Difference Between Cisco NX-OS and Cisco IOS (With Table)

Cisco has been a pioneer in the industry of networking software since the company was first set in motion. It has developed and deployed several systems that combine cutting-edge technology with comprehensive hardware system support. Cisco NX-OS and Cisco IOS are two such systems out of the others that are widely acclaimed and used by many.

Cisco NX-OS vs Cisco IOS

The difference between Cisco NX-OS and Cisco IOS is that all the processes of Cisco NX-OS work in memory spaces that are independent of each other whereas Cisco IOS processes share a single memory space. This means that a malfunction in any process would not be much of a deal to Cisco NX-OS, but it would wreak havoc for other router processes in the case of Cisco IOS.

Cisco NX-OS is an operating system specifically designed for Nexus-series Ethernet switches and MDS-series Fibre Channel storage area network switches. It is an upgraded version of the Cisco SAN-OS operating system that was originally developed only for MDS switches. The system is built on the Linux kernel and has multiple high availability features.

Cisco IOS is another cisco operating system that was developed way before Cisco NX-OS. It can be looked at as a family of software that can be used on most Cisco System routers as well as current Cisco network switches. Its code base includes a cooperative multitasking kernel; however, it has several architectural limitations when compared to Cisco NX-OS.  

Comparison Table Between Cisco NX-OS and Cisco IOS

Parameters of ComparisonCisco NX-OSCisco IOS
DesignCisco NX-OS has several improvements in architecture over Cisco IOS.Cisco IOS has several architectural limitations as compared to Cisco NX-OS.  
Memory spaceIts processes work in protected and independent memory spaces.  Cisco IOS processes are shared over a single or pooled memory space.
FunctionsCisco NX-OS supports symmetric multiprocessing.Cisco IOS does not support symmetric multiprocessing.
DevelopmentCisco NX-OS is developed using the Python language code.Cisco IOS is developed using the C language code.
IP Address AssignmentThe subnet mask must be entered in slash notation.The subnet mask must be entered in dotted decimal notation.
VersionsCisco NX-OS is an upgraded version of Cisco SAN-OS.Cisco IOS is an older version of newer upgrades including Cisco IOS-XE and Cisco IOS-XR.

What is Cisco NX-OS?

Cisco NX-OS is a network operating system that offers excellent scalability and application availability. It evolved from the industry-proven system, Cisco SAN-OS that was made for MDS switches. Cisco NX-OS was upgraded to run on Nexus Ethernet switches as well. It was built with several IPv4 and IPv6 routing and multicast features. It provided comprehensive serviceability and security along with a unified data centre. The developers of the system used Python language code to build it.

Some key features on Cisco NX-OS include a virtual device context, virtual port channels, and continuous system operation. The system enables Layer 2 extension between distributed data centres over any kind of Layer 3 transport network. It provides a persistent storage service that is lightweight and efficient to maintain a runtime information state. This allows software components to checkpoint their internal state and allows a non-disruptive restart.

Cisco NX-OS even has a grace period that allows users to test, configure and operate a feature without having a license. This proves to be helpful when a user wants to test a feature before buying the operating system. The system also has a variety of platform support which includes Nexus 7000, Nexus 5000, Nexus 2000, Nexus 1000V, Nexus 4000, Cisco MDS 9000 as well as Cisco Unifies Computing System.

What is Cisco IOS?

Cisco IOS is an internetwork operating system that runs on several Cisco routers and switches. The main aim of the system is to facilitate data communication between two or more network nodes. It offers a plethora of features and services that enable a user to improve the performance and security of their network traffic. It was built using the C language code.

Some of the most notable features of Cisco IOS include authentication, encryption, policy enforcement, firewall capabilities, quality of service, intelligent routing, deep pocket inspection and even proxy capabilities. The system can also support call processing and unified data communication services. It enables preemptive multitasking which grants CPU time to high priority processes before it does to low priority processes. However, it has several limitations such as it does not support symmetric multiprocessing. Moreover, it can only run with shared memory space.

New versions of the system were launched to rectify these limitations. These new systems include Cisco IOS-XE and Cisco IOS-XR. Cisco IOS-XE runs on top of the Linux kernel. It shares code that is very similar to that of Cisco IOS-XR. However, the latter is based in QNX which is like a Unix real-time system. This enables it to support software-defined networking as well as embed the systems market.

Main Differences Between Cisco NX-OS and Cisco IOS

  1. Cisco NX-OS has several improvements in architecture over Cisco IOS whereas Cisco IOS has many limitations in operations.
  2. Cisco NX-OS processes use independent memory spaces to run whereas Cisco IOS processes are shared over a single memory space.
  3. Cisco NX-OS supports symmetric multiprocessing whereas Cisco IOS does not.
  4. Cisco NX-OS was built using the Python language code whereas Cisco IOS was built using C language code.
  5. Cisco NX-OS can enter the subnet in slash notation whereas Cisco IOS does so using dotted decimal notation.
  6. Cisco NX-OS is an upgrade to Cisco SAN-OS whereas Cisco IOS is an older version of Cisco IOS-XE and Cisco IOS-XR.


Cisco NX-OS and Cisco IOS are two network operating systems that are used by millions of people worldwide. Cisco NX-OS is a relatively new release with several improvements in design as well as a plethora of additional features. A major difference between them is that Cisco NX-OS can run its processes using independent memory spaces whereas Cisco IOS uses a pooled memory space for all its processes.

Moreover, while Cisco NX-OS enables a user to carry out symmetric multiprocessing, Cisco IOS does not. This means that Cisco NX-OS is much easier and more beneficial to use than Cisco IOS. However, Cisco IOS has upgrade versions including Cisco IOS-XE and Cisco IOS-XR that bridge the limitations. So, users now have a wide variety of options to choose from.


  1. https://link.springer.com/chapter/10.1007/978-1-4842-6672-4_19
  2. https://academiccommons.columbia.edu/doi/10.7916/D8TB1H7N
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