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Basically, after anywhere from 5-60 minutes, DNS queries fail for a few minutes, then slowly begin to resolve correctly. Then the cycle repeats. This occurs only when more than one computer is on the network. All computers on the network experience the same sporadic DNS outage at the same time.

Wireless or wired, Linux or Windows, fresh OS install or old, browser or ping, same symptoms. Duplicated on 3 routers (not chained together, mind you) and 3 ISP's and 3 separate locations over the past several months. The only common theme is a single 5 years old WIN XP laptop which has been in use on the network throught all this. There also may be anywhere between 1 - 10 devices hooked up wired or wirelessly at a time. The only reprieve I have from this torture is by using any VPN to an outside source - always smooth sailing.

I typically set up any router to

  • use WPA2/etc security
  • MAC whitelist
  • UPNP OFF (if available)
  • always update firmware when available
  • obtain DNS from ISP automatically
  • set the router to act as DHCP server for the internal network.

Adjusting channels has no effect. Any ideas?

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I've experienced something similar, with the common machine being a laptop younger then that running both vista AND windows 7. Does the laptop have to be actively using the network, or just on to trigger the problems? –  Trezoid Sep 23 '10 at 4:20
    
@Trezoid: I could just be looking for patterns that aren't really there. But yes, when this one laptops uses the internet in any way, the trouble seems to start then for everyone. Regarding age: I also have another ancient, rusty laptop always on running as a server, and it has never appeared to affect DNS queries for anyone else. –  bob-the-destroyer Sep 23 '10 at 4:37
    
The first think I thought of was the laptop could be causing the problem, because it is common to all. Other than a bad driver not playing well on the network, I was concerned that something bad crawled into the laptop and is trying to do an ARP spoof attack on the default gateway (the router). Probably not the problem, but I'm just thinking with my security hat on. However, the reason I thought that is pings not working. Computers cache DNS results and if you ping a place you were just at, then it isn't DNS lookup needed. Also if you ping an IP and the ping dies, it isn't DNS. Good luck –  Scott McClenning Sep 23 '10 at 4:38
    
@Scott McClenning: Browse or ping by IP address always works fine (as far as I can tell). Intranet connections always work fine if by router-assigned IP address. It's just the Internet DNS queries that fail. I'll try and dig up the drivers for this one machine and run through more virus/malware checks to see if that works. –  bob-the-destroyer Sep 23 '10 at 4:40
    
If pinging an IP always works, then it probably isn't something crawling into the machine or a bad driver. One assumption I has I want to confirm is the default gateway assigns IPs with DHCP and resolves DNS (like home routers do). Or is this more corporate where there is a dedicated router, DNS and DHCP each in a box. Also, is there a domain structure? It seems somehow the laptop (or it's IP) could be configured for something on the network and when the laptop doesn't respond there is a timeout. When the laptop is offline, the timeout is less because it knows the laptop is not online. –  Scott McClenning Sep 23 '10 at 5:29

3 Answers 3

What make and model of router - I've seen some (Esp: older Linksys) where their DNS proxying b0rks after a while. Worth seeing if there's a firmware update for the router.

Try fixing one PC to use OpenDNS (208.67.220.220 and 208.67.222.222) or Google (8.8.8.8 and 8.8.4.4) for its resolution and see if this machine keeps going when the others fail.

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Belkin Share N300 802.11n (6 months old), Belkin N Wireless (3 years old), and some unknown older Linksys. I've set one system to use Google DNS, and don't seem to have any issues there. For some reason, if I manually set the DNS IP on the newer Belkin itself to anything else but automatic, it blocks completely. –  bob-the-destroyer Sep 24 '10 at 5:14
    
Try setting the manual DNS on one of the PCs so that it (hopefully) doesn't rely on the router for DNS proxying or for the router to tell it what DNS servers to use and see if that PC behaves when the others don't –  Linker3000 Sep 24 '10 at 8:04
    
doing that now. I'll try it out for a day or so, plus some more synchronized browsing tests to really pinpoint exactly when and why this happens. I've already contacted Belkin a few times, but I think my support case has been thrown in the bin by now. –  bob-the-destroyer Sep 24 '10 at 22:09

You could have a faulty ARP table or being the victim of ARP poisoning. I would flush the ARP table on all the computers on the network and on the Router if you can. Also, ipconfig /flushdns on all the Windows based computers, as this has helped me in some situations.

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Yeah, I've found that ipconfig /flushdns immediately corrects the problem for that system for a few minutes. It almost seems like this intranet is the victim of DNS poisoning by its own routers... –  bob-the-destroyer Oct 15 '10 at 2:35
    
That is entirely possible, I've seen it first hand. Glad you got it resolved. –  brandon927 Oct 15 '10 at 3:53

Self-answered with some help by Belkin tech support, I suppose. After resetting the router to factory defaults, power cycling both the router and the modem, and setting the router to use WEP-64bit for wireless instead of WPA2, all problems seem to have gone away. This is possibly either due to the router carrying over bad configuration (which is not accessible by the user) from being set up on the previous ISP's network, or otherwise due to certain devices on my network not supporting WPA2 encryption and thereby confusing the router.

Also solved by just doing the above was a seemingly unrelated problem where all outside incoming connections on port 80 were always directed to the router main config page rather than forwarded on to a designated virtual server within the network. Port forwarding now works correctly.

The root cause of all this drama is still undetermined, but according to Belkin tech support, a firmware update to address these issues is being developed. Until then, I'm stuck with WEP-64bit.

Edit: I take that back. Above fix only temporarily resolved the DNS issue. Slowly, the problem has been coming back in full force once again.

Edit 2: Wooohoo! After a new firmware update, the problem hasn't yet returned. I'm glad the manufacturer of my current router figured out the issue. If it's a fault with a crappy industry-wide standard, hopefully other manufacturers will follow suit.

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