Router DNS not resolving host name temporarily

[Kevlarmpowered]

I have an AC68 and it has been working fine aside from it overheating. I now have a room fan blowing directly at it to keep it cool. Within the past week, I have noticed that DNS has a temporary blackout for a few minutes before starting to work again.

It took me a while to figure it out, but randomly, it seems like DNS decides not to work and will come back with the error, can't resolve host name www.google.com (or your favorite host here). The computers connected to the router all suffer from the same problem and if you run a nslookup on the router itself, it says 127.0.0.1 unable to resolve hostname.

Saturday I updated to the latest firmware to see if it would help... no luck.

 

[ColinTaylor]

It sounds like your upstream DNS servers are not responding. But that might be because you have lost all internet connectivity.

Look in the router's syslog for error messages. But if you're having to cool the router with a fan that might indicate faulty hardware.

 

[Kevlarmpowered]

I've tried different DNSs from Google DNS, to OpenDNS to even my ISPs provided (Comcast) DNS. Same problems. I originally thought it was a loss of connectivity... but Comcast can see into their equipment during these issues. That is when I started to isolate the problem to the router... the router is old which makes me think it could be it. I just don't want to drop $250 on a new router without making sure I eliminate all other free solutions.

 

[ColinTaylor]

As I said, look in the syslog for any error messages. Also, when you have the DNS problem check to see whether you have connectivity to the servers.

ping 8.8.8.8

 

[st3v3n]

Gents, I ran across your thread and it seemed related to things I've been dealing with. My RT-AC3200 hasn't been entirely well-behaved since I upgraded from FW 380.68 to 380.68_4. What you wrote about DNS and nslookups, went along the lines that I've been experiencing, (without the GUI stalling and/or crashing I've had). The DNS was failing when I had to drop to WAN, when working with the client configs. Today NTP just stopped; the pool wasn't responding, though the tunnel kept trying to work for a minute of so it seemed. The config usually takes care of everything unless I have to work over WAN when the client isn't up.

The logs indicated the router was stuck, eternally waiting for a nts update that never arrived. Without time and DNS the client finally dropped. I've been testing without any resolution for days. I turned STP off, saved, rebooted, then changed to GMT and a tier one server, saved, rebooted again. Then I reset the beginning/end dates for DST, saved and loaded a new config. That finally seemed to do the trick. Whatever the problems were, so far the router hasn't exhibited further issues re DNS/time and the tunnel is working normally. The GUI is still very sluggish but it hasn't crashed outright again. Your thread and a couple semi-related posts helped jar a spare thought loose, I was ready put the backup router in service.

 

[Kevlarmpowered]

The AC68 was replaced with an AC3100 this afternoon... let's see if the problem persists. It likely had something to do with the age of the router. High temps likely just took its toll on it and it finally gave up.

If the AC3100 has the same problems, then I'll know the problem was someplace else, but I got tired of the non-stop phone calls of. I can't work because there is no internet.

 

[st3v3n]

Kevlarmpowered, I stopped QoS, opened bandwidth to the max, both up and down, cut back logs to error only; the RT-AC3200 has run all day without lagging or dropping, so maybe I dodged a bullet. I think I'll set a laptop cooler underneath it tomorrow see if it drops the temps a bitmore. My 8-core CPU runs as cool or better, but then it does have a water-cooler. Be a trick to put one of those on the router. Good luck.

 

[Kevlarmpowered]

I've read stories about the heat sink separates from the chips... I think mine must have done just that. It was fine for years and then one day it was acting up and I noticed the temps were higher than normal, so I put a desk fan next to it and the problem went away for a while. Then it started happening again and I just replaced it with the AC3100. When I unplugged the AC68 before getting ready to punt it into the recycle bin, the CPU temp was registering 64C. The new AC3100 is sitting in the same place, no desk fan and no problems thus far.

 

[st3v3n]

Kevlarmpowered,I've seen how others resolved similar, high temp issues, i.e., https://www.snbforums.com/threads/9-router-cooling-rt-ac68u-example.26733/ (Aug 21, 2015 #1), and photos, https://www.snbforums.com/attachments/ac68u_cooling-jpg.4409/

I use a small desk fan, blowing toward the bottom of our AC3200; both router feet and fan are isolated from the shelf with foam pads to avoid vibration. I've utilized 200mm fans for other high-value cooling projects. I fixed high temps in an automated studio mixer where vent cooling didn't help, but mounint a 200mm fan to the bottom to draw air through it, did. I think I'll order another 200mm fan for the 3200, that should keep it cool enough. I'll either wall-mount the 3200, with the bottom of the router facing the wall, with stand-off space for cables and good air flow, or use a couple of small shelf brackets, with the router sitting normall and the fan directed up from underneath.

I'll probably use the $20-$30 Noctua NF-A20. I don't like cheap fans for cooling expensive gear. The router doesn't need the expense of liquid cooling, though I'm sure someone's done it. Noctua fans are silent, without vibration and enjoy long life. I clean the dust off the router and fan, and blow it out every month. I saw a youtube video of a fellow's router-shelf, mounted 7 feet above the floor, where he used a couple of multi-colored LED fans blowing up. While you might gain some Wi-Fi transmission area, the higher it's mounted, higher ambient air temps offset the fan cooling.

If something like this doesn't lower your temps, a tear-down is in your future to check the CPU/heatsink status. Good luck.

 

[Kevlarmpowered]

I owe you guys an update...

Disconnection issues continue, however they don't seem to be nearly as bad. Where I used to get multiple disconnects a day, I typically only get one or two now (that I am aware of) and they don't last as long. I've been on the phone with Comcast and they tell them to call them back when the disconnection occurs, however by the time I get through their stupid phone system, the connection problem has normally resolved itself ... and they are very quick to blame my home connection equipment instead of theirs.

@st3v3n

In regards to cooling... I had a massive room fan blowing directly at the vents of the router. The fan was probably 400mm in size. I used to have the fan directly under the unit blowing throw it but I found it interfered with the wireless range so I moved the fan about a 1ft a way pointed towards the back of the unit and that used to help.

 

[st3v3n]

Kevlarmpowered, I once tried a laptop cooler under our 3200, that had a high volume, low speed fan and was silent. It kept the 3200 cool enough but didn't play well with the Wi-Fi, so I had to go back to the side flow fan. With a good quality, ie Noctua or other quality fan, that doesn't sqawk RFI everywhere, results should be much different. I'll check back after getting a new fan to test. Imagine the router with the bottom facing the wall, but an inch/two away, with a fan or two in foot below, blowing up. That's what I saw in a frame. As long as a cat doesn't climb up there, or kiddies can stick their fingers in..

Are your time lookups still problematic? Is your DST accurate, automatic and ready for next week-end? Depending if Comcast requires you to appear to them from WAN, if their DNS is faster than google, and privacy isn't at stake, they have a vested interest in getting to the bottom of the dropouts. As for our ISP, their interest stops at our modem; we bought it, we let them manage it if need be. We keep our traffic private using openvpn, don't cause them a headache or misbehave, and we're all relatively happy. That's sort of what the intenet was intended to be. Still, I expect a couple of client drops per day if I run outside of an openvpn tunnel.

If you aren't required to show Comcast a domain name or use their DNS, you can try the DNS tool at GRC.com to see what the fastest DNS would be for you. Google usually does well, but so does 4.2.2.1 and others. If you pay for OpenDNS, Comcast should have no problem with them and hold out for better, faster troubleshooting this problem. They shouldn't hold you on hold forever, and if you use their servers, surely they can send a tech out to help if this doesn't resolve.

Most devices fetch if from the LAN DHCP server from the router, some allow you to manually list DNS, like iphones and ipads. If Comcast's DNS servers are fast enough, and privacy isn't an issue, then pester them politely and persistently. A couple devices we have refuse to look at any DNS that doesn't have an 8.8.8.8 attached below it somewhere. With a windows PC you have several choices how to show the DNS you want, and usually works autmatically quite well. If VPN traffic isn't at stake, pardon me, I've barked needlessly at trees. Hope this helps, cheers.