Cisco Operating Systems

In this Cisco CCNA tutorial, you’ll learn about the different Operating Systems that run on Cisco’s different router and switch platforms. Scroll down for the video and also the text tutorials.


Cisco Operating Systems Video Tutorial

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Allan Gomez

Allan Gomez

I am CCNP certified and looking for CCIE certification soon. I took this course because it is more related to real work than other courses I have seen before.

Allan Gomez


A Short History of Cisco Operating Systems


I'll start by giving you a bit of history. Many people think of Cisco as being a routing and switching company, but they were just a purely routing company when they started off. When they started, IOS was the original Operating System that they used on routers, the same Operating System used today. It's gone through quite a few upgrades in the time since Cisco started back in 1984.


They were originally a routing company. To offer switches, that was through an acquisition. They bought Crescendo in 1993. The Catalyst switch product line came about because of that acquisition. The original Operating System on the Catalyst switches was CatOS, but that was deprecated quite a long time ago now.


A Short History of Cisco Operating Systems


Cisco firewalls evolved from another acquisition. That was the acquisition of Network Translation back in 1995. Cisco got their PIX firewall from that, which uses the Finesse Operating System. Now, both the Catalyst switches and the originally PIX firewalls, it's now the ASA firewall, were ported over to the IOS operating system over the following years.


A Short History of Cisco Operating Systems 1


Other Cisco Operating Systems


Cisco standardized on IOS for all of their network infrastructure devices. There are some other Operating Systems on some of the newer router and switch platforms. IOS runs on the majority of Cisco routers and switches, but some of the newer platforms do have these new Operating Systems.


Other Cisco Operating Systems


The Cisco Nexus and the MDS Data Centre switches run on NX-OS. On the high-end service provider routers, the NCS and the CRS, and the ASR9000 and XR12000 routers, they run on IOS-XR, and on the ASR1000 service provider routers, they run on IOS-XE.


So, you're maybe thinking, "Oh well, this is going to make things more difficult if there's all these different Operating Systems." But really, it doesn't, because all of the different Cisco Operating Systems are incredibly similar from the Command Line point of view.


Other Cisco Operating Systems 1


If you know a command in IOS, it's probably going to be exactly the same command in all of the different Operating Systems, as well. As far as administering and managing them, they're all nearly exactly the same.


You're maybe wondering, "If managing them is exactly the same, why are there the different Operating Systems?" The main reason, and where they're different, is under the hood. IOS has got a monolithic kernel, meaning that if one process running on the router crashes, it can crash the entire router.


The other newer Operating Systems have microkernels, and the processes run in separate, protected memory address space. So if one of the processes crashes, it shouldn't affect the running on the rest of the system. These other Operating Systems are mainly on the higher-end routers and switches, but they're still running IOS on the enterprise-grade routers and switches.


Now, don't think that IOS is a bad or an unreliable Operating System. It's been purpose-built by Cisco, the biggest networking company globally, to run on enterprise-grade routers and switches. So, it is very hardened. It's still very, very reliable.


Additional Resources


Cisco IOS Overview:

Cisco Internetwork Operating System (IOS):

Cisco IOS Explained with Features and Functions:


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Libby Teofilo

Text by Libby Teofilo, Technical Writer at

With a mission to spread network awareness through writing, Libby consistently immerses herself into the unrelenting process of knowledge acquisition and dissemination. If not engrossed in technology, you might see her with a book in one hand and a coffee in the other.