nd 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 NX-OS 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 imag- line, loading all the code for OSPF, BGP, and a myriad of other features you might not need can be wasteful. If you've ever compiled your own Linux kernel for speed and reliability, you'll recognize the benefits of this methodology. Modules of code are called features in NX-OS. To load a module, use the feature command. To see which features are available, use the show feature command. Here is a list of features from a Nexus 5000: NX-5K-1# sho feature Feature Name Instance State tacacs disabled enabled interface-vlan enabled private-vlan disabled disabled enabled disabled enabled As I was working on this section, I typed a command in the wrong config mode. The Nexus is smart enough to know how stupid I am, and further felt the need to comment as it showed me the answer I was really looking for. Here, I tried to use the feature command whil