How to Copy an IOS Image to a Cisco Router from ROMmon Mode
Recover a router with a missing or corrupt IOS by transferring an image over TFTP from ROMmon.
Overview
If a Cisco router’s IOS image is missing or corrupt, it drops into ROMmon (ROM monitor) mode. From there you can transfer a valid IOS image over TFTP to restore the router. This guide walks through the process.
Copying an IOS image from ROMmon mode.
Warning: Only perform this on equipment you own or are authorized to service. Use a Cisco IOS image you are licensed to run.
Key Takeaways
- ROMmon appears when a valid IOS can’t load.
- A TFTP server hosts the IOS image on your PC.
- ROMmon variables tell the router where to fetch the image.
- tftpdnld downloads the image into flash.
Prerequisites
- A console cable to the router and terminal software.
- A TFTP server on your PC with the correct IOS image.
- An Ethernet cable between the PC and the router’s first interface.
- The correct IOS filename for your router model.
Set ROMmon Variables
1. At the rommon> prompt, set the router IP: IP_ADDRESS=192.168.1.1
2. Set the subnet mask: IP_SUBNET_MASK=255.255.255.0
3. Set the default gateway: DEFAULT_GATEWAY=192.168.1.2
4. Set the TFTP server (your PC): TFTP_SERVER=192.168.1.2
5. Set the file: TFTP_FILE=c2800-ios.bin (use your image name).
Download the Image
1. Connect the PC to the router’s first Ethernet port and start the TFTP server.
2. At rommon>, run: tftpdnld
3. Confirm the prompt to erase flash and download.
4. Wait for the transfer (exclamation marks show progress).
Boot the New IOS
1. After download completes, reset the router: reset
2. It should boot the new IOS image.
3. Verify with: show version, and set the boot system command in config if needed.
Troubleshooting
Problem: TFTP transfer times out.
Solution: Check cabling to the first interface, IP settings, firewall on the TFTP server, and that the server is running.
Problem: "Invalid IOS image".
Solution: Use the correct image for your exact router model and verify the file isn’t corrupt (checksum).
Problem: Router still boots to ROMmon.
Solution: Set the boot variable/confreg correctly, and ensure the image copied into flash.
Problem: Wrong config register.
Solution: Set confreg to 0x2102 for normal boot after recovery.
Conclusion
ROMmon recovery restores a Cisco router with a bad IOS: set the network variables, host the image on a TFTP server, run tftpdnld, then reset. Use the correct, licensed image for your model, and verify with show version once it boots.
