Never Ending Security

It starts all here

How to flash a rom with DD-WRT firmware on an Asus RT-N66U router.

In this guide we are assuming that you have installed Asus original firmware on your router.
Otherwise it would be useful to install the original Asus firmware first, before you start to minimize any errors.

Open your webbrowser and go to your router login page, mostly at
Enter the login credentials and go to Administration > System and set the option for “enable telnet” to yes.
And don’t forget to click on “apply” on the end of the page to get telnet enabled.

Open up a command-line, to connect with your router over telnet by entering the command:
$ telnet
Enter your router login credentials when this is asked, when successfully connected run the command:
$ strings /dev/mtd0ro | grep bl_version
This will output something like this: “bl_version=”
And tells what boot loader version is installed on your router.
If this is or lower, then your router only runs with 32k NVRAM.
If it is or higher then your router runs with 64k NVRAM.

Now you know if you need the 64k firmware version, or just the normal version (32k) for your router.
And saves you from potential bricking your device by using an incorrect firmware version.

If your router runs only with 32k NVRAM, you can upgrade the boot loader to a newer version.
In order to make it running with 64k NVRAM, in this guide i will not go into the boot loader upgrade process.
A guide about this can be found at:

If you downloaded the correct firmware version, you can upgrade or flashing it to the device as described in the next steps:
Go back to the terminal again, and check if the telnet connection to your router is still up and running.
If not, reconnect your terminal once again with the router.
Now we need to clear the router’s NVRAM, by using the command:
$ mtd-erase -d nvram
If the output shows something like: nvram successfully erased, you may have to restart the router with the command:
$ reboot
Once the router is completely rebooted , point your webbrowser to and login to your router.
Go to Administration > Firmware Upgrade > New Firmware File and click on “Choose File” and select the new .TRX firmware you dowloaded.
And click on “Upload” to start the firmware upgrading process.
Once the upload process is done, do not restart the device but open up the command-line again, and telnet into your router with the command:
$ telnet
And enter the following login credentials, for username: “root” password: “admin” (both without the ” ” signs)
Now we have to erase the NVRAM again, by entering the command:
$ erase nvram
And reboot the device, by entering the command:
$ reboot
after the reboot you are good to go, and can setup your login and username on the webpage


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