If you need to recover/update the image on your router or switch, the MAC offers a simple process that doesnt involve installation of external tftp software.
MAC tftp service 1. sudo launchctl load -F /System/Library/LaunchDaemons/tftp.plist (run on terminal) 2. sudo launchctl start com.apple.tftpd (run on terminal) 3. Copy the images to /private/tftpboot 4. Ensure the PC has an IP address reachable from the switch/router (direct cable / LAN) 5. Run the commands from the router/switch.