Boot Image Recovery on a Cisco ASA Firewall

Here are the required steps to recover from a missing or corrupt boot image:

• Connect a console cable from the ASA to your computer and open up a serial connection using Putty
• Disable any software firewall on your computer
• Install TFTP server software on your computer – I used Solarwinds TFTP server
• Place the Cisco software image in the TFTP-Root folder (asa821-k8.bin) and start the TFTP service
• Assign a static IP address to your computer – I used 192.168.20.1 (an address outside of my existing subnet)
• Connect an Ethernet cable between your computer and port 0/0 on the ASA
• Power off the ASA then power it back on
• Press the escape key to boot into ROMMON mode
• Enter the following commands in the ASA (the first part of these commands must be in caps)
  rommon #1> ADDRESS=192.168.20.10
  rommon #2> SERVER=192.168.20.1
  rommon #3> GATEWAY=192.168.20.1
  rommon #4> IMAGE=asa821-k8.bin
  rommon #5> PORT=Ethernet0/0
• These commands assign an IP address of 192.168.20.10 to port 0/0 on the ASA and tell it to look at your TFTP server 192.168.20.1 and to select the ASA software image.
• Next, execute the command to transfer the image from the TFTP server to the ASA
  rommon #6> tftp