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Supervisor Engine 720 crashes while it tries to bootup in a Cisco Catalyst 6500 Series switch running Cisco IOS software


Core issue

When this issue occurs, the Cisco IOS  image could be corrupt or the Supervisor Engine crash could be due to Cisco bug ID CSCee63221.

Another reason can be due to the incorrect config-register setting on both the Route Processor (RP) and the Switch Processor (SP). The configuration register boot field determines whether or not the switch loads an operating system image, and if so, where it obtains this system image. The config-register can get out of sync for a variety of reasons, for example, changes in ROMMON, a CatOS to Cisco IOS upgrade, and so forth.

If any one of the two (RP or SP) is set wrong, it causes communication failure between the RP and SP hence device crashes. Once you set the config-register to the proper setting, the RP and SP synchronize, which allows the device to boot properly.


If the Cisco IOS image is corrupt, complete these steps:

  1. Download a fresh copy of the Cisco IOS image from Cisco Downloads.  
  2. Remove any previously entered boot statements.  
  3. Re-enter the boot statement and specify the config-register value.

This is an example: 

sw#configure terminal

sw(config)#boot system flash disk0:[filename]

sw(config)#config-register 0x2102


If the Supervisor Engine crashes due to Cisco bug ID CSCee63221, upgrade the code to Cisco IOS Software Release 12.2(17D)SXB5. This release has a fix for this bug.

Refer to the Configuring the Software Configuration Register section of Configuring the Switch for the First Time for more information.

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