Cisco IOS Naming Convention Explained with Examples

This tutorial explains the naming convention used in the Cisco IOS image file. Learn how to get information about the features and functions of the IOS from the IOS image file name.

Cisco sells different flavors of the IOS software. A feature available in the one flavor of the IOS may or may not exist in the other flavor of the IOS. Besides this, how you configure a feature on a Cisco switch might be different from how you configure the same feature on a Cisco router.

But, it does not mean that all features are unique in each flavor of the IOS. For example, the way you access the IOS levels and the way you use many of the management commands are the same on all IOS flavors.

The features that are the same in all flavors are known as the base features while the features that are different in each flavor are known as the add-on features. All flavors of the IOS contain the same base features. Add-on features are flavor specific. Two IOS may contain some similar features or may contain completely different features.

Different router models usually use different hardware such as CPU and RAM. Because of the hardware difference, Cisco compiles different IOS images for different platforms and models. A low-end router or a fixed chassis router with limited physical interfaces needs different IOS software to support its interfaces than a high-end router or a modular chassis router that supports many different types of interfaces.

Cisco builds the IOS as a single image file. Instead of releasing bug fixes and updates separately, Cisco compiles them into the IOS image file and releases a new IOS file incorporating those changes. It means, to add a bug fix, to move to a new release, or to move to a new version, you have to download and install a whole new IOS image file.

In short, if you have Cisco routers or switches that use IOS images, you have to install and manage a lot of IOS image files. However, if you know the naming convention that Cisco uses to compile its IOS image files, this process is not difficult.

Cisco IOS naming convention

Cisco assigns a unique name to each IOS image file. This name provides the following information: -

  • The platform for which the IOS compiled.
  • Features that this IOS will provide.
  • Type of the compression that was used to compile the IOS.
  • The location from where the IOS will run.
  • Version and Release numbers.

To release the major updates and minor bug fixes, Cisco uses the terms: version and release, respectively.

Let's take an example to understand this naming convention in more detail. Access the CLI prompt of your router. If you don't have a real Cisco router, you can use the Packet Tracer.

Packet Tracer is a network simulator software. It allows you to practice with essential Cisco devices in a simulated environment. You can download the latest version of the Packet Tracer from the following web page.

Download the Packet Tracer for Windows and Linux

Access the privileged-exec mode and run the "show version" command. The output of this command, along with other information, contains the name of the IOS file that is currently running on the router.

The following image shows the output of this command on the Packet Tracer.

show version command

A router stores IOS files into the flash memory. You can also use the "show flash" command to view all available IOS files.

The following image shows the output of this command.

show flash command

As we can see in the output of both commands, the name of the IOS file is the following.


Let's understand this name word-by-word.


Cisco creates a separate IOS for each series of routers. Because of this, each IOS works only on the router belonging to that series. The first term indicates the series of routers for which the IOS file is compiled. The word 'c1841' indicates that this IOS file is compiled for the 1841 series routers.


Besides the base features, each IOS contains some special add-on features. The next term represents these features. The word 'advipservices' indicates that this IOS contains special security features for advanced IP services. The trailing 'k9' indicates that this IOS supports encryption.

The following table lists a few feature-set codes and their meanings.

Feature-set code Description
J Enterprise
JS Enterprise Plus
JK8S Enterprise Plus with IPSec


The next term indicates whether the compression was used to pack the IOS file or not. The word 'mz' indicates that the IOS file is compressed. If the IOS file is compressed, it must be decompressed before use.

The following table lists some common types of compression that are used to compress the IOS file.

Code Compression
Z The image is compressed in the ZIP format.
X The image is compressed in the MZIP format.
W The image is compressed in the STAC format.


If the IOS runs from the non-standard location, the next term indicates that location. The following table lists some common locations and their codes.

Code Memory Location
F The image will run from the flash.
M The image will run from the Random Access Memory (RAM).
R The image will run from the Read-Only Memory (ROM).
L The image will be relocated at the runtime.

The next term shows the version and the release numbers. The version and the release numbers of this IOS file are 124-6 and T7, respectively.


The last term 'bin' indicates that this is a binary image.

That's all for this part. In the next part of this tutorial, we will understand the IOS modes and how to access them. If you like this tutorial, don't forget to share it with friends through your favorite social platform.

ComputerNetworkingNotes CCNA Study Guide Cisco IOS Naming Convention Explained with Examples