Original: http://www.shadowandy.net/2012/03/asus-rt-n66u-tomatousb-firmware-flashing-guide.htm
K26RT-N is appropriate for the RT-N66U. Go ahead and pick the latest release by date. Inside that directory you want the to pick the Asus RT-N66u 64k. The 64k in the name means that 64k of flash memory will be used as NVRAM. Inside that directory the .trx file with AIO in the name has all possible features compiled in and enabled. If this is your first time installing, AIO is a good jumping off point.
The steps are simple, you will need to:
- Connect the ASUS RT-N66U to your network
- Start the firmware restoration process (using firmware restoration utility in the ASUS Utility package) so that it is searching for router
- Put the ASUS RT-N66U into firmware restoration mode and start the firmware restoration process
Before you proceed, pull out the power cable to your RT-N66U and have a pen ready to press the reset button (between the USB ports and WAN port)
- Launch the firmware restoration utility (this is one of the tools in the Utility you installed earlier)
- In the firmware restoration utility, browse for the TomatoUSB firmware you have downloaded earlier
- Start the firmware flashing and a prompt should appear stating that it is an incompatible firmware. Proceed to the next step.
- Press and hold on to the reset button
- While holding down the reset button, plug in the power cable so that the RT-N66U turns on. Note: Keep holding the reset button until the power led starts to flash (on and off). When power led starts flashing, release the reset button and proceed.
- On the firmware restoration utility, agree to the prompt saying that it is a incompatible firmware. The utility should be scanning for device. Proceed to the next step
- Wait until the flashing is complete
- The router will automatically power cycle when it is complete
It is always a good practice to clear out the previous settings (in NVRAM) whenever you flash to different firmwares. This is true for PC BIOSs as well. In this case, it is required to flush out the NVRAM from values that may have been previously stored by the stock firmware that are no longer valid for TomatoUSB.
You can either flush the NVRAM either through key presses or through web admin.
- Power off the RT-N66U
- Press and hold down the WPS button
- While holding the WPS button, plug in the power cable to turn RT-N66U on
- Keep holding the WPS button for 30 seconds before releasing The router should reboot
- Congratulations. The NVRAM has been cleared.
The TomatoUSB administration web should be at http://192.168.1.1. If it is not, do a “ipconfig” or “ifconfig” and navigate to the gateway address with your web browser. If you are not able to get an IP address from DHCP, you might want to set your computer’s IP address to 192.168.1.2/24.
When prompted for a login, the default is:
- User: root
- Pass: admin
Once you are in, follow the next step to clear out the previous settings
- Navigate to Administration -> Configuration
- Under Restore Default Configuration, select “Erase all data in NVRAM memory (thorough)
- Click “OK”
- Wait for the router to be ready
READ ME FIRST:
Skip the instructions in the original post. Read docbill's and AaronCompNetSys' instructions first.
Especially the second link, with the process to simply skip the unnecessary and frankly crappy Asus software:
1. docbill
2. AaronCompNetSys
(thank you both!)