TIP: How To Do MD5 and SHA1 File Checksum Validation
It’s always a good idea to calculate an MD5 or SHA1 file checksum to validate file integrity after download or transfer, especially when dealing with firmware binaries. While most modern systems are smart enough to validate images before attempting an installation, not all are so wise, and I’m sure I’m not the only one to have seen a device bricked (or stuck in ROMMON or a similar bootloader or equivalent) after a bad image was uploaded.

Here’s a quick reference guide to creating file checksums on Macos (OSX), Windows and Linux.
File Checksum Validation
There are various ways to check md5/sha1 checksums depending on your preferred platform. Vendors tend to publish the MD5 or SHA1 checksums (or both) for downloadable files, so it’s silly not to do checksum validation and confirm that the file has downloaded completely and uncorrupted. I try to validate after each time I transfer a file so that I don’t waste time sending a corrupted file on to the next hop. For example:
- Download image file from Cisco’s website
- — View the checksum and compare
- SCP the file to a target jump server
- — View the checksum and compare
- SCP the file to the end device
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