We recently wanted to swap our existing WS-SUP720-base with a WS-SUP720-3B in a 6513 chassis.
Had the existing configuration config saved in a txt file and replaced the supervisor. Booting went fine and we pasted in the original config. There was one failure message about unnsupported command but didnt take further notice.
"boot system flash sup-bootflash:" was probaly the line that the 720-3B didnt support.
After wr mem and reload it went in continious loop and rebooting due to inncorrect boot device. Had to put back the old supervisor and have now the 720-3B in a 6504 chassis. Tried some commands in rommon, but are not getting any further. Any suggestions?