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How To Install DD-WRT On Cox Netgear R6300v2

Firmware flashing guide for the COX ISP variant of the Netgear R6300v2 AC1750 router. Disassembly, serial TFTP flashing, and initial DD-WRT flash.

Netgear r6300v2 router, cox variant

The Netgear R6300v2 is a very capable 802.11ac wireless router. It can be found on sites like for less than $50, making it an affordable choice for upgrading from an old 802.11a/b/n router.

And best of all: it supports custom firmware, providing a better web interface and unlocking features not found on the stock netgear firmware.

There is a gotcha though. There are three variants of the R6300v2 router, the original by netgear and two ISP branded variants. The other two variants are very easy to flash custom firmware to, but the Cox ISP variant has some extra hoops to jump through to get DD-WRT loaded.

This is a comprehensive guide to loading DD-WRT on a Cox ISP variant Netgear R6300v2 from stock.

Parts and Tools

  • Torx screwdriver set
  • Soldering Iron (and solder)
  • Pin Header This one from sparkfun should work well. If you don't have or want to buy the header, you can solder wires directly, but I don't recommend leaving them attached after all is said and done. The header makes it a breeze to attach serial if you ever need to unbrick the router down the line.
  • USB TTL Serial Adapter. Get one that supports 3v3 (3.3 volts). Adapters with a 3v3 / 5v switch work great.
  • PC. Must have an ethernet port. This guide assumes a PC running Windows 10. Instructions for linux and mac will differ.

Download Required Software

We need three pieces of software: the first two being stock firmware and tftp2. Download tftp2.exe, which is a tool to upload firmware to our router and Netgear Firmware:

Download tftp2 here (Google Drive)

Download Netgear firmware here (Netgear.com)

Next we need the latest DD-WRT firmware. First, we head into DD-WRT's repository of firmware downloads:

https://download1.dd-wrt.com/dd-wrtv2/downloads/betas/

Click the current year, then on the next page, scroll down and click the newest date. You should now be on a page with a list of routers, scroll down to netgear-r6300v2 and click that. Download "factory-to-dd-wrt.chk".

Make sure you click netgear-r6300v2 and not netgear-r6300.

Identifying Cox Variant

To positively identify a Cox variant, log into the netgear web interface. In the top right corner, Cox units have a firmware version ending with "COX"

Cox branded units have a firmware version that ends with cox (top right).
Top: Cox branded units have a firmware version that ends in "cox" (top right of screen)

Netgear r6300v2 router, cox variant
Top: Cox branded units have a blue accent along the bottom edge on the front of the router.

Opening The Unit

We need access to the diagnostic serial port on the router's mainboard, so we need to open up the unit.

  1. Begin by removing the three Torx screws on the bottom of the unit. ONE OF THE SCREWS MAY BE UNDER A WARRANTY TAMPER STICKER, PROCEED AT OWN RISK.
  2. With the screws removed, pry on the plastic front plate of the unit, being careful not to damage the clips that hold it in.
  3. With the mainboard now visible, carefully lift it up (its held in place with some plastic pegs protruding from the case), taking care not to yank on the antenna wires and flip the board upside down.

With this, we can move on to the next step.

Netgear r6300v2 with the front plate removed
Top: Netgear r6300v2 with the front plate removed

Netgear r6300v2 with front plate removed and board flipped
Top: Netgear r6300v2 with front plate removed and board flipped. Take care not to pull on or damage the delicate antenna wires (wires on top side of the board).

Serial Hookup

Next we need to locate and connect our USB TTL serial adapter. Locate the serial connector pads on the mainboard. It is located near the Board ID (U12H240T33) label on the mainboard. A smal label "J252" is located directly below one of the serial pins.

Solder a pin header to the serial header's pads on the mainbaord.

Netgear R6300v2 serial connector
Netgear r6300v2 mainboard serial connector pads with headers soldered. It is located near the Board ID label and has a tiny "J252" label directly under one of the pins.

Next we hookup our USB TTL serial adapter to the pads.

The order of the serial header starting from the "J252" label on the board is:

[J252]
[Receive][Transmit][Ground][Not Connected]

Attach your serial adapter to the header. If your adapter has a 3v3 / 5v switch, make sure it is set to 3v3. Connect receive (rx), transmit (tx) and ground (gnd).

Don't Connect The Positive Wire

Do not connect VCC (+V, +5v, +3v3, Pwr). Doing so may cause the router to behave irratically or worse.

USB to serial ttl adapter
A USB to Serial TTL adapter.

Plug the adapter into your computer. If you've never used the adapter before, Windows should automatically install a driver for you.

Finally, we need to find out which COM port Windows selected for our adapter. Hit Windows+R on your keyboard, type "devmgmt.msc" no quotes into the textbox, then hit enter. Scroll down to ports and you should see an entry like "USB Serial Port (COM4).

Finding a COM port in Windows Device Manager (DEVMGMT.MSC)
Finding a COM port in Windows Device Manager (devmgmt.msc)

Take note of the assigned COM port, we'll need it in the next step.

Test Serial Connection

Now that serial is hooked up, we need some software to view the serial console. For that, we need some software, PuTTY.

The PuTTY windows installer can be found here.  Download and run the installer. Then run PuTTY.

Under Serial Line, enter the COM port assigned to your adapter. Set speed to 115200. Click open to launch the serial terminal session. Now plug your router into power and switch it on.

Putty configuration settings example
PuTTY configuration settings. Replace COM4 with whatever your COM port is.

If you did it correctly, PuTTY should now begin spitting out messages from the router. If you get garbled text, check that the speed is correct or try swapping the Receive and Transmit wires with each other.

If your USB to Serial adapter gets disconnected from your computer, you will need to start a new PuTTY session.

Get To CFE Prompt

Next, we need to get to the CFE prompt, where we will run our commands.

Start by rebooting the router. As soon as new text starts being displayed in PuTTY, start pressing CONTROL+C on your keyboard repeatedly. Assuming you were successful, you should see:

CFE>

If you see something about "busybox", you've missed the CFE prompt activation window. In this case, power the router off / on again, and try again.

Burn Stock Board ID

Make sure you have a Cox variant Netgear R6300v2!

Flashing the wrong boardid may prevent you from installing/updating the firmware! Or even brick the router!

The main purpose of us connecting serial and getting into the CFE prompt is so we change the Board ID. In order to succesfully flash the stock Netgear firmware, the firmware must see the correct Board ID, otherwise the flash will fail.

At the CFE prompt type in:

burnboardid U12H240T00_NETGEAR

If you don't get an error, then the burning was successful. Reboot the router, get back to the CFE prompt and move onto the next step.

Setup Network Settings

Open the Windows Start Menu, type "network connections" no quotes, then press enter. Right click the ethernet adapter you will be using (usually just called "Ethernet") and click properties.

Windows network adapters page

Double click "Internet Protocol Version 4 (TCP/IPv4)"

Adapter properties

Here we will manually set our network connection settings. Click "Use the following IP address" and enter the following settings:
IP Address: 192.168.1.2
Subnet mask: 255.255.255.0
Default gateway: 192.168.1.1

You can also set the DNS server addresses, but this is not required:
Preferred DNS server: 1.1.1.1
Alternate DNS server: 8.8.8.8
This tells Windows to use Cloudflare DNS, and Google DNS as a backup.

Click OK to confirm settings.

Network adapter IPv4 settings

When you're done with this tutorial, remember to set these settings back to "Obtain an IP address automatically" and (if you don't want to use Cloudflare DNS or didn't set a DNS)  "Use the following DNS server addresses".

Flash Stock Firmware

At the CFE prompt type in:

tftpd

This enables a simple file upload mechanism by which we can upload our new stock firmware.

Open tftp2.exe. Upgrade the "..." button next to the right of the file textbox. Select the stock firmware that was downloaded earlier. Set the program to retry 99 times, then click Upgrade.

tftp2 configuration

A progress bar should then appear and stock firmware should begin uploading to the router.

When it is complete, close tftpd immediately (or it may start uploading the firmware again!) and reboot the router.

You should now revert the network settings we changed earlier, by setting them back to "Obtain an IP address automatically" and (if you don't want to use Cloudflare DNS or didn't set a DNS)  "Use the following DNS server addresses".

Flash DD-WRT

At this point we should now be on the stock variant Netgear firmware. We confirm this by logging into the router web interface and checking the firmware version in the top right. A firmware version without "cox" at the end confirms a successful variant change.

A cox branded netgear r6300v2 flashed with the stock Netgear firmware.
A cox branded netgear r6300v2 flashed with the stock Netgear firmware.

We are now ready to flash DD-WRT.

In the router web interface, click the Advanced tab at the top of the screen. At the menu on the left side, click Administration. Finally, click Router Update. Now, click browse and select the factory-to-dd-wrt.chk we downloaded earlier. Finally, click upgrade.

You may get a warning about the firmware version being the same as the one currently installed. Click yes.

Netgear r6300v2 flashing page

Firmware will now upload and install. When completed, the router will reboot and when it comes back up, it will be on the DD-WRT web interface. The router reboot may take some time, if you get no connection error page, wait a minute and try again.

Conclusion

Congratuations, you are now on DD-WRT. This tutorial is already very long, so it won't go into the details about setting up your router on DD-WRT (there are many good articles out there for that.)

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