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How can I check through my browser whether my DNS is working or not? The context is that my ISP's DNS servers sometimes go down for a few minutes. So sometimes net connectivity problems are due to DNS errors. I can go to the command line and do nslookup, but it's cumbersome. So what are easy ways to check whether DNS is working through the browser? I am using firefox-4.

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If the DNS servers from your ISP gives you trouble why not using an other DNS server? I think the DSN server from Google is located at 8.8.8.8 or 8.8.4.4. – JordyOnrust Jun 7 '11 at 10:20
@Bright010957:I remember reading somewhere that using public DNS can lead to some speed problems when using CDN services(like youtube etc.), because in their case they use DNS to redirect to a server near your location. – apoorv020 Jun 7 '11 at 10:24
Why not change the DNS servers you are using? Pick a more reliable DNS server. – Moab Jun 7 '11 at 10:36
@Bright:Found the relevant slashdot article apple.slashdot.org/story/10/12/31/0110226/… – apoorv020 Jun 7 '11 at 13:25
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5 Answers

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A quick check may be to try and pop over to http://www.downforeveryoneorjustme.com/ and do a lookup - which may or may not work (the site will tell you) according to external factors. If you cannot even get to the site then it's probably your ISP's DNS playing up.

You might consider not using your ISP's DNS servers at all (unless they specifically forbid or block this option) and change your DNS settings to use a free third party service such as:

Google: 8.8.8.8 and 8.8.4.4

OpenDNS: 208.67.220.220 and 208.67.222.222

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If I cannot get to the site, then I may actually be facing internet connectivity problems, so that doesn't help. – apoorv020 Jun 7 '11 at 10:25
Well, if you have connectivity problems then you are going to have to try something to find the root cause - you have to start somewhere. – Linker3000 Jun 7 '11 at 11:57
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I don't know why you say through a browser. You simply can't tell from a browser if it is a connectivity problem, or DNS, since if DNS is broken, the browser will tell you nothing about connectivity since it just won't connect.

  1. Check Internet connectivity by opening a command box and ping 8.8.8.8
  2. If you don't trust your local ISP's DNS, change to Google's 8.8.8.8 and 8.8.4.4. Based on your comment, if you do experience problems with DNS somehow telling youtube to send you to a specific server, which is distant to you, search other local ISP's, and find their settings for DNS, and use them. I have my doubts that that is a real issue, although any change in route from your PC to a site potentially can have a misconfiguration in it.
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Try to input an ip address of some host in the address bar and press enter. Then try to input the domain name of that ip address, if this time it fails then DNS is malfunctioning.

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Yeah, I wondered about this. Are there any domains whose ip doesn't change? – apoorv020 Jun 7 '11 at 10:20
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Most of them. You could try: 64.34.119.12 . This is the ip of stackoverflow. – Jarco Jun 7 '11 at 12:32
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Using the wrong tool for the job, however much less "cumbersome" it may be, is still using the wrong tool for the job. A WWW browser is not a DNS diagnosis tool. However hard it may be to use a tool where you have to type something simple like dig a www.example.net. into the computer, that is nonetheless what you have to do. Abusing the wrong tool to do the job will at best have you chasing all sorts of wild geese, from plug-ins to proxy auto-configuration. Use the right tool for the job. Use a DNS diagnosis tool to diagnose DNS problems.

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I'm not looking to use the browser as a DNS diagnostic tool. Merely whether DNS is the error point. Plus, the browser should have tools to check internet connectivity, since it's almost the sole gateway to the internet for most people. – apoorv020 Jun 7 '11 at 16:55
If you are checking whether DNS is the fault locus then diagnosing DNS problems is exactly what you are doing and using the correct tools for that job, and not a WWW browser, is exactly what you should be doing. Even a modicum of thought would reveal what tripe your final sentence is; by its argument WWW browsers should contain every single task that anyone would ever want to do. Stop wanting to abuse the wrong tool and complaining that the wrong tool should do the job that you want instead of its own job, and use the right tool for the job. – JdeBP Jun 8 '11 at 8:53
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Not directly an answer to your question but maybe to your problem. If you connect to the Internet using a router, try enabling its DNS feature and using it as your PC's DNS server. Now on the router, have it default to your ISP's DNS server, but have a second (third) option of 8.8.8.8 and/or 8.8.4.4. That way, if the ISP's server doesn't answer, the router will try the backup DNS.

Not all consumer routers will allow this, but if yours does it will work around the problem.

You could also make 8.8.4.4 or whatever your PC's secondary DNS, used only if the primary is not available. Under *nix-type OSes this requires a very simple step: add one line to the /etc/resolve.conf file. I don't off the top of my head know how to do it under Windows.

Actually the elegant solution is to call your ISP's help line every time their DNS goes down, until they fix the problem.

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