Recover from IOS Armageddon

Categories: Networking, Tips


Ok, maybe it’s not that extreme, but losing power to a Cisco router or switch, while performing an IOS upgrade, after you’ve deleted your existing IOS can be a headache.  While not a disaster, you can plan on spending about an extra 45 minutes or so to recover.  Here’s the lowdown:


You’ll need to upload a new IOS image using the Xmodem or Ymodem protocol, which is way slower than TFTP or other methods (about 50 times slower!).

What You’ll Need

  • Cisco console cable
  • Terminal emulator w/Xmodem or Ymodem support
  • IOS image of choice

Step 1

Configure the router for the fastest connection possible (115kbps) using the “confreg” command, as shown here.  Also, configure the speed of the serial port on the computer that you are connecting to the device with to the same speed.


Step 2

Upload image using a terminal emulator with support for Xmodem or Ymodem.  If you’re using Windows XP, you can use hyperterminal in combination with telnet.  I prefer to use “SecureCRT“, but if anyone has any other recommendations, don’t be shy to comment.  Be prepared for this process to take up to an hour for an 15 MB IOS image.  If you’re looking at a couple of hours for the same file size, most likely you don’t have your transfer or serial port speed set correctly (see step 1).

Step 3

Reload router using uploaded IOS image.  Don’t forget to change the speed settings on the network device and computer back to the default (9600kbps).