NX-OS is the operating system for Nexus switches. NX-OS was written from the ground up to be a modular, scalable, and resilient operating system for the next generation of data center switches.

NX-OS looks like IOS. It’s similar enough to make you feel comfortable but just different enough to be interesting and utterly frustrating until you get used to it. Many of the commands are the same, but the output of those commands is not what you’d expect if you’ve spent any time with IOS. Many of the commands are different entirely, and in some cases, contradict commands you may know from other Cisco devices.

There are web pages devoted to the many differences between IOS and NX-OS, and I could probably fill a book with such lists. Instead, I’ll concentrate on the common things that seem to trip people up when they first learn NX-OS. Some of these are my favorite “So you think you know Nexus?” questions during an interview, so if you get the job, send me a thank you.

NX-OS Versus IOS

Since NX-OS is Linux-based, it benefits from many of the features that Linux users have come to enjoy, not the least of which is stability and modularity. The first thing that usually frustrates people is the modularity of NX-OS. Nexus is designed to be efficient and, to that end, the operating system does not load unnecessary modules. For example, if you want to run OSPF, you’ll need to load the OSPF module. This is a departure from IOS, where everything is loaded regardless of need. As you might imagine, ...

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