From DD-WRT Wiki
 Important Notes
Only version 1 is supported. Versions 2 & 3 are not yet officially supported.
There is an unofficial port of dd-wrt to the version 3 hardware it is discussed in this thread here 
Use only K2.6 builds with nv64k in the name, K3 builds are in Beta!
Read Peacock topic (at top of Broadcom Forum). Read it all. Carefully.
 Hardware Specs
|CPU Speed||480 MHz|
|Flash ROM||8 MB|
|Radios||2.4 GHz and 5 GHz|
|WLAN Max Speed||300 Mbps on 2.4Ghz and 300 Mbps on 5Ghz|
|Switch||4x 100 LAN + 1x 100 WAN|
|USB||1x USB 2.0|
 DD-WRT Installation
- There are two versions of this router with corresponding initial flash mini firmware. One is for Netgear branded routers and the other is for Cablevision routers.
- Do a factory reset (recessed button in the back), and upgrade with the appropriate mini firmware above. If it complains about downgrading, just Allow.
- To gain functionality of the usb port, upgrade to the big version or the mega version after flashing the mini version above.
- 30-30-30 reset router (as described in Peacock).
 Build Notes
- Version dd-wrt.v24-30534_NEWD-2_K2.6_mega-nv64k.bin bricks this router
- Version dd-wrt.v24-28493_NEWD-2_K3.x_mega-nv64k.bin bricks this router
- does not brick this router.
- does not brick this router.
- "You can update to this build however the router may not respond immediately after flashing. Do a 30/30/30 reset after flashing to allow it to boot then power cycling should get it going."
- Use only Mini version of this build! File
- Upgrading to Big will brick this router!
- Mega contains the Heartbleed vulnerability!
- This is otherwise a very good build for this router.
- Recommended build for this router.
- DLNA version (home)
- VPN version (office) (Has been known to brick router)
This router can be "bricked" (rendered inoperable) by flashing the wrong firmware; by not following the correct flashing procedure (in Peacock); or by flashing a bad build like 21676 Big.
 Factory method
 Recovery mode method
This method, which works on the WNDR3800, may also work on the WNDR3400v1.
I tried the recovery method listed for WNDR3800 and couldn't seem to get it to work, it could be the timing. I was trying with linux TFTP and it does try around ten times and started it before and just after starting it but still didn't work.
What does work is a serial recovery, with serial adapter attached here is what worked.
- Hit CTRL-C then start router
- Type TFTPD at CFE prompt to start TFTP server
- Could not get firmware to flash from CFE prompt
- TFTP either the official netgear firmware or DD-WRT initial flash firmware.
- Had to use firmware with ".chk" extension, DD-WRT firmware with ".bin" extensions would flash, however, it would stop there and router will not program.
- Afterwards you can then upgrade to mega or Kong builds.
Gostmn26 15:16, 23 November 2014 (CET)
 Pin short method
- Timing of the pin shorting is tricky -- power on, wait for the lights to flash, then try shorting a few times until the power light starts flashing steadily.
- Next use tftp2 (with no password) to flash factory firmware.
- After the flash, wait at least five minutes after the router boots up and the power light becomes steady green before resetting the router.
Here is another overview of the process for the WNDR3400 http://stevejenkins.com/blog/2014/01/how-to-unbrick-a-netgear-wndr3400-n600-router-after-a-bad-dd-wrt-flash
 Revert to Factory Firmware
- Download official Netgear firmware
- Reset DD-WRT (recessed button in the back)
- Enable telnet under services
- Telnet to router (192.168.1.1)
- Issue the command "mtd erase linux" & wait ~3 mins
- tftp the official firmware to the router
- tftp for windows  enter router ip, leave password blank, select official firmware file
- 30-30-30 reset router (as described in Peacock)