10 October 2008

Cisco IOS Naming Convention and Features

When you decided to buy Cisco devices for a home lab, it is very important to ask the reseller about the Cisco IOS image the devices are using.

This is something that most newbies are forgetting about when buying used Cisco devices for the first time.

This should be no problem if you buy Cisco kit/home lab package, since the reseller will optimize the requirements for you, including the IOS version.

Now what exactly is the differences in Cisco IOS package names and the features they have. To list every one of them here is a very tiring work since there might be hundreds if not thousands of IOS packages with different versions and features.

What I can tell you is that the above image shows the naming convention of Cisco IOS images. You will oftenly see the above format used in the naming of IOS image.


The first part is quite self explanatory, hardware is the hardware supported by the IOS.


This is where you can find out the features supported by the IOS. This is the new naming convention of Cisco IOS, some older version still use letters to describe the features. The "Legacy naming convention" can be quite confusing, so it's good they decided to change the naming convention.

Cisco distributes IOS packages according their features, take a look at the following diagram:

The higher the features set, the more features it has. You can check the features of Cisco IOS image with the tool provided by Cisco.
Access the tool at cisco site, and you can search by features, IOS image name, platform, product code, and you can even compare features between images. Great tool you should try.

For the legacy naming convention, you can find it formated as yyyy, where the y can be replaced by the following letters:

  • b - For Apple talk support
  • c - For CommServer lite (CiscoPro)
  • g - For ISDN subset (SNMP, IP, Bridging, ISDN, PPP, IPX, and AppleTalk)
  • i - For IP sebset (SNMP, IP, Bridging, WAN, Remote Node, and Terminal Services)
  • n - For IPX support
  • q - For asynchronous support
  • t - For Telco return (12.0)
  • y - For reduced IP (SNMP, IP RIP/IGRP/EIGRP, Bridging, ISDN, and PPP)
  • (c1003 or c1004)
  • z - For managed modems
  • 40 - For 40 bit encryption
  • 50 - For 50 bit encryption


This section tells you from which memory location the IOS and what format of compression it uses. Check the following for the formats:

  • f - flash
  • m - RAM
  • r - ROM
  • l - the image will be relocated at run time

And these are the compression types:

  • z - zip compression
  • x - mzip compression
  • w - “STAC” compression


These shows the release version number of the IOS image.


The last part shows whether the image is T Release (new feature release identifier), S (individual release), or XR (modular packages).

For further reference you can see the complete list here and here.

I've made a mistake when I first bought my router, I didn't ask about the IOS version of the router so I ended up with a very basic IOS version not having even DHCP server feature.
You don't want to make same mistake, so get familiar with Cisco IOS naming convention.

If you already bought it, check the features supported by the image with the Cisco tool I told you above.

You need also consider the amount of DRAM of the device. The higher the version and features of an IOS, the more DRAM you need.