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things I break/fix for fun and learning

Jul 7, 2018 - 3 minute read - Comments

OpenWRT 18.06 for WDR3500

I have been testing the upcoming OpenWRT 18.06 RC-1 firmware on my backup WDR3600 router and so far so good. For my weekend project, I have decided to upgrade my main router WDR3500 to use the latest OpenWRT release 18.06. Instead of RC-1, I will use the latest snapshot build. I will also flash it to use a modified bootloader just like my WDR3600, so that I can easily recover from bricks without the need for JTAGs, making this router unbrickable!

Steps to install u-boot mod (credits to pepe2k)

1 - Download the archive located in https://github.com/pepe2k/u-boot_mod/releases/tag/2014-11-19

2 - Extract the archive using tar. Navigate and look for the OpenWRT prebuilt images. Make sure the router model is listed. If it is not listed, do not proceed. For this router, I will be using the prebuilt packages for WDR3500.

3 - Login to the GUI of the router (usually and flash the appropriate prebuilt image. Once completed, the router will reboot automatically.

4 - Telnet / ssh to the router. Once logged in, execute the command u-boot-upgrade. READ and follow the prompts carefully. Once completed, reboot the router.

5 - To access the embedded web server - Turn off the router. While OFF, hold the RESET button and press the power button. LEDS will flash, release the RESET button after 3 secs or after the LEDS has flashed for 3x. This is tricky and needs practice!

Upgrading the prebuilt images to the latest OpenWRT release 18.06 snapshot

The prebuilt images are OLD, they are from Barrier Breaker release of OpenWRT. If my version number is correct, it is version 14, while the latest stable version is at 17 and the upcoming new version is at 18! It is 4 version behind and indeed it is OLD!

The prebuilt images does not contain a web interface. To be able to flash new version of OpenWRT, we can either use the embedded webserver of the modified bootloader or login via telnet / ssh and flash from there via mtd command. I tried to use the embedded webserver but I can’t get the correct timing to access the embedded webserver. In the end, I just transferred the firmware via scp and login to the router. From there, issue the mtd command to perform the firmware upgrade -

mtd -r name_of_firmware.bin firmware

Once completed, the router will automatically reboot and use the new firmware.

Here it is, latest snapshot side by side with RC-1. We can easily see that the newest snapshot uses kernel 4.9.110 while the latest RC-1 uses 4.9.109.

One of the main reason to upgrade the firmware of the router is that it somehow gives protection on the KRACK (Key Reinstallation attack) WPA protocol vulnerability. TPLink does not provide updates anymore for this particular model, but thankfully by flashing OpenWRT, this device gets software updates and becomes better compared to the default TPLink firmware.

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