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Sometimes when I try to go to a website on a Win 7 SP1 system, I get a "Server Not Found" error in Firefox and a "This page can't be displayed" error in Internet Explorer.

When I test the site via a tool such as Downforeveryoneorjustme, the site is reportedly working just fine.

So I attempt to figure out what is going wrong. My next step is to flush the DNS cache with ipconfig / flushdns. Then I try a tracert. In these situations, the response from tracert is always "Unable to resolve target system name [URL]".

I will then try nslookup. nslookup gives a "DNS request time out" error, but only for URLs that are experiencing this issue. All other nslookup requests work as expected. Why would this happen?

What other steps can be used to troubleshoot this situation?

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    You probably have a DNS problem. Try using a public DNS server like Google's (8.8.8.8 and 8.8.4.4).
    – Ron Maupin
    Dec 6, 2015 at 7:19
  • @RonMaupin Thanks. I updated the question with more details.
    – End Anti-Semitic Hate
    Dec 6, 2015 at 7:28
  • Try a good DNS server, like Google. If you are using the DNS from your ISP, it could be having problems (nslookup uses your DNS server).
    – Ron Maupin
    Dec 6, 2015 at 7:31
  • The problem you describe is surely a problem with DNS servers. The suggestion to substitute Google's DNS servers for whatever you have now is an excellent suggestion, but it may not be enough if what you are experiencing is DNS censorship, applied by your ISP. Some ISPs do it. There is one simple way around it, if this is your problem drop me a comment, I will show you how to circumvent this despicable behavior.
    – MariusMatutiae
    Dec 6, 2015 at 8:13

1 Answer 1

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Your problem sounds like one of censorship. This is often done on DNS requests, by ISPs an/or governments, because it reduces the burden on the censoring apparel greatly: blocking the loading of, say, a forbidden newspaper Web page would entail identifying and analyzing thousands of packets, while blocking DNS simply implies re-routing a single packet (or maybe a handful, if the original query receives no answer). This makes censoring a whole network feasible.

There is one instrument which will allow to diagnose that, Google's Namabench. There is a version available for every OS, just make sure you tick, on the opening mask, the box Include censorship checks.

If you want to get around a problem of censorship, then you should use DNSCrypt, a lightweight piece of software, again available for all OSes (for those using Linux, not you, it is in the repos), which

  1. encrypts DNS requests;

  2. moves requests to a port other than 53.

This is done to evade DNS-blocking software which can identify DNS requests on the basis of port and/or protocol. The service being queried by default is OpenDNS, a highly reputable service.

It should be a fire and forget installation.

If this does not solve your problem, then it means you are behind a nasty firewall which does provide individual-packet inspection, besides DNS-hijacking. But we'll blow that bridge when we get there.

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  • Its not necessarily censorship. My ISP used to have a fairly innocent webcomic about inept alien invaders who loved cake occationally null routed. I used to ssh tunnel just to read that. It might be simple ineptitude ;p
    – Journeyman Geek ♦
    Dec 6, 2015 at 11:05
  • @JourneymanGeek Agreed. But the above ought to take care of some ineptitudes too.
    – MariusMatutiae
    Dec 6, 2015 at 11:31

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