ASA understanding version numbers
ASA devices run ASA software that are defined by specific version numbers. Version numbers appear in the format similar to the following:
The first number is the Major Release (8), then the Minor Release (4) and finally the Maintenance Release (1). Some images also contain an additional number in brackets which indicates that this particular version is an interim version.
An interim version is created and published by Cisco as an intermediate image for ASA devices. This is most often because of urgent bug fixes what have been discovered since the main image has released, and are quickly released to resolve them.
In the show version output, we will see the version information displayed like so:
Cisco Adaptive Security Appliance Software Version 8.4.1(11) Compiled on Tue 14-Dec-10 12:00 by builders System image file is "disk0:/asa841-11-k8.bin"
When we look at the system image file, it looks like this:
asa841-k8.bin or asa841-11-k8.bin
The name of the system image file indicates this same version number, but without the periods "." and the brackets"()".