Exploring Cisco Router Boot Processes

Q: My old Cisco 2600 router has stopped responding after our last power outage. When I logged in with the console cable, it displayed a ROMmon>prompt. How can I recover from that?

– Matthew

A: This behavior can result from several issues, and to understand them, we need first to explain the Cisco 2600 boot process.

Under normal circumstances, a typical router — once powered on — goes through a predefined boot process, which is programmed into its read-only memory (ROM).

The ROM instructs the router to load its operating system from a specific file that can be located locally in the router’s flash memory or remotely in a trivial file transfer server (TFTP server). The file is a binary file with a .bin extension and has a name that contains the hardware platform it is suitable for — Cisco 2600, in this case — and the functionality that is provided by this file.

For example, a Cisco 2610 router operating system file name is c2600-i-mz.122-46a.bin. This file is for the basic routing features only (as indicated by the letter “i”); it is compressed (as indicated by the “mz” letters); and it is for version 12.2(46a).

If the router is unable to load the operating system file, it fails into a special mode called ROMmon (ROM monitor), which is what you are experiencing. There are many reasons for not loading the OS file: It’s corrupted or missing; it’s the wrong file type (e.g., 2690 file for a…


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