Answer: Any suggestions listed/suggested here are just that - suggestions.
While the steps listed should be relatively safe, you assume any and all risks of "bricking" your router.
Go to the ASUS Page..
Drivers And Downloads..
Select Your OS..
I am using Win7 64-bit..
ASUS RT-AC66R Utility version 18.104.22.168
NOTE: You will come to find out that the AC66R is often listed with AC66U, the AC66U tools and firmware work fine with the AC66R
OS Supported: Win 2003 / Win XP / Win Vista / Win 7 / Win 8
Be sure in the description, it has the "Firmware Restoration" (when installed, start button/All Programs/ASUS Utility/RT-AC66U Wireless Router/Firmware Restoration)
Download, extract with an Unzip tool (like 7-Zip, WinRar, or PeaZip) and install
Also, under Firmware.. Grab a couple versions of the firmware - Probably not necessary, but just in case. :)
ASUS RT-AC66R Firmware Version 22.214.171.124.374.2239
Note: This does say it is Beta (at the time of this posting)
ASUS RT-AC66R Firmware Version 126.96.36.199.374.2050
You may want to also download a couple of the PDFs for documentation as needed.
Googling, we do see that AC66R is supported under Tomato.. However, that is outside this discussion. :)
I have used PolarCloud's firmware before and has worked fine on the devices I used it on.
But, because I have used DD-WRT in the past with success with an old LinkSys WRT54G..
Go to - http://www.dd-wrt.com/site/index
We do find the AC66R under AC66U in the "Router Database" on the DD-WRT site:
Type in 66u (the 66u is using the same firmware as the 66r).
Select the one for: Asus RT-AC66U
Good Information about the router..
There is a Wiki Page there too, which goes through quite a number of steps, intermediate steps to upgrade to Merlin, etc. As you will soon discover, I did not go through that.
Be sure that the Ethernet cable is in Ethernet connector of your laptop/desktop. In Networking, it will be helpful to temporarily disable wireless (sometimes called Wireless Zero - I just simply right-clicked and disabled the Wireless connection) on your laptop as well as it also wants to use IP:192.168.1.1 (by default, yours maybe different).
The other end is in one of the 1-4 ports and not in the WAN port.
In Windows, click the start button/All Programs/ASUS Utility/RT-AC66U Wireless Router/Firmware Restoration
Program should come up..
Click the browse button to locate the firmware you want to upload..
Once you have loaded in the firmware
Click Upload Button
It will try to search out the router..
At this point, you will need to grab a pen (recommended), toothpick, or.. To press in the reset button and keep pressing it in..
And the instant you see the Firmware Restoration start uploading, release the reset button. NOTE: Since I completed this previously, there may be some variation in the screen prints here, but the process does remain the same
NOTE: If you see the message: "The wireless router is not in rescue mode." You may have to try this process a couple times to get it there. I was not able to complete this the first time either. :) Be patient with holding down the reset. I know the DD-WRT forum and site is big on the 30-30-30 process/procedure and to be honest is good measure to be sure that folks hold in the reset enough time for the firmware to engage, and is also discussed in the Peacock document as well (see below). The ASUS router reset takes time to reset and using the firmware Restoration tool was the best way for me to see when the appropriate amount of time was needed to upload. Maybe I was missing it, I could not tell when the lights were slow or using the 30-30-30 process and those processes may work fine for other folks, but didn't work for the router I was re-setting.
The utility will show progress and complete. It will also restart the router.
System Recovery will complete.
Wait for the router to start and the lights to come up.
You should see:
Port number: 1 or 2 or 3 or 4
5 Ghz is flashing
You should be able to close the Firmware Restoration tool at this point.
Once router is up, you should be able to navigate with a web browser to
http://192.168.1.1 and login. DD-WRT does immediately force you to set the login and password.
Since the firmware on coming up, does force a username/password change, you should not need this, but if you don't have the standard login/password to DD-WRT - if memory serves a reset on the router should reset the account as well, have a look on this page- http://www.dd-wrt.com/wiki/index.php/Hard_reset_or_30/30/30
Login and proceed as normal into the router.
HELPFUL LINKS AND BACKGROUND INFORMATION:
I did watch the YouTube Video from "Charlie Tango" first and he said the same thing, he was able to go right to the DD-WRT version fo the firmware without having to go through the intermediate steps.
NOTE: Take the information from the Youtube video kind of like going to a buffet lunch. You are not going to like or need everything from the video. Pick and choose what you need and leave the rest. I ** WAS NOT ** able to use TELNET or clear NVRAM, putty, etc. All I could do is use the tool provided by ASUS to upload the firmware. The video does have informative components of it.. I was not able to get to the Web UI in the first place.
There are some helpful pages and such listed on the DD-WRT Wiki page.
Some of the information can prove to be helpful:
The Peacock Page - http://www.dd-wrt.com/phpBB2/viewtopic.php?t=51486
How to set a static IP - http://www.dd-wrt.com/wiki/index.php/Static_IP