Cisco IOS Naming Conventions (12.4)

Just had a really interesting read(!) of the Cisco IOS naming convention whitepaper, so to save other peoples sanity I thought I would share my notes :)

The non 'T' train of 12.4 is there to provide the most stable releases. Maintenance deployment (MD) releases of 12.4 (non 'T') are the MD of the 12.3T train. This implies these are the most stable releases available. New releases constitute mostly software fixes

The 'T' train of 12.4 is there to provide new releases with the latest feature and hardware support. Early Deployment (ED) releases of 12.4T introduce new functionality that is not available in the 12.4 train. They also receive software fixes. There will be the occasional MD release of 12.4T

The release number (digits that follow 12.4, e.g. 12.4.xx) are unique across both 12.4 and 12.4T, e.g. 12.4.10a -> 12.4.11T1 -> 12.4.12a -> 12.4.12b -> 12.4.13T1

The rebuild letter follows the release number in the 12.4 train, e.g. 12.4.10b denotes the second rebuild of 12.4.10

The rebuild number follows the release number in the 12.4T train, e.g. 12.4.13T4 denotes the 4th rebuild of 12.4.13T4

In 12.4, 'Releases' include mostly software fixes, and occasionally minimal new feature support and minimal additional hardware support

In 12.4T, 'Releases' include software fixes, new features and additional hardware support

The rebuild designation (a letter for 12.4 and a number for 12.4T) shows that there has been a rebuild of the software to improve stability. The criteria on what changes are made in a rebuild are very strict.

In summary, choose a 12.4 (MD) with the highest release and rebuild letter for the most stable release available and choose 12.4T (ED) with the highest release and rebuild number for the IOS with the latest features and hardware support.

For full details of the IOS naming conventions, see the following link:

http://www.cisco.com/web/about/security/intelligence/ios-ref.html