Asus RT-N66U

From DD-WRT Wiki

Jump to: navigation, search


[edit] Hardware Specifications

CPU Broadcom 4706 @ 600MHz
Flash/RAM 32MB / 256MB
Wireless support 2.4GHz and 5GHz bands
Wireless controller Broadcom BCM4331
MIMO config 3x3 (both bands) (see Ref: forum)
ETH chip Broadcom BCM4706
Switch Broadcom BCM53125
Ports Gigabit LAN (4) and WAN (1)
USB 2x USB 2.0
Other Micro SDHC socket (internal)
Power supply DC Output, 19 V, max. 1.58 A current (=> max 30W)
Serial header 8, n, 1, no flow control, 115200.

[edit] Installation Instructions

Read the Firmware FAQ, Peacock Announcement, new build, and model-specific threads.
WARNING: This 'Dark Night' presents significant risk to bricking that requires careful adherence to the installation process, however, there is a built-in and robust Recovery Mode.
NOTE: The NVRAM issue has been resolved in newer CFE versions (and K3X builds).
NOTE: It is highly recommended to use Private, Incognito, InPrivate browsing mode with no extensions or add-ons enabled, and no passwords saved to the browser in any way when flashing or accessing the webUI. It is preferred to use a Portable browser such as Firefox, Firefox ESR, or Pale Moon. If you run into issues, clear browser cache or override with CTRL+F5

[edit] Preparation

  • If upgrading to DD-WRT from other firmwares, then use a *.trx file, as in *_RT-N66U.trx file for initial flash and upgrades, or only half the memory will be available (with ASUS routers, using a *.trx file is always a safe bet).
  • If you are upgrading from one version of DD-WRT to a different (newer/older) version of DD-WRT, you can also use the firmwares that end in *.bin. as in _mega.bin or _big.bin
  • IMPORTANT: Determine what version of CFE you have on your router, if CFE v1.0.1.3 (64K nvram) or 'NEWER' - DO NOT USE K2.6 builds
  • If using Older CFE (32K nvram) you can use K2.6 builds
  • Reset BEFORE and AFTER firmware upload. If upgrading from DD-WRT to a newer version of DD-WRT, then before is (mainly) optional.
  • Refer to the Notes section below if any of the following steps are confusing
[edit] Upload via Web GUI
  1. Reset NVRAM via WPS button , or select WebGUI option: Factory Default settings.
  2. Upload the DD-WRT build using the stock web GUI (use file ending in .trx or .bin, according to description under Preparation).
  3. Wait until the router reboots itself, which can take at least 10 minutes (some times 30 minutes or more). Be patient and wait until you get a response from both ping and the routers WebGUI when you use your PC to access the router.
  4. Reset NVRAM via WPS button, or select WebGUI option: Factory Default settings. Wait for the router to reboot!!

Note: If you are having trouble uploading a newer version of DD-WRT, using the WebGUI, then you might want to try to use a different browser. Sometimes it solves the problem.

[edit] Upload via ASUS Recovery Utility
  1. Set your computer to a static IP (e.g., 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 Asus CFE recovery mode by issuing in browser field.
  4. Browse to select the DD-WRT trailed build (N66U big or mega .trx) then click Upload.
  5. Wait until the router reboots itself, which can take at least 10 minutes.
  6. If it doesn't reboot after 30 minutes, power off for 10 seconds, then reset via WPS
  7. Reset (via WPS) or reenter recovery mode and select to Restore defaults NVRAM values
  8. Wait until the router reboots itself, then access the DD-WRT GUI at to set a password.
[edit] Switching from Tomato
  1. Navigate to the Tomato firmware update page
    • Administration -> Upgrade
  2. Upload the firmware you downloaded in step 1
  3. The router will reset several times and change its IP address to the default one (
  4. Navigate to
    • The login credentials have been reset to the default dd-wrt username/password (root/admin)
  5. Set "Restore Factory Defaults" to yes and click "Apply Settings"
  6. After reboot, set a new user/password
Note: Reset to factory defaults after flashing from Tomato to DD-WRT to avoid undesired behavior and instability.

[edit] Upgrade to newer DD-WRT

[edit] Revert to original ASUS firmware

  1. Download firmware from ASUS web site
  2. Reset to Factory Default Settings or clear NVRAM
  3. Use the DD-WRT web gui: 'Administration -> Firmware upgrade', to upload the ASUS firmware file you downloaded in step 1.
  4. Reset to Factory Default Settings or clear NVRAM

[edit] Mods

[edit] Internal MicroSD card

The N66U has an unused internal MicroSD card slot, but note that USB (and thus MMC) is not supported on K2.6 builds. However, it is working on K3.x builds. See SVN ticket

  1. Open the case
    • Unscrew the four screws at the bottom
    • Then you want to release the plastic clips that holds the top and bottom parts together.
    • Pry the bottom case outward, which has the male clips.
    • For future access, it is recommended to either snip off the female "U" clips on the top cover, or round off the square edges on the male part of the clip with a nail file.
  2. Install MicroSD card
  3. Enable USB features to utilize the MicroSD card

For easier access, see below.

[edit] Case Top Mod

Spacers (~1/4" to 10mm) can be installed to elevate the case top, which allows easier access to the MicroSD card, and also improve cooling. A piece of dark foam and hole punch can be used to retain the top cover LED lighting.

[edit] Overclocking

Overclocking works since CFE, while underclocking worked prior to that. Overclocking may cause instability, or services (like QoS) to behave unpredictably

  • Recommended to improve cooling or ventilation when overclocking, like the case top mod
  • jwh7 has run @663MHz (CFE without issue for 3 years, with an elevated case top
  • There is one report of QoS degradation at 632Mhz with K3.X big r27360 (06/18/15)

[edit] Power Consumption

Asus RT-N66U (measured with a kill-a-watt meter that has 0.000 resolution)

  • PSU default numbers: 19V, 1.58A => max 30W, so there is also power for any USB devices.
  • PSU standby usage: 0.06W (only the PSU is plugged in, no Router is connected)
  • Unit running idle: 9.8W (Radio enabled, but no network cables in LAN or WAN ports)
  • Network cables connected: 10.6W (Radio enabled, and wires connected to WAN port and 1 LAN port)
  • 2.4GHz Radio usage: 0.9W (difference with 2.4GHz Radio On or Off)
  • 5GHz Radio usage: 1.5W (difference with 5GHz Radio On or Off)

[edit] Notes

[edit] Reset button for Recovery

Pressing the Reset button (labeled like ' > o < ') at powerup will put the N66U into recovery mode.

  • Press and hold the reset button then plug in power until the power LED starts blinking. Access recovery mode at

[edit] WPS button to Clear NVRAM

Pressing the WPS button at powerup will reset (clear NVRAM) to default settings.

  • Press and hold the WPS button while plugging in the power for about ten seconds. All the LEDs should flash, indicating settings have been reset to default settings.

[edit] NVRAM issue

IMPORTANT: DO NOT USE K2.6 builds if using CFE v1.0.1.3 (64K nvram) or NEWER!!!
At launch, the RT-N66U was limited to 32k nvram. However, CFE (bootloader) version added 64k nvram support around April 2013, but was not compatible with DD-WRT firmware at that time. For details, see these forum links to historical nvram and 64K implemention discussions: Fractal comments and "RT-N66 CFE Thread"

This was resolved with DD-WRT K3X builds (kernel 3.x) which extended nvram to 64k, and can be used for any CFE version. It was eventually extended to 256k.

More historical info:

For newer CFE version updates and procedures see here: SNB Forums

Note: CFE is a bootloader for routers. The CFE is what loads the firmware when using ASUS Recovery Utility (and/or a TFTP tool)

NOTE: Why does the wiki not state to use the K26 nv64k upgrade images with the updated CFE? -kp69

[edit] CFE Version (or Update)

AsusWRT-Merlin can be installed to enable telnet/ssh. telnet/ssh can then be used to check the CFE version as well as update the CFE version. DD-WRT can then be flashed directly from Asuswrt-Merlin

Find the CFE version:

  • in telnet/ssh type: nvram get bl_version or strings /dev/mtd0ro | grep bl_ver

To update the CFE version:

[edit] K3.X Builds

Note: do NOT use build 40559 - 40559 is broken for most routers, despite being the recommended build for many routers in the Router Database. Search forum "New build" to get the latest updated info about builds (noted Aug 2020).

[edit] K2.6 Builds

USB (and thus MMC) also does not work in K2.6 builds. USB devices cause a kernel panic: see SVN ticket. Use a K3.x build (see above), which also works around the NVRAM issue.

NOTE: All K2.6 builds between 43136 and 44112 are broken. REF

[edit] DD-WRT Alternatives

User Merlin implemented a solution in mid-2012 to extend the original 32k NVRAM CFE to ~60k NVRAM in firmware

TomatoUSB Shibby also implemented a 64k NVRAM solution for 32K NVRAM CFE in 2012.

FreshTomato also supports this device and includes the 64K nvram solution from Shibby.

[edit] Historical Build Information

This is only potentially relevant if using builds from 2015 and earlier.

  • If already running a custom 64K Build like Fractal or Kong with CFE, 26138 mega nv64k must be used to upgrade. Since K2.6 Builds have an embedded check, you need to use those special nvXXk trailed images. On K3.X this check has been removed and you can simply upgrade from a previous K3.X.
  • With K3.X Broadcom builds, the CFE version is less concerning since DD-WRT detects it automatically to extend the 32KB limitation.
  • Build 24461 BRICKS the RT-N66U, but recover is possible through the mini CFE web interface.

[edit] Performance

Test Description                                 RT-N66U
WAN - LAN	                                 732 Mbps
LAN - WAN                                         729 Mbps
Total Simultaneous                              810 Mbps
Maximum Simultaneous Connections   34,925
Firmware Version                        (stock firmware number)

Sources and testing methods

[edit] LAN/WAN issue

There should be no vlan0ports in nvram for the N66U switch: [1] and [2]

[edit] Links

Primary forum threads

Additional forum threads