Verifying IOS should be a no-brainer, but I admit it’s something I forget to do sometimes.
Here’s my process.
First download the IOS image from Cisco. Cisco provides the MD5 hash (hover over the image name to see it. Make note of it or copy and paste into the spreadsheet attached to this post.
Once downloaded I verify the hash again. There are a bunch of apps out there, I use HashMyFile. Here’s a shot of the verification of the downloaded file.
The hash matches so we’re good on the download. Next we put the IOS on the device. I prefer to use SCP or FTP. TCP based transfers are more reliable that UDP (TFTP uses UDP if you didn’t know). Once we get the image on the device let’s hash it again to make sure it was copied over correctly.
Copy that into the spreadsheet or verify against your notes. If they match we can set our boot statement and reload. If it does not match delete the file and try the upload again. Since we verified the downloaded file we know the problem is in the transfer.
I created a spreadsheet that saves me some time. You copy-n-paste the hash from Cisco or your local hash and then copy the hash from the router verify command. If they match the cell turns green and I know it’s good. If the cell is red they don’t match. It’s just a quick visual check. Here’s a screenshot of what each one looks like.
If you’re interested in the excel file you can download it here