A few weeks ago I began to have a recurring and incredibly frustrating problem with my Internet connection. Multiple times a day my Internet connection would drop for a couple of minutes at a time. My cable modem would show I had a good link. Upon checking my ASUS RT-N66U router I would see this in the system log:

WAN Connection: Ethernet link down.

Then a few minutes later the connection would come back on its own. I would see this in the log:

WAN Connection: Ethernet link up.

I work from home, mostly using SSH to log into remote servers. My connection would flake out just long enough for my SSH connection to drop. It drove me up the wall.

I did a lot of Google searching and couldn’t find much of anything about the problem. What I did find wasn’t productive.

Going strictly off of the error message I figured I had one of three problems, bad network cable between the router and modem, bad WAN port on the router, or bad WAN port on the modem. I changed network cables with no luck. I replaced my ASUS router with an old Netgear router I had. The problem stopped. I went back to the old cable, still no problem. I put the ASUS router back into play, the problem started again. I knew it had to be something with the ASUS router. I had owned it for too long to send it back for warranty coverage. I also thought it odd that the hardware in the WAN port could be flakey enough to cause an intermittent problem like this while otherwise working fine. I figured it was software related.

In order to simplify things I turned off every feature of the router I didn’t %100 need. Guest wifi network, QoS,  USB support, DDNS, cloud support, and so on and so forth were turned off. I even shut down the second access point I have in my house. After simplifying everything something wonderful happened. The problem stopped. I gave it a few days to be certain and sure enough, no more drops.

I then began to turn on each service again, one per day. When I turned on DDNS via no-ip.com the drops started again within a few hours. I turned off DDNS and the drops stopped. The culprit had been found.

I don’t have a good idea why the DDNS client causes the WAN Ethernet port to drop out. Its some sort of bug in the 3.0.0.4.376_1071 firmware I’m running.

In the end my solution was to leave DDNS turned off in the router and then to install a no-ip.com update client on my computer.

TL;DR

My ASUS RT-N66U router started dropping my Internet connection. It had something to do with updating no-ip.com. Turning off the DDNS client solved the problem.

Update 9/10/14: I switch to the Merlin Firmware and even with DDNS turned on the router has been fine with no drops. That aside the new firmware is working great, all of the features I would expect and I have not noticed any change in my speed.

Update 5/3/16: I’m still running the Merlin Firmware, updating it as they become available. No problems at all.