Which DNS servers are used?

[John Gray]

Having come across a situation where unexplained internet access 'hangs' occasionally occurred, I found that the user's router had been configured with a primary DNS server IP address which was valid and a secondary DNS server IP address which was (now) entirely dead. I got to thinking: how could one find out which DNS server responds to a DNS query? It seems that 'some software' will rotate the order of the specified DNS servers tried and 'other software' will always go to the preferred DNS server, then to any others if the preferred server does not respond (and sometimes just gives up after the first!).

Has anyone come across any software which could monitor the use of the router's specified DNS server addresses?

PS I found that one of Steve Gibson's pieces of free software, DNSbench, was very useful for DNS server testing. I also found it interesting how (comparatively) slow were the Open DNS and Google DNS servers in the UK as opposed to "Level 3 Communications" (who? Verizon?)...

[StuartR]

The best way to do this would be to install dig on your Windows PC and then the command
dig +trace http://www.eileenslounge.com" onclick="window.open(this.href);return false;
(or any other DNS name that you want to look up) will show all of the DNS servers involved in the chain that answered the query.

dig is not very easy to install on Windows, you can use your favourite search engine to look for "dig for windows" and that will take you to sites where you can download the files and provide instructions for how and where to unpack them.

You could try using dnstracer, I have never used this software but it looks like it should do what you want

dnstracer is a software that determines where a given Domain Name Server (DNS) gets its information from, and follows the chain of DNS servers back to the servers which know the data.

[John Gray]

Thank you! I'll look through these two...