuration and original IOS from flash using the following commands:

copy nvram:startup-configuration tftp://x.x.x.x [follow the prompts confirming the server address source and destination file names]

copy flash:IOSNAME.ext tftp://x.x.x.x [follow the prompts confirming the server address source and destination file names] [if you dont know the filename of IOS in flash you can use the show flash command to view the contents of flash where the IOS should be listed]

If you load the wrong image of IOS, your router won’t work. Pay attention to the amount of RAM your system has, and how much the upgraded IOS needs.

You then need to delete the existing flash image:

delete flash:IOSNAME.ext [confirm at the prompts]

copy tftp://x.x.x.x/NEWIOS.ext flash [follow the prompts confirming the server address source and destination file names]

You will be asked if you want to erase the current image. Say yes.

Now copy your config:

Then reload the router to start in the new IOS:

If you’ve done everything correctly the router should reload and your on your way. If there is an issue with the IOS and the router does not come up correctly you will need to copy either the backup you made (I hope you did follow that step!) or the correct IOS onto the router using the rommon. This process I will leave for another post.