DD-WRT on the Asus RT-N66U – with 64K CFE

UPDATE March 11 2014: I recently updated to the latest K3.x build (23598). I can confirm the following:

  • It is not necessary to upgrade your CFE if you intend to use a K3.x build.
  • USB & MMC support is now working.
  • It is possible to install Optware following these instructions: Optware The Right Way – Take 2
  • Enabling QoS results in reboots every few minutes, or more regularly if under load.
  • Apart form QoS issue above, it seems stable.

UPDATE Jun 10 2013: It would seem that Asus have released a new hardware variant of this model (B2) which is not compatible with this guide. Before you do anything you must check that you have an original hardware version. You have been warned.

UPDATE Nov 20 2013: Since writing this guide, the DD-WRT builds available have improved significantly and as such, the process of flashing them is probably a lot simpler. I am still running build 20363 which I originally flashed, when I have time I will try the new builds. When I have done so I will update this guide accordingly, however until that time you should probably not use the guide below and instead refer to the DD-WRT forums (linked below).

So today I received my fancy new router, chosen because it is a beast and from a quick peruse of the DD-WRT wiki and forum, it seemed I would be able to load DD-WRT on it without too much trouble.

For those who don’t know, DD-WRT is an open source, community maintained router firmware which can turn a consumer router into something any sysadmin would be proud of. I personally love it for the hundreds of features, easy to use UI and active community. From the first time I used it, DD-WRT compatibility has been a prerequisite for any new router purchase.

Check out the features here: What is DD-WRT?

From experience, flashing DD-WRT on a router can be challenging and has been known to result in an expensive paperweight or two so the golden rule is read all the forum threads you can find. This is particularly true if you are dealing with a newish device, since the kinks are probably being worked out and so it is important to have all the latest info before you start.

I have to give full credit to the DD-WRT community for making this possible, so all I want to do here is provide a write up of my experience to try and pull all the information together. Special thanks to Fractal for providing the 64K CFE compatible build.

N.B. This guide includes upgrading your CFE to 64K and at the time of writing means that you cannot install a standard DD-WRT firmware, Fractal has been kind enough to compile a 64K CFE compatible version which you must use.


  1. Fire up the new router, hook it up to your PC with an ethernet cable and point your browser to I aborted the Asus setup wizard it tried to take me through and just jumped straight into configuring manually.
  2. Install the latest version of the Merlin flavour of the Asus stock firmware. You need to do this because it supports SSH, which makes life easier and allows you to display the version of the CFE, which tells you whether or not you need to manually update the CFE.
    You can simply download the latest .trx file from Merlin and flash it using the router’s web GUI.
    IMPORTANT NOTE: It is essential to upgrade to the latest Merlin firmware before upgrading your CFE. If you don’t, you will end up with a brick.
  3. Let the router flash the Merlin firmware and wait until it has rebooted and settled down.

Upgrading the CFE:

UPDATE: There have been reports recently that flashing recent versions of the stock (and so also Merlin’s) firmware result in CFE version However, equally others have not found this to be the case. My suspicion is that ASUS has loaded units manufactured more recently with the CFE. You must flash the latest Merlin build and verify that the CFE is at version or higher using the GUI. If it is, you can skip this section – if not, you’ll have to update it yourself.

  1. Using your browser of choice (IE sucks by the way), load up again and click on ‘Tools’ on the left-hand menu. This will take you to a page where you can see the current CFE version. This will be currently. We will be upgrading to
  2. Under ‘Administration’ enable SSH and also Telnet (just in case).
  3. Follow these instructions to perform the update.
    1. Because you used the Merlin firmware earlier, you can easily use SSH to connect to the router to do this. If you are not familiar with SSH, you should probably not be attempting this.
    2. I hadn’t plugged my router into the internet yet, so I used SCP to transfer the cfe_n66u- file to the router instead of downloading it directly using wget as the guide suggests, but either is fine.
    3. Here’s the output from my upgrade:
      ASUSWRT RT-N66U_3.0.0.4 Sun Dec 16 01:33:41 UTC 2012admin@RT-N66U:/tmp/home/root# ls -alh
      drwx------ 3 admin root 80 Dec 31 12:10 .
      drwxr-xr-x 3 admin root 60 Dec 31 1969 ..
      drwx------ 2 admin root 60 Dec 31 12:04 .ssh
      -rw-r--r-- 1 admin root 156.5K Dec 31 12:10 cfe_n66u-
      admin@RT-N66U:/tmp/home/root# tar -zxvf ./cfe_n66u- 
      admin@RT-N66U:/tmp/home/root# ls -alh
      drwx------ 3 admin root 160 Dec 31 12:11 .
      drwxr-xr-x 3 admin root 60 Dec 31 1969 ..
      drwx------ 2 admin root 60 Dec 31 12:04 .ssh
      -rw-r--r-- 1 admin root 156.5K Dec 31 12:10 cfe_n66u-
      -rw-rw-rw- 1 1000 1000 130.3K Oct 2 2012 cfe_n66u-
      -rwxrwxr-x 1 1000 1000 1.8K Dec 3 2012 cfe_update.sh
      -rwxrwxr-x 1 1000 1000 90.5K Dec 3 2012 diff
      -rwxrwxr-x 1 1000 1000 8.8K Dec 3 2012 nvsimple-mipsel
      admin@RT-N66U:/tmp/home/root# ./cfe_update.sh /dev/mtd0ro
      [1/4] Dumping default NVRAM settings from original CFE…
      nvram header found:
      [2/4] Preparing new CFE…
      nvram header created:
      [4/5] Checking differences between NVRAM from old and new CFE's
      --- nvram_orig.txt2010-12-31 12:11:30.359770287 -1200
      +++ nvram_updated.txt2010-12-31 12:11:30.419770287 -1200
      @@ -1 +1 @@
      @@ -16,0 +17 @@
      If you see only two differences: one is for 'bl_version' variable change
      and second is a new 'odmpid=ASUS' variable then all goes well!
      [5/5] Flashing new CFE…
      Do you want to flash a new CFE bootloader that? [y,n]y...flashing…
      Update completed. Old CFE is stored to cfe.old file, a new one - to cfe.new
      It's strongly recommended to store them, just in case.
      Please note, your personal MAC addresses in there, do not distribute them.
    4. Really do back up your old CFE file, the script creates a backup for you, all you need to do is SCP it off and save it somewhere safe. You’ll probably never need it again, but if you do, you’ll really need it.
      • You can do this using SCP. On a Linux or OSX machine you can use the terminal:
        scp root@ .

        or you can use FileZilla or WinSCP to connect as an SFTP client if you want a nice gui to browse the router and download the file. This is probably the easiest way for Windows users.

    5. Check that the new CFE version is reflected in the web GUI under ‘Tools’. I didn’t seem to have to reboot for the change to be reflected.
    6. Re-boot the router. I just hit the power button.

Flashing DD-WRT:

  1. Flash Fractal’s special 64k CFE compatible firmware. I downloaded version 20363 from here, however there is a new version 21402 available here. You can just flash this through the web GUI as usual.
    1. Do check here for any newer builds. If you see a newer build, really do go and read the forum to find out how people are getting on with it.
    2. Make sure you flash a 64K build. These can be identified by the ‘_64K.trx’ file ending. The other builds are 32K and will result in bricking.
  2. Let the router flash the DD-WRT firmware and wait until it has rebooted and settled down for at least 5 – 10 minutes. Mine seemed to finish very quickly, but the advice of the forums is to give it some time.
  3. Perform a 30-30-30 reset to clear the NVRAM and round everything off.
    1. N.B. This router model uses the WPS button instead of the usual reset button. (Like the RT-N16).
  4. All done 🙂

At the time of writing I have just finished this and so can’t comment on stability just yet, but it seems solid enough and I have had no trouble configuring it. In 20 minutes I had swapped out my old router and the RT-N66U is now managing my whole home network. Seems good so far.
UPDATE: I have been running this build for several months now and I can confirm that it is solid as a rock.

This post was written to collect all the information at the time of writing together. Obviously it may get out-dated. As such it is essential to read the following for the latest updates before you attempt this yourself:

180 Comments on “DD-WRT on the Asus RT-N66U – with 64K CFE”

    • Unfortunately I no longer have a stock router to check on – I only have the one and it’s now got DD-WRT on it 😉
      It may be that the tools menu is something that the Merlin builds add, but I think it is in the stock one too. This should help: http://www.lostrealm.ca/temp/asuswrt-sysinfo.png

      On a side note – I really would load the merlin firmware first. It will make your life a lot easier as it will allow you SSH access and will show you if you have managed to update the CFE properly.
      At the very least, you MUST upgrade to the latest stock firmware.

      Let me know how it goes 🙂

  1. thanks to this post I got it!
    now my N66u runs dd-wrt and I can used as repeater!! thanks a lot!

    issues: the 5,0ghz does not work, at least for me.
    of course I did the 30/30/30 rule before and after flashing!!

    • I had this issue initially – try selecting your channel manually, some client devices don’t support all channels. I recommend using a tool like NetSpot (OSX) to find a channel that nobody else in the vicinity is using.

      Also, I think I remember reports of issues with ‘N-Only’ mode and that ‘N/A Mixed’ works better. My setting (which work great) are can be seen here: https://charleswilkinson.files.wordpress.com/2013/01/rt-n66u_wireless_settings.png

      I left the advanced settings as default, although there are reports that reducing the TX power can improve stability if instability is a problem.

      • I would like to comment you something.

        I am using the router as Repeater, with the following firmware: dd-wrt.v24-20363_NEWD_2_K2.6_std_usb_nas-RT-N66_64K.trx

        I get internet over Wireless (2.4Ghz) and I give it to my computer via ethernet.

        I have configured as AP a Wireless with 5.0Ghz, which works fine.
        But when I create a virtual Wlan with 2.4Ghz as AP, I have several problems. It’s really inestable. That means that sometimes works, sometimes not.

        Someone nows what is going on?

        Thanks in advance.

  2. Hi Charles!
    You are saying to make a backup of the CFE but not showing how it can be done.
    I did read the post of ryzhov_al and it says how to download and install. And then at the end, how to get the OLD CFE. However, How is the CFE backed up then?
    Thanks for your help

      • Charles, thanks for the update!
        Another question: I know you say to update to latest firmware. I just downloaded Merlin and It will upgrade my 32k NVRAM to 64k. As I can read from many forums it is a major upgrade! No turning back! Could you please confirm me that with a 64k i will get a ddwrt fully working! Sorry to be a pain here… but as their is no turning back, I want to be sure and there are so many people saying different things… I need the advise of a pro 😉

        • Hey Nicolas,
          You are right that it is a significant update, however it isn’t as permanent as you might think.
          If you update the CFE to 64K you can still use the latest Merlin builds or indeed the latest Asus stock builds – they both support 32K and 64K CFE automatically. Additionally, you can take a backup of your 32K CFE and if you really wanted to you could re-flash it to revert the process. Warning – I haven’t tried this.

          That being said, yes, I can confirm that you should easily get DD-WRT up and running and fully working. The only limitation I have found so far is that I can’t install Optware on the internal SD card. Everything else seems fine.

          Also worth noting is that currently the official DD-WRT builds don’t support 64K CFE and as such you will be stuck with Fractal’s build for now. However Fractal has raised a ticket for his changes to be rolled into the official builds so it should get rolled in soon. Keep an eye on the relevant threads for updates.

          Good luck and let me know how you get on 🙂

  3. Charles, i succeeded thanks to you! Thanks.
    Here is something to note:
    After the flash I waited 15-20 min but the routeur did not react. No ping nothing.
    So I decided to turn it off and on again and it came back after another 15-20min of waiting. However, my previous “data” (like PPPOE settings) were still there. I did a factory reset and only then, i did a NVRAM clearance and I waited another 15-20 minutes.
    I am using it now.

    NB: I need advice on a set up for my network. Here are my needs:
    – 99% of my traffic goes to “normal” internet
    – 1% goes through VPN with HMA to use netflix on ATV2 jailbroken. (apple tv)
    – My ATV2 has XMBC so i want to be able to read the data on my NAS but also the netflix without changing network.

    Any idea?

    • Hi Nicolas,

      I’m afraid that I’m not really able to help on that front – network configuration is not my strong point. I would hazard a guess that you want two distinct subnets with a static route between them for the NAS access. However I don’t know how to set that up (or if it is the correct way to do it).
      You may be better off on the DD-WRT forums – sorry.


  4. Hello Charles,
    I worked all day on this routeur and i have a better feedback.
    Basiccaly i followed all you advices and install the Fractal firmware as you know.
    Unfortunately I think there is a bug when using the VPN. I tried so many things and then I deciced to reverse to the original firmware from ddwrt. So I looked at the router database and downloaded and installed the MINI version of DDWRT.
    Since then, my routeur is not answering. No CFE recovery either! Damn.
    I did a 30/30/30 reset and also I push the wps while booting and last but not least I pressed the reset for 10 sec durung the boot time to get the recovery… no luck.
    Any idea?

  5. Another miraculous update Charles.
    I discovered something that is not in the book! Just lucky and recovered the routeur that i thought was briked. (see previous post).

    1) Unplug power cable of the routeur
    2) Turn it on to leave all excess of power…
    3) Press the WPS button
    4) Put the powercord back on and then, after 1 or 2 seconds, press the reset button without releasing the WPS.
    5) Wait a bit and only now release the WPS button while keeping the Reset button on.
    6) Wait a bit more and release.
    7) Wait and try to ping your routeur on (you have fixed IP obvisouly)

    And I swear it worked!!! Wherease i could not ping it before, no recovery, nothing…

  6. Hi Charles…
    Regarding VPN and more particularly HMA, i can tell you now that it is working. However, I only suceeded to make it work using the automatic scrip of HMA. The GUI interface of DDWRT is not working on it… or i failed – but believe me i tried for a long time.
    Mooved now to the lastest build of Tomato Firmaware by shaddy. This one works perfectly on my RT-N66U.

    • Hi Nicolas,
      I have been away on holiday, so sorry for not getting back to you. Glad to see you got it all sorted and thanks for sharing your findings 🙂


  7. Many thanks, Charlie.

    The only issue I experienced was that neither Filezilla nor FTPVoyager would connect to the router (not sure why) and in the end I downloaded putty to do the SSH and inside the putty.zip there was also a pscp.exe command line secure transfer utility. For windoze users, this transfer of the tar file to the router should be the only tricky issue, I think. Otherwise it worked exactly as you describe.

  8. I’m a technical nube and have bought the RT-N66U (like an old lady driving a Ferrari?) to address the distance between our (fibre-optic modem connected) router and the ~15 mainly Apple components in our living room and office.

    I understand that the router won’t work for me out of the box, so I need to flash the router in order to connect via VPN (?). The basic flashing instructions I’ve been sent via Asus won’t work? Am I destined to screw this up? Please advise whether I might simply follow the directions above step by careful step (and while internet connected via another router). Thanks.

    • Hi RDF,
      You should be Ok if you follow the guide, however I would ask why you think that the router won’t work out of the box for you? Flashing DD-WRT isn’t exactly trivial so I wouldn’t advise it for someone not tech-savvy.


      • Hi Charlie – thank you very much for your reply. I intend on using HMA from Europe to gain access to a US server / Netflix / Pandora. May I use it out of the box? The HMA site instructs me that I “need to download firmware DD-WRT firmware for the router. You can download the firmware here: dd-wrt.v24-14929_NEWD-2_K2.6_mini_RT-N16.trx” Am I overcooking this? Thanks.

      • flashing instructions via the HMA Wiki

        Flashing the Router
        In this step you will be installing new firmware on the router. This is needed as only routers with the open source DD-WRT firmware can connect to VPN. The powerful Asus router is great at running this firmware.

        First of all you need do download the DD-WRT firmware for the router (see above).

        Insert the Ethernet cable in the LAN1 port of the router and connect it to your computer. If you have other Ethernet cables connected to the computer disconnect them now – also disable Wi-Fi on the computer (HOW IS THIS POSSIBLE IF I AM REPLACING A ROUTER AND NEED AN INTERNET CONNECTION TO GO TO

        Open your browser and go to and input admin/admin if you are asked and have not set another combination before. If this is the first time you are using the router please follow the setup steps.

        On the dashboard click on advanced settings then firmware upgrade. Click choose file and select the dd-wrt.v24-14929_NEWD-2_K2.6_mini_RT-N16.trx that you have downloaded before. Wait for the setup to complete.

        Once the flashing is complete you will be meet with a screen asking you to give the router a username and a password. Fill out the info as you please.
        You should now be at the main dashboard of your router with the new firmware. The hard part is done.

      • Hmm. Ok, I’m out and about at the moment but I’ll try and drop you an email later when I have a moment. Hopefully between us we can get it sorted 🙂

      • I spent an afternoon with a technician trying to set-up my wan and lan settings on the asus rt-n66u to make it compatible with a movistar hua___ (fibre-optic) modem. Now I was then told that I need to reset the modem to its factory settings in order for the exercise to work.

        Knowing movistar I know that I’ll never have a working internet connection if I have to rely upon their tech support to fix anything unrelated to an initial installation. Tey are really useless (and this saying something as I’ve been using AT&T for 10 years).

        I feel like throwing in the towel on my HMA experiment and returning the asus router. Its a shame really. Am I missing something? Has movistar Spain put the deathlock on HMA? Should it be this difficult? Please advise.

      • Hi RDF,

        Sorry for the slow reply – I have been really busy recently and so have had no time to respond.

        So firstly, the instructions you pasted in your comment look like valid instructions for installing standard DD-WRT on this router without using the 64K cfe (although I have never done this). Did you actually do this or are you still running stock firmware?

        Secondly is the issue that you can’t get the ASUS router to work with your modem/ISP or is it that you can’t get HMA to work?

        If it is the former, a bit of googling gave me this post by someone attempting the same thing who found a solution: http://www.lostinsantcugat.com/2011/10/replacing-my-crappy-movistar-fiber.html

        Hope this helps,

  9. Hi I’m Walter and I’m most looking forward to this router rt-n66u… I saw that on the site (ddwrt ->router database) is not indicated revision or version … if I’ll buy a new model (for example on amazon) is 100% guaranteed that I can install the ddwrt?

    thanks for Your Time


    • Hi Walter,

      I don’t think there is more than one variant of this particular model out there so you should be ok. There is at least one newer model though, so don’t get caught out there.

      Also, don’t rely on any information or builds on the router database. It is always drastically out of date.


  10. Hi. Thanks very much for this tutorial. Before I follow your steps, is this something I can do over Tomato Shibby or should I revert back to an Asus based firmware?

    • I have no idea if Tomato has support for the 64K CFE as I have never used it. I would have to advise to flash latest Merlin build just to be sure. It would be a shame to brick the thing for the sake of five minutes work.

      Good luck 🙂

      • Hi, I just wanted to leave my quick 2 cents. I have the RT-N66R (the retail version of the U) running Tomato (Shibby). I can confirm that Tomato does support the 64K CFE. Mine came with that CFE out of the box, so I didn’t have to upgrade to flash Tomato. But they don’t have a 32K version (that I know of) so if you’re already running Shibby, you’re good.

  11. First, thank you for this guide. Having all this information in one place puts me much more at ease regarding this process. I’m pretty tech savvy but this is my first DD-WRT install and I’d rather not brick my router if I can help it. 🙂

    This is possibly a stupid question, but when I go to download Fractal’s special 64k CFE compatible firmware (version 20363) from the link you provided, the links themselves have .trx file extensions. However, the file that is downloaded by clicking on the links is a .bin file. Is this as it should be? I was under the impression I should be downloading a .trx file.

  12. Nevermind. I’m an idiot. For some reason ubuntu was automatically changing the file extension for me. I turned that off. 🙂

  13. Thank you for the guide Charles. I just received my RT-N66U today, coming from being a long time WRT54G user. I had functional port forwarding with the WRT54G with both stock firmware and dd-wrt micro. For some reason, I could not get port forwarding to work with the RT-N66U with stock firmware or Merlin’s firmware. I updated using dd-wrt.v24-20363_NEWD_2_K2.6_std_usb_nas-RT-N66_64K.trx linked in your guide and port forwarding is working again! Thank you!

    I’m still not sure what was wrong with my settings in the stock or Merlin’s firmwares, as a majority of others seem to have no issues with port forwarding.

  14. Thank you for providing these helpful instructions. Some remarks on how i installed dd-wrt.
    First of all, i bought my “dark knight” at the shop around the corner. It came with the -220 firmware which i first updated to -270. Asus stock firmware does not have a tools menu, but i telnet-ed into the box and asked / grepped nvram for the boot loader version ( As the box was not yet connected to the internet, I put the 64k boot loader onto a usb drive, which was auto-mounted by the firmware. After flashing the boot loader, the nvram bl_version was still set to until i did a factory reset (from the web interface).
    Flashing the current usb_nas-Version from the web interface was a piece of cake, but the box did not reboot by itself, just stopped answering to pings. After a few minutes i switched it of and on resetting the settings with the WDS button. dd-wrt booted then.
    Wireless: the 5 GHz radio wasn’t seen by my smartphone until i manually set the channel to 40. (I am alone on the 5 GHz band, anyway, while 2.4 GHz is rather crowded.) The 2.4 GHz channel cannot be set manually unless the bandwidth is set to 20 MHz. This is probably intentional.

  15. I can’t utilize/connect the Asus due to our Movistar Spain fibre-optic modem (huawei HG8240) being closed/locked. Do you have any suggestions re: how to resolve? – I can’t get support (in english) or from HMA without the user name/password of the modem.

  16. For those who wonder about where barryware has gone: it is down and will be for a few weeks (cf. barryware’s sticky thread at the dd-wrt forum). Therefore, the above mentioned fractal builds are no longer accessible. There is a new one (20801) on ftp://ftp.basmaf.com, however.

  17. hey everyone, has anyone tried to install the 20801 build? any thoughts on whether this will work? if not, is there any other place i can get build 20363 since Barry’s FTP site is down?

    Thanks much!

      • hey,

        I updated using 20801 and latest version of Merlin firmware. the CEF is now embedded merlins firmware it looks like so need to do any of the manual steps. The process was extremely easy. Update to merlins firmware, performed the reset using WAP button, verified CEF version, updated fractals, reset using WAP button and thats it.

        Hope this helps everyone.

  18. hi charles, rajesh here, i bought this router for a client who wanted to use happy vpn, i successfully upgraded the cfe to 64k as per your instructions, unfortunately barry ware ftp site is down and i cant download fractal’s firmware. also loading the recommended firmware from ddwrt website results in no ping from the router side. i am using the wps button to do the hard reset, can anybody share a few ideas on how to load ddwrt on this router with the non availibilty of fractal firmware.

  19. thanks a ton kabadisha, the ftp site is not opening atleast here in mumbai india, hv tried 2 different isp’s. will revert after flashing this build. thanks once more

  20. Tried fractal build 20969 just yesterday. Seems to work well so far (2.4 & 5 GHz), but i didn’t try anything spiffy. On the forum some problems with mounting external volumes are (still) reported, didn’t try that, however.

    • Thanks like the update Thomas. I should probably try upgrading at some point, but I just can’t face manually re-entering all the config again. It’s a shame we can’t carry config backups across builds.

  21. Hey Everyone;

    Trying to follow the guide on here to get DD-WRT installed on my RT-N66U unit I just purchased. I’m following along the steps here and go to the point where I flash Merlins build first using the stock GUI and uploading the latest zip file ( RT-N66U_3.0.0.4_270.26b.zip ) from his website.

    When I goto verify under TOOLS –> Bootloader (CFE) it already says, and per the instructions it should still be on Can anyone shed some light? Thanks in advance

    • I can validate your experience — mine did the same and I was able to skip to the install procedure. But I’m not sure why it showed when, according to the guide, it should have still been

      • Thanks. So here’s the situation. I flashed the dd-wrt.v24-20979_NEWD_2_K2.6_mega-RT-N66_64K.trx file, and when it was done rebooted. I let it settle for 15 minutes before logging into it, pinging it, etc. After I let it sit, before I did anything, I turned it off, and held down the WPS button and turned it back on. I let go of the WPS button after 30 seconds.

        I let it sit a little bit and then tried to access Now I get an ASUSTEK – CFE miniWebServer window, with a browse and upload button to upload firmeware.

        Shouldn’t I be seeing the DD-WRT GUI by now? What did I miss??

    • Apparently the merlin recently added the 64K bootloader update to his ROM so you don’t have to do it manually now 🙂
      I will update the guide tonight.

      UPDATE: Incorrect. More recently manufactured units have the 64K CFE already loaded. I have updated the guide accordingly.


  22. nevermind I apologize…I let it sit a few more minutes, and tried again, and now I’m in DDWRT. SWEET! Thanks !!

  23. Hello!

    I need some help. I have a ASUS RT N66U router that I have DD-WRT installed on. I have been experiencing including (that I have noticed):
    – WAN history limited to only current month
    – Configuration of VPN erases existing NAT, SERVICES and other settings
    – It seems that sometimes I have Internet traffic slow downs that rectify when I reboot the router. Traffic does not appear to be greater than what I had when I had my WRT54GS router with DD-WRT v23x installed on it.

    From my research it appears that there is some sort of memory (VRAM) limitation that maybe the cause when using N66U with DD-WRT.

    If I understood my research correctly and this is indeed the case then:
    (1) will performing the 64K CFE update noted in this article rectify my issue(s)?

    (2a) If not, has anyone had this issue too and perhaps knows what the solution may be and direct me to the website or solution source?

    (2b) If the 64K CFE is the solution, then can I just perform noted above on my current DD-WRT (v24-sp2 (06/08/12) big SVN revision 19342) as described on http://www.dd-wrt.com/wiki/index.php/Asus_RT-N66U?

    (2b-1) Or must I re-flash back to some previous ASUS firmware.

    Any assistance in the matter would be greatly appreciated.

    • Hi Anwar,

      In answer to your questions:
      1) Yes, this will probably solve your issues. The strangeness you are experiencing would be caused by the 32K CFE.
      2) You must flash to a firmware which can support both 32K and 64K CFEs. This means that you can’t do it on any DD-WRT build. You must flash the latest Merlin build first, then follow the guide above from the ‘Upgrading the CFE’ part.

      Hope this helps 🙂

  24. I loaded the latest Merlin build but the CFE version still states that it is and NOT like it needs to be. What do I do now?

      • Problem is mine is and I have to have to upgrade to The script doesn’t allow upgrading from

      • Ok I just edited the .sh file and changed all the entries to, it worked perfectly, thanks for your help.

      • Awesome! Sorry I didn’t get back to you – I’ve been really busy recently. I don’t think I was going to be very useful though – My suggestion would have been to upgrade to the latest ASUS build first. However you probably tried that already.

        Glad you found a workaround. Even more glad you shared it. Thanks 🙂

  25. Thanks for the simple guide! I purchased my RT-N66U from Amazon a couple of weeks ago and loaded dd-wrt on it straight away. It looks like the CFE was already at 64KB with the stock Asus firmware (v3., as I didn’t have to do anything after confirming it with Merlin.

    Also, dd-wrt defaults (and limits) to a somewhat low 4096 maximum IP connections. With the amount of memory available in the RT-N66U, you could easily raise this to 16384 or even higher. There’s information on the wiki about how to increase it outside of the GUI here.

  26. Hello,

    First I want to say I am stupid because I like to follow tutorial but not every step (same when I am cooking and then I wonder why it does not taste good :D)

    Here what I have done:
    I played a bit with the router, test file transfer etc.
    1. I reset to default settings via web interface.
    2. I put latest Merlin firmware.
    2bis. I did not put CFE version because it was already there
    3. I put the mini firmware from DD-WRT page:
    via the web interface.
    4. I let 1h go (I was eating)
    5. I performed a 30/30/30 hard reset and nothing….

    I tried to perform 30/30/30 hard reset several times, I even tried with the reset button, the only thing which changed is that now the LED of the 2.4GHz and 5GHz are off now.

    I can’t ping the router even if I only have my ethernet connection enabled with fix IP (I tried and DHCP gets nothing and wireshark just see request from my laptop, no answer from any kind form the router, no broadcast for any other devices than my laptop.

    Do I really have a 140€ brick or do you have an idea for me? (please don’t say FOLLOW THE TUTORIAL STEP BY STEP).
    I am the only one to blame and I know that but belgian beers for the one who save me here 😉

    • Oh dear.

      Ok, so I think you know where you went wrong. However, in the interest of knowledge sharing, the reason that you have a brick is that the normal DD-WRT builds do not support 64K CFEs. Additionally, even if this feature is introduced, the router database website is always drastically out of date.

      So the solution. Basically you need to flash a build which supports 64K CFEs. I personally recommend you try to flash back to the latest merlin build.

      Your CFE should be in tact so I think you should be able to get the thing into recovery mode and flash a working build by following these steps:

      1. Set your NIC card to static IP, Subnet, Default gateway
      2. Put router into recovery mode by holding down the reset button while powering up the router, wait until the power led is blinking slowly, then release the reset button.
      3. Access the router’s built in recovery mode by issuing in browser
      4. Flash the latest Merlin build.
      5. Follow the guide above from the beginning. No shortcuts this time 😛

      Hope this helps. Let us know how you get on.


      • Thank you for your quick reply!

        So, the thing is I tried to get the recovery mode but whether I use the reset button or the WPS button I don’t have the power LED blinking 😦

        I have another one (ordered for a colleague but he told me I can use it) and so I just need to put the Merlin firmware, and then the DD-WRT you give (because I already have the proper CFE it should be ok?

        Do you know if I send it back to Asus and say it was Dead On Arrival they will give me a new one? Do you think they check if the customer tried to update the firmware? Any I will try!

        • Hmm, that’s annoying.
          Have you tried the (unverified) recovery steps which nicolasargente posted above? It might be worth a shot:

          1. Unplug power cable of the router.
          2. Wait a few minutes to let any remaining charge dissipate.
          3. Press and hold the WPS button.
          4. Put the powercord back on and then, after 1 or 2 seconds, press and hold the reset button without releasing the WPS.
          5. Wait a bit and only now release the WPS button while keeping the Reset button pressed.
          6. Wait a bit more and release the reset button.
          7. Wait and try to ping your router on (you have assigned a static IP obviously)
          8. If you get a ping response try loading and hopefully you should see the recovery console

          In answer to your other questions:

          • If you load merlin’s build and confirm that you already have the CFE you can indeed skip the section of this guide related to upgrading the CFE. This also means that flashing a normal DD-WRT build will brick the device, so only flash the special Fractal build linked from this guide
          • You can probably send your bricked unit back. In my experience for these companies the cost of having highly skilled engineers needed to analyse every returned device for foul play is not worth it. Additionally, if it really is bricked they wouldn’t easily be able to tell how.

          Good luck,

        • So it works fine on the 2nd router! 🙂 Thanks a lot but no luck for the bricked one…
          Being able to watch 1080p movies on my tablet over wifi, that is pretty nice! Let’s see now on the long term if it is still nice 🙂

          I will let you know if Asus refuses to change my bricked router.

          Thank you for your help!

      • Actually it worked!!! I let it for one week and then was out of town for one week and today I was like “humm let’s give it a shot and if it does not work let’s send it to RMA” but it worked!!
        So it is like you said and I put the Merlin firmware, it took something like 5 to 10min to be ready.

        I will let my colleague decide if he wants to put DD-WRT or not!

        HUGE thanks, if you ever come to Brussels let me know, beers will be on me!

        • Awesome to the max. Really glad that worked for you. Thanks for taking the time to update us 🙂
          If I ever find myself in Brussels I may take you up on that beer 🙂

      • yes you can flash with OSX. But later on the GUI for DD-wrt didn’t work for me with firefox. Get afraid i bricked the router because the GUI was always rebooting without making any changes. Then used windows with Explorer and it worked fine. Better have a windows on hand for the flashing

  27. I just ordered this router. When I get it, how do I know if it’s compatible with this updated version of DD-WRT? Can attempting to flash the Merlin cause issues?

    • It should be fine – I don’t think they have released a new hardware revision. Flashing merlin should be safe – It’s based on the Asus stock firmware.
      You will probably find that the CFE is already at the later version so you can skip the steps to update it.


  28. Thanks for a great guide, intuitive and to the point. Its nice when somebody puts the effort in to help un-muddy the water!


  29. I just flashed the 21402 build and for some reason the only interface that works is the wireless. WAN and LAN aren’t working. The router isn’t pulling an IP from the modem and none of the LAN ports seem to be active.

    Any ideas? Do the newer builds not have the virtual crap and interfaces configured correctly?

    • Oh dear. I’m afraid I don’t know – I haven’t tried that build. Someone else might know but you might be better off asking on the DD-WRT forums.

      Sorry I can’t be more help. Please do let us know if you manage to resolve it 🙂


      • Charlie, I appreciate the reply. I gave up on the 21402 and went to 20801 and I still have the same problem. Clearing the NVRAM should revert 20801 back to usable defaults, right?

      • Well… in my frustration I decided to put the old firmware back on the router and start over. The old firmware doesn’t want to seem to go back on the router and ends up just putting it into a connection-less state. I couldn’t put AsusWRT or merlin back on it. So… I decided to go at it again with DDWRT.

        This time it worked. I think the key to the success was my ridiculous adherence to clearing the NVRAM whenever I could because I have a feeling this is what was causing the problem the first time. I cleared the NVRAM, flashed DDWRT, cleared the NVRAM and then cleared the NVRAM once more once I could hit the web GUI again.

        Success with build 20801. I’m not flashing anything for a while. My nerves can’t handle it.

  30. I just bought a new RT-N66U and here’s the steps and results I had with build 21402 (the newest build).

    1. Downloaded Merlin firmware from http://www.lostrealm.ca/tower/node/79
    2. Turned on router, plugged in to computer via included Cat-5E cable (why didn’t they include cat-6?)
    3. In Firefox, navigated to and was forced through awful “setup wizrd”
    (clicked “next”, then “manual” and it still forced me through dumb checks for the cable modem which I had connected to my old router in case I needed internet connection for anything)
    4. In web GUI, clicked on firmware version number at top of screen and then upgraded to the latest Merlin from here: http://www.mediafire.com/asuswrt-merlin/ ( build
    5. Waited till it was done/rebooted
    6. logged in (it changed my password/user back to “admin”, “admin” but that took me some guesses)
    7. upgraded to latest DD-WRT build 21402 from here:ftp://ftp.basmaf.com/Fractal_Builds/21402/dd-wrt.v24-21402_NEWD_2_K2.6_mega-RT-N66_64K.trx
    8. NOTE: it did NOT reboot but instead told me to do manually. I didn’t know how, so I turned it off and unplugged and waited 1 minute
    9. Held in the WSP button, plugged back in, turned on and then (still holding WSP), held in reset button too
    10. counted to 30 seconds, released WSP button, continued holding reset button
    11. counted to 30 seconds, let go of reset button
    12. waited 15 minutes, then in browser went to and saw the recovery screen, clicked to reboot

    That was it! It worked and so far (only a few hours) seems to be working well. one WARNING: on startup, there’s no security on your router’s wifi.

    One question:

    1. How do devices choose which radio to connect to? If I start with a device near the router and it’s on the 5mhz, then I move away to where 2.4mhz is stronger, will it switch?

    I’ll update this in a few weeks about how this build is running, but so far seems solid.

    • Hi Don,
      In answer to your question: it depends on the device. However in my experience once a device has a connection it won’t drop it for another one just because the signal is weak.
      What I do is have 2 separate SSIDs for 5Ghz and 2.4Ghz so that I know which one I’m using.


      • I’m having a problem with this setup right now and I’m hoping you know the answer. When a device connects via DHCP and tries to download a bunch of stuff all at once or in a row (e.g. doing package updates on a Linux computer or updating a bunch of apps via Google Play on an Android phone), the router cuts off the data! They stay connected to the router but cannot reach the internet or even other devices on the network!

        I *think* it’s only for DHCP connections and it *seems* that using a static IP eliminates this issue, but I’m not 100% certain about that yet. Have you noticed this? Is there a setting in DHCP I need to set?

    • Yes. As long as you have the proper Key Phase you’re good. Don I want to thank you for your input on how you got your Flash to work. I was up til 5am yesterday and as of today till 3am. I’m so happy. Thank you so much for being kind enough to share your experience.
      To Charles, thank you for being just as kind and providing this forum. I really appreciate all you both have contripute to me finally getting some sleep. lol! Take care and I’m sure our path will one day cross again.

      • No problem. I’ve been helped by many, many people in the same way so I always post my steps/experiences in the hopes I can help people too.

  31. Hi Charles,
    I´m trying to use openVpn but it doesn´t work. Do you know if openVpn works with build “dd-wrt.v24-20979_NEWD_2_K2.6_mega-RT-N66_64K”

    All the other things work great :), Big thanks for your work 🙂


    • I’ve used openvpn on 20801 and 21402 without any problems. Have you turned on syslog and checked for error messages?

      • Not yet. When i look “ps” with ssh I don´t find an openvpn prozess. I will now flash 21402 and report what happens.

  32. I have now build 21402 running but openvpn doesn’t work yet. Ssh also doesn’t work with the new build. I connect with telnet to look if openvpn prozess is running but that´s not the case.

    Later I will resett everything and do it again. maybe i overlooked something.

    • Hi Ben,

      I think here is the problem:

      12.05.2013 11:56:29 [1862] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:28 syslog: openvpn : OpenVPN daemon (Server) starting/restarting…

      12.05.2013 11:56:29 [1856] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:28 syslog: vpn modules : nf_conntrack_proto_gre successfully loaded

      12.05.2013 11:56:29 [1859] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:28 syslog: vpn modules : nf_nat_pptp successfully loaded

      12.05.2013 11:56:30 [1867] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:29 syslog: vpn modules : nf_nat_proto_gre successfully loaded

      12.05.2013 11:56:30 [1868] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:30 syslog: vpn modules : nf_conntrack_pptp successfully loaded

      12.05.2013 11:56:30 [1869] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:30 syslog: vpn modules : nf_nat_pptp successfully loaded

      12.05.2013 11:56:30 [1866] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:29 syslog: vpn modules : nf_conntrack_proto_gre successfully loaded

      12.05.2013 11:56:30 [1865] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:29 syslog: vpn modules : vpn modules successfully unloaded

      12.05.2013 11:56:30 [1863] From: (x.x.x.x) Fac:3 Sev:3 Msg >>> May 12 11:56:29 openvpn[1610]: Options error: error parsing –server parameters

      12.05.2013 11:56:30 [1864] From: (x.x.x.x) Fac:3 Sev:4 Msg >>> May 12 11:56:29 openvpn[1610]: Use –help for more information.

      12.05.2013 11:56:31 [1870] From: (x.x.x.x) Fac:1 Sev:6 Msg >>> May 12 11:56:30 syslog: vpn modules : vpn modules successfully unloaded

      Do you have any idea ?

      • It’s probably something you have in the “Additional Config” field or perhaps as a startup command. If you were using a different version of OpenVPN before moving to this one it’s possible you’re using a parameter that’s no longer compatible.

        Have you run “cat /var/log/messages | grep openvpn” to see all of the messages? How did you get these messages?

        • Hi,
          “Additional Config” field is empty. I have no startup script insert. It is a new router which I flashed. I haven´t import any old settings and never used openVpn before. Maybe I used an old guide and copy outdated config files.

          I installed a logserver on my desktop und copied the lines. Now I am at work in another city. I take the router with me an looked in “/var/log/messages” but it is empty 😦

          Can you give me a link where i can find the settings for ” mega – build 21402″ or your settings which work ?

          kind regards, stefan

        • Hi Ben, sry I was some time not at home, So I couldn´t look after the router.
          Can you send me your “Additional Config” / “Server Config”. After i tested different things I think there is my error.

      • mode server
        proto udp
        port 1194
        dev tap0
        auth SHA256
        keepalive 10 120
        verb 5
        dh /tmp/openvpn/dh.pem
        ca /tmp/openvpn/ca.crt
        cert /tmp/openvpn/cert.pem
        key /tmp/openvpn/key.pem

        This is obviously bridged mode. You may not want that. Honestly, you should be reading and following the link I posted above. These settings need to match other router settings and settings you choose for your vpn clients. Copying and pasting my config without knowing what it’s for could do more harm than good.

        • Thanks a lot. I have had adapted the parameters for my conditions and it works fine. Thanks for your patience !!

  33. Great tutorial. Got me up and running with dd-wrt in no time.

    I realize you’re not involved with the development of the firmware, but do you know why this build of dd-wrt (for this router) does not include rflow support? If I’m reading correctly, the “mega” build does have it built in, but there is no option to enable it (under the Services tab).

    • Glad to help 🙂
      I’m afraid I have no idea why rflow is not included – I will have a look on my box later and if it’s available on mine I’ll let you know.

  34. Updated to Merlin, then discovered that all of the dd-wrt links for 64k compatible firmware appear to be dead… Can anyone help with this? maybe repost or e-mail me a build of 21402

  35. Hi

    Cant flash my router running: CFE: and Asuswrt-Merlin – build BETA 1.

    when I try to firmware update to dd-wrt.v24-20979_NEWD_2_K2.6_mega-RT-N66_64K, I just get at message box saying that it is a wrong build/image.


  36. Hello

    Excellent guide. I performed all your steps and everything is ok.

    Just a quick question though.

    Under Space Usage for the NVRAM i have the following:

    28.27 KB / 64 KB

    Is that normal? or didnt i do the 30-30-30 reset right?

    Thanks in advance,

  37. I’m having a problem with this setup right now and I’m hoping you know the answer. When a device connects via DHCP and tries to download a bunch of stuff all at once or in a row (e.g. doing package updates on a Linux computer or updating a bunch of apps via Google Play on an Android phone), the router cuts off the data! They stay connected to the router but cannot reach the internet or even other devices on the network!

    I *think* it’s only for DHCP connections and it *seems* that using a static IP eliminates this issue, but I’m not 100% certain about that yet. Have you noticed this? Is there a setting in DHCP I need to set?

    • Hmm, that is strange.
      I honestly have no idea why that might be happening. If it were me I would do a 30-30-30 reset of the router and just configure the bare minimum. Then try it again. If you cannot reproduce the issue then great! Start re-enabling each of the features (wifi, QoS, Firewall rules etc.) until the issue reappears – at least then you can narrow it down.

      Let us know how you get on.

  38. thanks for the guide! I had only a slight problem with “permission denied” error when I had to run and apply the CFE update via SSH, but chmod +x command helped after I used it on the downloaded and unpacked files.
    Now I have a fully working DD-WRT. Just a note for such beginners like me: after putting DD-WRT on the router, my Firefox did not allow me to do any change in settings in the GUI of the router. Clear history of Firefox, or use it in private mode will solve this problem (kind of authentication bug in Firefox).

    But the best thing is, I have “client” mode now! I can reach a far router what I could not do with my laptop, so finally I have access 🙂
    Thanks for the guide!

    ps.: I have installed “dd-wrt.v24-21402_NEWD_2_K2.6_mega-RT-N66_64K.trx” after the CFE update from the given link:
    Do you recommend using a different one, or this one is ok? Not everything clear, what are the differences between the files in the ftp list. Thanks again!

    • Hi Andreas,
      Glad the guide helped 🙂

      The build you flashed is exactly the one you want. DD-WRT comes in different flavours (see here), the FTP has the builds for all the different flavours for loads of different devices. The mega build is usually the one you want – it has all the features 🙂


  39. Please help I have managed to brick my first router and am now on the second one. Is there a update for hardware version B2 machines? My CFE is and trying hard to find what I require before proceeding to the next steps. Is it just the same? Just upload to the I am using the WinSCP as use novice types do but have no idea where the file tgz should go. Any assistance much appreciated.


    • Hi,

      If you have a second revision of this router please DO NOT USE THIS GUIDE.
      This guide was written for the first hardware variant of the device and so may not work for the B2 version – in fact, it probably won’t work.
      You should look to the DD-WRT forums for more information – I don’t have a B2 unit so I don’t think I can be much help.
      Until your post I was unaware that a second hardware version existed – I will update the guide with a warning.


  40. I’m thinking of upgrading to the Asus RT-N66R or N66U.

    But I’m restricted by only having Uverse DSL max downstream speed of 3 MPS in my area. Would I benefit from upgrading to this router?

    Primary use would be for online gaming and webcam broadcasts. Thanks.

    • Hi Mike,

      In all honesty, using a beast of a router like this will probably not help much if you are having trouble with online gaming. Your internet connection will be the main limiting factor.
      However, this router is fantastic and I recommend it generally. It is especially good if you want to shift data around your house at great speed. I have loads of 1080p videos on a NAS box in my living room and this router does a great job of streaming it to my devices over wifi. This is something that the crappy routers you get from ISPs have no hope of doing.

      Hope that helps,

  41. I’m running the 21402 build and I’m looking to install Snort or TCPDUMP to sniff traffic. How can I go about getting this implemented? Please provide step by step instructions if possible. Thanks!

    • Hi Scott,
      I’m afraid you might struggle with this. To do this you need to install optware. Unfortunately I don’t think anyone has managed to do so on this device. Your best bet is reading up on the topic on the DD-WRT forums.
      If you do manage to do it please let me know how!

      • It turns out that optware isnt compatible with that build. Have you tried the new K3.x builds? I wonder if that had support for optware

        • I’m afraid I haven’t – work is a bit mental right now and pouring over my router for hours on the weekend has low ‘girlfriend approval factor’.
          Let me know if you have any success though 🙂


  42. Could you please update the section “Flashing DD-WRT”. Please note that you need to select the RT-N66_64k.trx (_64k prefix!!)
    Especially because in the latest build 21913 there is not one!! That’s why I accidentely used the dd-wrt.v24-21913_NEWD_2_K2.6_mega-RT-N66.trx
    It bricked my router. Luckily the recovery mode mentioned in some of your comments above worked! In recovery mode I flashed it with build 21402 dd-wrt.v24-21402_NEWD_2_K2.6_mega-RT-N66_64K.trx. Waited for 20min and performed a 30/30/30 reset (with WPS button instead of reset button).
    Hopefully this helps others.

    • Hi Jan,
      Thanks for the info 🙂
      I’m glad you sorted the problem. I have updated the guide accordingly so that others don’t fall into the same trap.


      • Hi Charles,

        I just received the modem in the mail today Jan 15th, 2014. The box will have standard firmware installed. Is your instructions up to date or is there a much easier way of flashing to dd-wrt via Web GUI? I just need to know exactly which files to use and step by step info..Thanks

        • As mentioned at the top of the guide, it is now quite out of date and so should not be followed. My advice is to go to the DD-WRT forums and read about installing one of the K3 builds.

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