Demystifying Cisco Config Register Bits

Ever accidentally set your config register to a random value that isn’t in the Cisco documentation? No? Neither have I, but one day I encountered someone on #cisco that had. So I did my best to help him, and was able to decode his settings and get him back into the CLI.

First things first. Lets hope you remember the value you entered, or else you’re going to be trying every bit rate.. If you do, convert it to decimal then binary, or straight to binary if you’re a badass. For example lets use 0x2121. Cisco has no reference of this in their documentation. Now that you can’t get into your router at the typical 9600 8,N,1…

1. Convert 0x2121 to decimal………….. 8481
2. Convert 8481 to binary…………………. 10000100100001
3. Insert this number into the table below… Top->Bottom; Right->Left
            I’ve filled in the values on the far left column.

4. You’ll notice our values for the console line speed rows exactly match that of the 19200 column.

Thats it ! Fire up your console at 19,200 baud and you’ll be set…

I hope this helps someone out, if you do have any questions, please feel free to ask.