Sunday, October 7, 2018

Unbricking My TRENDnet TEW-812DRU Wireless Router

Upgrading my TRENDnet TEW-812DRU v2 router with DD-WRT firmware sometimes goes smoothly, and sometimes not. Usually if the upgrade fails on the first try, I can just unplug the router, wait 10 seconds, plug it in again, wait for the web UI to come up again, re-upload the firmware (and wait), and the upgrade will work on the second try.

But sometimes the router won't boot up correctly. All the blinking lights come on as normal, but it doesn't do any actual routing — or provide any DHCP services, which makes the router look bricked, even for devices connected to it physically with an ethernet cord.

But fortunately, it's not actually bricked. The router still grabs its usual local address (, if you haven't configured it to be something else), and runs its nifty "TRENDnet - Emergency miniWeb Server" on port 80. The emergency page served up allows you to upload a new firmware image — and every time (so far) that I've gotten to that page, I've simply been able to upload the firmware image I've been trying to install (ie the latest trendnet-812dru-webflash.bin file from DD-WRT); and the router accepts it, installs it, and reboots itself, and everything is back to normal and happy in a few minutes.

The trick to accessing the router when its usual networking services are down is to 1) connect a computer to the router via wired ethernet connection (if you don't have one set up that way already), and 2) configure that computer with a static IP on the router's local subnet.

Since I'm running my router at, I just set the computer's static IP address to, and point its browser to The emergency web server seems to listen only for a minute or two after booting, though, and then goes way; so if the emergency page won't load, I unplug the router, wait 10 seconds, and plug it in again.

And since that wired computer is running Ubuntu 16.04 (with a wired interface named enp1s2f3 — look it up via a command like ifconfig or ip address etc), I set its static IP address by adding the following to my /etc/network/interfaces:

iface enp1s2f3 inet static address netmask gateway dns-nameservers

And then run sudo service network-manager stop to make NetworkManager cool its butt, and sudo service networking restart to use the static IP.