Cisco IOS Naming Convention Explained with Examples

Cisco IOS (Internetwork Operating System) is a proprietary operating system. It allows you to control and manage the Cisco device on which it runs. Initially, Cisco developed it for routers. Later, it implemented it on other supported devices such as switches and firewalls.

Cisco makes many types of routers and switches. Different models use different hardware components, such as CPU, RAM, and physical interfaces. Low-end routers or fixed chassis routers have limited physical interfaces. High-end routers or modular chassis routers have multiple physical interfaces.

Because of hardware differences, Cisco compiles different IOS variants for each platform and model. Each IOS variant includes standard features for general functions, as well as model- or product-specific features. Two IOS variants may contain similar features or completely different features. The features that are common to all variants are known as base features. The features that differ across variants are known as add-on features.

Cisco builds the IOS as a single image file. Instead of releasing bug fixes and updates separately, Cisco compiles them into a new IOS image file and releases it. Because of this approach, if you want to update an existing IOS, you have to download and install the updated IOS image file.

When selecting or updating an IOS image file, it is essential to choose the correct one with the proper feature set and version. To make this process easier, Cisco uses a special naming convention for IOS image files. The IOS naming convention provides the following information:-

• The platform, model, or device on which you can use it.
• Features that this IOS will provide.
• The compression type used to compile the IOS.
• The location from where the IOS will run.
• Version and Release numbers.

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

Example

There are many ways to view the name of the running IOS's name. The most straightforward method is using the show version command. The output of this command displays the name of the running IOS image file. It is a Privilege Exec mode command.

A router stores IOS image files in the flash memory. You can also use the show flash command to view all available IOS files on the router.

The name of the IOS image file in the above output is:

c1841-advipservicesk9-mz.124-6.T1.bin

c1841

Cisco creates a separate IOS for each router series. Each IOS works only on routers of that series. The first term indicates the series of routers for which this IOS image file is compatible. The word 'c1841' suggests that this IOS file is for the 1841 series routers.

advipservicesk9

In addition to base features, each IOS contains some special add-on features. The following term represents these features. The word 'advipservices' indicates that this IOS contains special security features for advanced IP services. The trailing 'k9' suggests that this IOS supports encryption. The following table lists feature-set codes and their meanings.

mz

The following term indicates the compression type used for this file. The boot process automatically decompresses the compressed IOS image before loading it into RAM. The following table lists common compression types used to compress the IOS file.

Location

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

.bin

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

Conclusion

Understanding the Cisco IOS naming convention is crucial when selecting or updating IOS image files. This convention provides vital information regarding the compatibility of the IOS with specific device models, the features included, the file compression type, and the versioning details. By grasping the meaning behind each component of the IOS filename, you can deploy the correct IOS variant that meets your operational requirements.