Diagnosing "NO DNS" messages

DNSThe Domain Name System is a world-wide directory that allows the identification of a networked computer using words - the Domain Name - instead of numbers - the I.P address. See Wikipedia's article on DNS for more information stands for Domain Name System and it is the method used on the Internet to convert between human-friendly names such as www.guralp.com to the IP addresses which are used by the underlying network. Each PC needs to know the address of a DNS server, to which it passes queries when it needs to contact another system over the Internet.

For most people, their DNS server is specified for them - either by their Internet Service Provider (ISP) or by their IT department. If you use ADSL broadband, for example, your ISP will provide, specify and maintain a DNS server for you without you needing even to be aware of it. For universities and larger organisations, the IT department will normally maintain an on-site DNS server to reduce the traffic on their Internet link (by cacheing results) and to provide a service for local host-names.

The error means that your DNS server is broken, incorrectly specified or incorrectly configured. It may be possible to fix the problem by clicking the "Fix connection problems" button shown in your screen-shot. If you can contact other sites but not www.guralp.com, this probably means that your DNS server is broken.

To identify and test your DNS server, open a command window and type

nslookup www.guralp.com

(This works on both Windows and Linux.) The output will look like this:

Server: 198.51.100.20 Address 1: 198.51.100.20 obfusc.guralp.local Name: www.guralp.com Address 1: 46.43.14.141 torunska.default.ppiorunski.uk0.bigv.io Address 2: 2001:41c9:1:423::141 torunska.default.ppiorunski.uk0.bigv.io

The first lines tell you which DNS server you are currently using. In the example above, it is obfusc.guralp.local at address 198.51.100.20. The subsequent lines show you the name being looked up, the IP address(es) associated with that name and the canonical names of the hosts at those addresses.

If the DNS server that this identifies is provide by your ISP, you should complain to them; similarly, if it is provided by your IT team, you should raise the issue with them.

You can also test the same name against different DNS servers. For exampe, openDNS provide a free, public DNS server at 208.67.222.222. To test what this server says, type

nslookup www.guralp.com 208.67.222.222

Expect output like

Server: 208.67.222.222 Address 1: 208.67.222.222 resolver1.opendns.com Name: www.guralp.com Address 1: 46.43.14.141 torunska.default.ppiorunski.uk0.bigv.io

The results are the same as in the previous case but you can see that we have queried a different server.

There are a number of free, public DNS servers that you can use instead: These include 1.1.1.1, 8.8.8.8, 9.9.9.9 and 64.6.64.6. I can't give you instructions for configuring your PC to use these because I do not know what operating system you are running.