This tutorial explains the naming convention used in the Cisco IOS image file. Learn how to read the IOS file name to get information about the features and functions of the IOS.
Cisco IOS (Internetwork Operating System) is a proprietary operating system. It allows you to control and manage the router or the switch on which it is running. Originally, Cisco developed it for routers, but over the last few years, Cisco has been porting it to its other platforms, including the Catalyst switches.
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 the hardware difference, Cisco compiles different IOS variants for every platform and model. Each IOS variant includes similar features for general functions and some model-specific features for the model or the product-specific requirements.
Two IOS variants may contain similar features or completely different features. The features that are the same in all variants are known as the base features. The features that are different in each variant are known as the 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 the approach, if you want to update an existing IOS, you have to download and install the updated IOS image file.
When selecting or updating a Cisco IOS, it is important to choose the proper IOS image file with the correct feature set and version. To make this process easier, Cisco uses a special naming convention for IOS image files.
In this convention, Cisco provides information about things: -
- The platform for which the IOS was 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.
Access the CLI prompt of the router and run the "show version" command in privileged-exec mode. The output of this command includes the name of the running IOS image file.
The following image shows the output of this command.
A router stores IOS files in the flash memory. You can also use the "show flash" command to view all available IOS files on the router.
The following image shows the output of this command.
As we can see in the above output, the name of the IOS image file is the following.
c1841-advipservicesk9-mz.124-6.T7.bin
Let's understand this name word-by-word.
c1841
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.
advipservicesk9
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 |
| I | IP |
| IS | IP PLUS |
| J | Enterprise |
| JS | Enterprise Plus |
| JK8S | Enterprise Plus with IPSec |
mz
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. |
Location
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. |
124-6.T7
The next term shows the version and release numbers. The version and the release numbers of this IOS file are 124-6 and T7, respectively.
.bin
The last term 'bin' indicates that this is a binary image.
That's all for this tutorial. In this tutorial, we discussed the Cisco IOS image file naming convention and learned the meanings of some important terms used in the naming convention.