From DD-WRT Wiki
 Hardware Specifications
|CPU Speed||480 MHz|
|Flash ROM|| 16 MB|
|Radios||2.4 GHz, 5 GHz|
|WLAN Max Speed||300mbps (2.4 GHz) & 450mbps (5 GHz)|
|Antenna Location||Internal (x6)|
|Bands||3 x 3|
|Switch|| 4x GigE + 1 WAN|
|USB||1x USB 2.0|
Radio wl0 is Broadcom 4718 (SoC)
Radio wl1 is Broadcom 4331 Intensi-fi Single-Chip 802.11n Transceiver
 These instructions are for E4200 version 1 ONLY! Version 2 has a marvel chipset and is NOT supported
- The E4200 is very sensitive to the nvram size.
- For the initial flash, upgrading stock firmware to DD_WRT, use Flashing process procedure below! Please follow it. To prevent a brick use only trailed builds.
- A trailed build has "E4200" in its name like: dd-wrt.v24-18777_NEWD-2_K2.6_mini-e4200.bin
- The only safe builds which can be used AFTER initial flash for this router are nv60 builds.
- NV60 build has a name like: dd-wrt.v24-18777_NEWD-2_K2.6_big-nv60.bin
- Recovery from a firmware with the wrong nvram size requires use of a jtag cable to erase the nvram.1
- Support for the E4200 is still very much a work in progress at this time, outstanding issues reported have included WAN stability, and both 2.4GHz and 5GHz Radio stability. The E4200 works very well with Kong 22000++ (see below).
- The E4200 dissipates a good deal of heat at the stock 100 mW transmit power. Ensure adequate cooling or reduce transmit power to 40-50 mW.
 Flashing Process
Perform these steps for initial DD-WRT flash from the stock Linksys GUI:
- Read all required reading sections of the peacock announcement.
- Disconnect any Ethernet cables from router and PC, and disable PC wireless.
- Do a Hard reset or 30/30/30 of the router.
- Connect Ethernet cable from a LAN port (not the Internet port) of the router to PC doing the flash.
- Wait for router to boot up, and then for PC to get DHCP address from the router.
- Open router GUI (192.168.1.1) in Web browser on PC.
- Flash an E4200-specific mini build; e.g., 21676 trailed initial flash build for E4200
- Do NOT use a build with "nv60k" in the name for the initial flash; use only the trialed build linked just above.
- 21676 is a stable, reliable, recommended build for the E4200, but only use the mini version, since larger versions have the dangerous Heartbleed vulnerability. If you need more functionality than mini, upgrade to Kong 22000++:
- Wait for flashing process to complete, then wait 3 more minutes.
- Perform a Hard reset or 30/30/30 after the device has successfully updated.
- Wait for router to boot up, then log into DD-WRT Web interface (192.168.1.1).
- You may have to clear your browser cache before the Web login will display.
 Upgrading Process
- If you need to upgrade to a build other then mini or a newer release take note of the following.
- If a nv60 build is flashed to the router those are the only builds which can be flashed from that point on.
WARNING AFTER installing DD_WRT, ONLY flash -nv60k builds,
Flashing anything else to the router will brick it as noted above
- Select the build of your choosing (Mega, Big, std_usb_nas, OpenVPN, VoIP).
The E4200 works very well with Kong 22000++.
- Follow the same flashing procedure as you used for the initial flash
 Reverting back to stock firmware
- You can always revert back to stock firmware.
- Download the latest E4200 firmware from linksys site.
- Disconnect all cables and wireless clients.
- Perform a 30/30/30 reset on the device.
- Login and select the stock firmware file and flash, make sure to select "reset to defaults" on the drop down menu when flashing.
- Wait approximately 5 minutes for the flashing process to complete.
- Perform a 30/30/30 after the device has successfully updated.
 Wireless-N Configuration
- As is explained in Wireless-N Configuration make sure that you use AES with WPA2 security for your wireless N network. Do not use TKIP or the wireless speed will revert to the g standard and that would be a pity. (AES+TKIP is also allowed but not recommended.)
- It is recommended to set:
- 2.4 GHz radio to "NG-Mixed".
- 5 GHz radio to "NA-Mixed".
- Both 2.4 and 5 GHz Radios run at a stock transmitting power of 100mW. Decreasing the transmitting power to a value between 40 & 50mW may help stability, especially if the router has poor cooling.