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I've been having intermittent internet connection issues for a week or so now. I now suspect that these are just DNS issues rather than connection issues.

At the moment I can ping google.co.uk no problem at all (173.194.41.159) but I can't use nslookup to resolve google.co.uk (this is still running from earlier when I limited connectivity using -t. If I try it now name doesn't resolve).

My standard configuration is to use google's public DNS servers but I have tried a few others from this list: http://pcsupport.about.com/od/tipstricks/a/free-public-dns-servers.htm

I always get a

DNS request timed out
    timeout was 2 seconds

my command is:

nslookup google.co.uk 209.244.0.3

On my laptop (currently connected through my phone's 4G) this worked fine.

Web pages for ip addresses work fine and really fast through home broadband. I just can't seem to resolve any IP addresses.

Unfortunately I don't get any support from my ISP at the weekends.

Does anyone have any suggestions?

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On restarting my router I can use nslookup - for about a minute then it stops working again... –  Roaders Jun 14 at 9:54

2 Answers 2

Had the same thing happening to me, able to ping external hostnames but nslookup gave nothing but the '2 second' timeouts.

In my case it turned out to be the firewall software (TinyWall). As soon as I disabled it, nslookup started working.

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Compare the output of traceroute -n -U -p 53 8.8.8.8 to that of traceroute -n -I 8.8.8.8 this will tell you how far your packets to port 53 are getting.

I am guessing your ISP is filtering the internet "for your protection".

One possibility is that they have always been hijacking DNS requests, and though you think you have been trying different DNS providers, your ISP has always been directing every one of your requests to their own DNS server. If that DNS server has crashed, it will appear as if every DNS server is now unreachable.

But there will be a difference in the traceroute output you see depending on whether the ISP is hijacking the requests or not.

Another possibility is that the ISP has been filtering DNS lookups on their own DNS servers, but found customers bypassing this filtering by using other DNS providers. The ISP may now have installed a firewall rule to block very DNS request send to other DNS providers. If that is the case, you'd still be able to resolve hostnames, as long as you use the DNS servers offered through DHCP.

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Do you mean tracert? Those options aren't valid on tracert. (I am on windows 7). Thanks for your reply. I would doubt that my ISP would do anything like that sort of thing. They are Eclipse and they have never blocked, throttled or filtered anything before. It is possible though of course. I wish they had weekend support! –  Roaders Jun 14 at 9:53
    
@Roaders Does name resolution work if you use your ISP's nameservers? Testing that would give a pretty good hint. –  Håkan Lindqvist Jun 14 at 9:56
    
@Roaders I have heard of that Windows thing, but I don't use it myself, and I don't think I know anybody who really understand how it works. I hope you can find somebody else who can tell you how to find a reasonably flexible traceroute tool for Windows. I am using the default one on Ubuntu. –  kasperd Jun 14 at 10:03
    
@HåkanLindqvist I did try that vut couldn't find a listing of my ISPs DNS servers anywhere. –  Roaders Jun 14 at 10:08
    
@Roaders Every ISP I have used handed out that list of DNS servers when you request an IP address through DHCP. And every OS I know of will use that list by default. On Ubuntu you can find the list in /var/lib/dhcp, I have no idea if there is a way to find the list on Windows. –  kasperd Jun 14 at 10:12

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