Cisco IOS Naming Conventions

As I started building this lab, I realized that I had to find a refresher course on the IOS naming conventions. They have gone through a number of revisions through the years, but here is a guide that should help most of you building CCNA/CCNP labs.

Lets take c3640-jk9s-mz.124-16.bin for example.

The first thing we see is a platform designator. c3640 tells us that the IOS is for a 3640 router. See, I told you this was easy.

After that you see a series of alphanumeric characters, these designate feature sets included in the image.

“c”       Remote Access Server
“i”       designates IP feature set
“j”       designates the Enterprise feature set (all protocols)
“s”       designates a PLUS feature set (extra queuing, manipulation or translations)
“s2″     Voice IP to IP Voice Gateway (26xx/36xx/37xx only)
“s3”     “Basic” (limited IP routing, for limited-memory 26xx, 36xx)
“s4” “Basic” without switching
“s5” “Basic” without HD analog/AIM/Voice
“56i”   designates 56-bit IPSec DES encryption
“o”      designates the Firewall
“o3”      designates the Firewall/IDS
“k2”      designates  included encryption (having trouble finding exact info on these.. )
“k8”      designates the DES encryption
“k9”      designates the 3DES IPSec encryption (168-bit)

The next part tells you where the image runs from, most end in ‘mz’, ‘m’ meaning it runs from memory (not flash), and ‘z’ tell us that it is zip compressed.

The third part we have is the actual IOS version number itself, for example:
“124-16”     indicates IOS 12.4 subrelease 16