Following is a quick listing of the commands you need to use when upgrading the IOS firmware on your Cisco router series 1600, 2000, 2500, 3000, AS5100 and AS5200. You should consult the Cisco web site to upgrade other devices. The process involves two phases: one, set the flash to read-write and reboot; two, download the firmware and reboot. You must setup a TFTP server and make the IOS binary file available for download. If your router is not on the same network segment as your TFTP server, be sure both devices have a default route configured so that they may access one another. I recommend using a Linux box for your TFTP server, and limit access to the service with both ipchains/iptables and the tcp-wrappers hosts.allow file. The following sequence of commands can be entered via the console port, or by telnet session. I recommend you have access to the console port if something fails . . . you’ve been warned!
enable conf t config-register 0x2101 ^Z wr mem reload
The router will reboot and the flash will now be in read-write mode. This is called “boot mode.” Avoid saving anything in this mode and answer no to any prompts about saving your current configuration. If you do save your config while in this mode, it may be partially or completely erased…
enable conf t config-register 0x2102 ^Z copy tftp flash it’ll prompt for ip address… it’ll prompt for filename… use same name to save as… when asked about erase say YES to confirm… reload answer NO to save current config answer YES to continue with reload
If you pray really hard, and offer up the right sacrifices, at this point you’ll be looking at a successful router upgrade! If connecting via the console port, make sure your terminal settings are as follows:
VT100 9600 bps 8 data bits 1 stop bit no parity no flow control