Data Center Basics: Similarities Between IOS and NX-OS

As an engineering professional, I’ve been using the Cisco Internetwork Operating System (IOS) since I entered the industry in 1998. At that time the commonly used version number was 11.2, with plenty of new features that made it more desirable and useful than the previous releases. Naturally, IOS formed the bedrock of Cisco networking technologies and powered all equipment since the beginning. Along the way however, some additional platforms, usually through the process of acquisition by Cisco, introduced additional operating systems. For example, for a number of years Cisco switches ran either IOS, Catalyst OS (CAT OS), or a hybrid of both. In addition, I personally work on the Content Services Switch 11500 Series, which also ran a separate operating system, which was certainly not IOS but maintained some similarities, leading me to describe it as “IOS-Like.”  

With the introduction of the Nexus Series of Data Center switches, Cisco created the Nexus Operating system, commonly abbreviated NX-OS. While certainly not exhaustive, the Nexus switch line includes the 7000, 5000, 2000 (fabric extenders), and the 1000V Virtual Switch. While these devices were intended for use in the Data Center, models such as the venerable Catalyst 6500 series have been increasingly displaced by corresponding Nexus models in the core. I have designed and worked to install these very solutions for Fortune 500 customers during my tenure as an engineer.  

To those new to NX-OS, a natural and legitimate question centers around the similarities and differences between the more familiar IOS and the newer NX-OS; this two-part discussion is designed to answer that very inquiry.


Exec Mode/Prompts

Both IOS and NX-OS have a similar “look and feel” when it comes to the command line interface

(CLI) with an almost identical appearance in what is usually referred to as privileged mode. The prompt (the string displayed when you log into the device) is also similar, using the format <hostname>#, with the # character indicating privileged mode. In the CLI the shortcuts are mostly the same, such as: 

Tab: Completes partial commands
Ctrl+A: Places cursor at the beginning of the line
Ctrl+E: Places cursor at the end of the line
Ctrl+W: Erases the last word currently on the line
Ctrl+U: Erases the current line
Ctrl+Z: Exit configuration mode
Backspace: Erases one character to the left
Up arrow: Displays back through the last commands in the history
Down arrow: Displays forward through the last commands in the history
?: Displays context-sensitive help

Configuration Files

Another similarity is the use of system configuration files, which use the same naming conventions and occupy similar places in the life of the device:  


  • Stored in non-volatile random access memory/NVRAM
  • Loaded into memory during the boot process
  • Not directly modified while making configuration changes in real-time 


  • Stored in RAM/DRAM after loaded by the boot process
  • Contains current valid configuration for the device
  • Modified while making configuration changes in real time 

CON/VTY Configuration 

Configuration of the access to each type of device using console and virtual terminal lines has almost the identical syntax, making the processes very familiar. Similar commands are: 

  • Line con
  • Line vty  

Show/Debug Commands

Many traditional show and debug commands are remarkably similar across both classes of devices, including the following (not exhaustive): 

show startup-config: Displays the startip configuration stored in NVRAM
show running-config: Displays the running configuration stored in RAM
show vlan: Displays existing Virtual LANs configured on the device
show interface: Displays the operational state of interfaces
show mac address-table: Displays the switching table(on switches)
show ip route: Displays the ip routing table
show processes cpu: Displays the current CPU usage and processes
show version: Displays the current hardware/software on the device
show cdp neighbors: Displays other neighboring Cisco devices running CDP

Configuration Commands

Much of the same syntax for configuration of common features is similarly configured across both platforms, and while not a complete treatment, here are some common ones: 

configure interface: Configure interface options
vlan: Create Virtual LANs
ip route: Create static/default routes on the device
route-map: Create entries for a route-map
clock: Set clock and/or timezone settings
ntp server: Specify time-source settings
spanning-tree vlan root: Set the current device as the root
switchport mode access: Set a switch port for access mode (single vlan)
switchport mode trunk: Set a switch port to trunking mode
username: Configure user credentials locally on the device

Hopefully, this gives you an overview of the similarities of these two operating systems, and builds a sense of comfort with the familiar aspects.  Next time, we will continue the analysis, this time concentrating on some of the differences between them.

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