RouterGeek

When would you need this: If your router flash, or IOS file are corrupted, you can use this procedure to install a new IOS file. Also, when you plan to upgrade your IOS file you can use this procedure.

Special Requirements: The router flash size should be enough for the new IOS file.

Before starting the procedure of IOS upgrade or installation, you will need to install TFTP server software on a PC connected to the router Ethernet interface. There are many free downloadable TFTP servers’ software on the Internet, however, our recommendation is Free TFTP Server 6.0.

Afterwards, you make sure to direct the TFTP server to the folder containing the new IOS image that you have.

If you are using this procedure to upgrade the IOS file and you router works fine, it is preferred to backup the old IOS file before starting the upgrade procedure. For this purpose, refer to the IOS backup procedure . 

1. Create a console connection with the default settings (9600 baud, 8 databits, 0 parity bits, 1 stop bit, no flow control).

2. If your flash or IOS file are corrupted and your router goes directly to router boot mode (Router(boot)#), go to step 4. If your router has some problems and boots into the ROMmon mode directly(rommon 1> or >), go to step 3. If your router boots normally, interrupt the router boot sequence by pressing Ctrl-Break once the router is powered on. This will take you to ROMmon mode with the prompt:

rommon 1>

Or

> 

3. Change the value of the configuration register to 0x2101 to instruct the router to boot into router boot mode. Afterwards, reload the router.

If you have the ‘rommon 1>’ prompt use the commands:

rommon 1> confreg 0x2101

rommon 2> reset

While if you have the ‘>’ prompt, use:

> o/r 0x2101

> i

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Read the rest of the article in the Router Geek Book: Guide to Cisco Routers Configuration