Why is your Cisco router failing to load its IOS image during boot? Learn how missing or corrupt IOS files cause boot failures and how to recover using ROMMON mode—essential for Cisco Certified Field Technician (CCT) exam success.
Table of Contents
Question
A Cisco router fails to load its IOS image during boot. What is the most likely reason?
A. The startup-config is corrupted
B. The flash memory is full
C. The IOS file is missing or corrupt
D. The router has an incorrect hostname
E. The NVRAM battery is dead
Answer
C. The IOS file is missing or corrupt
Explanation
If the router cannot find a valid IOS image, it may enter ROMmon mode.
The most likely reason a Cisco router fails to load its IOS image during boot is that the IOS file is missing or corrupt.
- During the boot process, the router performs a hardware check and then attempts to load the IOS image from flash memory. If the IOS file is missing (deleted, renamed, or not present) or corrupt (damaged file), the router cannot load the operating system and will enter ROMMON (ROM Monitor) mode.
- Common causes include accidental deletion, incomplete or failed upgrades, or file system corruption in flash memory.
- When this occurs, the router displays error messages such as “cannot find image” or “bad magic number,” and drops into the ROMMON prompt, awaiting recovery actions.
- Recovery typically involves using ROMMON mode to load a new IOS image via TFTP, USB, or Xmodem, or pointing to a valid image if one is available.
A missing or corrupt IOS image prevents the router from loading its operating system, resulting in boot failure and entry into ROMMON mode.
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