2960 switch went to a booting loop due to bug CSCvf46629 when doing an upgrade from 15.2(2)E7 from 15.0(2)SE7. That is when VTP mode set as client on the switch, switch will go into reloadloop when trying to upgrade switch to 12.2.2E7.
To recover the switch we need to move the switch to old IOS then boot switch up, then change the vtp mode to transparent.
If you have old IOS image in the flash, then just need to boot switch during pressing “mode” button until switch prompt shows up, then doing flash_init and boot from the old image.
In my case the old IOS image was removed during new image installation, so I have to download the old IOS image to the switch via console port.
Below is the steps to follow:
-Set BAUD 115200
-copy xmodem: flash:OLD_IOS_image
Transfer the IOS file from computer to the switch with Serial tool in Mac or Hyperterminal in window. Once old IOS is copied:
Once switch boots up in old IOS customer needs to boot up the switch and change the vtp mode, Then do the upgrade from 15.2(2)E7 from 15.0(2)SE7Then change the vtp mode back.
To set Baud as 115200 is because using the default Baud rate 9600 for file transfering will take 3-4 hours to download the ios image to the switch. Once switched to rate 11520 I can download image within half hour. Some other people also tried a different rate, like 57600, which can work too with a little bit longer download time.
One another alternative workaround might be to rename config.text to config.backup in rommon, then tried to boot up the switch with new image. By removing config.text the switch will not have vtp mode client configured, it should be able to bypass VTP client mode bug and boot the switch without need to go back to old image. After switch is booted with new image, we can just to the following to recover the configuration:
-rename config.backup config.text
-copy config.text running-config
The process is the same as the process of password recovery. This alternative work-around haven’t been verified but is worth testing.