Understanding Cisco Access Point IOS Images

From Aaron Leonard - Cisco

All Cisco Aironet wireless access points and bridges currently being shipped run IOS.  The only exception is the OEAP602.  (Some older Cisco access points did not run IOS, such as the Aironet 340 which ran only VxWorks, and the 1000 series lightweight APs.)

Access Point IOS is distributed as a tar file.  These tar files can be downloaded from cisco.com SDS; lightweight IOS images (k9w8) are also bundled in the WLC software images (.aes.)

The IOS image names include the following components:

platform-featureset-tar.version.tar

• platform- the access point hardware model or family supported by the image       
  • examples: c1250; ap3g1 - 3500/1260; ap801- AP embedded in 881W; c1520 - 1520/1550
• featureset- the set of software features supported by the image - one of:      
  • k9w7 - autonomous IOS
  • k9w8 - full lightweight IOS (this is what is bundled in the WLC .aes image, and is factory installed on "mesh" APs)
  • rcvk9w8 - lightweight recovery image - this is factory installed on lightweight APs, unless a "mesh" image is specified; it lacks radio firmware
• version- the IOS version       
  • There is a 1:1 mapping between the lightweight IOS software version (such as 12.4(23c)JA) and the CUWN version (such as 7.0.98.0)  
    • see the Wireless Solutions Software Compatibility Matrix on CCO

Example: c1240-k9w7-tar.124-25d.JA1.tar

• Platform: c1240: 1240 series AP
• Featureset: k9w7: autonomous IOS
• Version: 124-25d.JA1: 12.4(25d)JA1
  

As AP IOS is always distributed as a tar file, the AP cannot directly execute such a file (thus, if you were to copy c1240-k9w7-tar.124-25d.JA1.tar directly onto AP flash, and then try to boot it, this could not work.)  The tar file contains, in addition to the IOS image proper, the radio firmware files, the HTML GUI files (if present), and various other files.  The AP IOS tar file must be unbundled into AP flash using the archive exec command (this is done in an automated fashion when a lightweight AP is upgraded after joining a WLC.)  After unbundling, the IOS image itself be in a file called flash:/platform-featureset-mx.version/platform-featureset-mx.version - for example, flash:/c1240-k9w7-mx.124-25d.JA1/c1240-k9w7-mx.124-25d.JA1.  The AP is configured to boot this image if the bootloader BOOT environmental variable is set accordingly.