One of my favorite interview questions to ask network engineering candidates is “How many different ways can you describe to determine the serial number of a Cisco router?”
…and I got to thinking: How many ways do I know how to obtain the serial number of a Cisco router? So I began writing them down and here is what I came up with:
- Locate the serial number tag on the router chassis.
- The serial number is displayed in the banner during boot.
- “show version” command. (Look for “Processor board ID”)
- “show inventory” command. (Look for “Hw Serial#” or “SN:”)
- “show diag” command. (Look for “Chassis Serial Number”)
- “show hardware” command. (Look for “Processor board ID”)
- “show tech-support” command. (Displayed MANY times)
- “show run | s snmp-server chassis-id” command. (Must have been manually set)
I really wanted to make this “10 Ways To Find The Serial Number of Your Cisco Router” but I honestly couldn’t think of two more ways to grab the serial number of a router. I’m certain there are probably a couple more obscure ways to do this, but I haven’t bothered scouring the IOS commands in search of alternative means of determining a serial number. I thought there was a way to manually specify the serial number in the configuration (not utilizing the snmp-server command), but I couldn’t readily put my finger on it.
Anyway, I’ve used this question during interviews for many years and continue to do so because I believe it gives me a good insight into the individual we’re considering. I expect the obvious answer (#1) and any combination of the rest help me to determine how familiar (hands-on experience) a candidate is with Cisco routers. Some times when I push a candidate for more information, I receive creative responses that even while not correct reveal a person’s problem-solving mindset. And that’s what I’m most interested in. Plus, it’s fun to watch them squirm. 🙂
I’d love to hear from you, especially if you can share (valid) ways to determine the serial number of a Cisco router beyond what I’ve enumerated above.