Slow DNS resolution - just one particular domain

Question

Regarding my last question. I know now, that problem lies in slow DNS resolution. What can cause that, if user says that he has problems only with that one particular domain.

Slow resolution:

• example.com
• foo.example.com
• allsubdomains.example.com

Weird thing is that user has no problem with another domain on same DNS server, redirecting to same IP as example.com.

And btw. shouldn't be domain somehow cached on user end? Because he has all the time problem with slow loading. I told him do flush DNS cache in Windows, but that doesn't helped.

Unfortunately I can't debug DNS server, because we are using our domain registrar DNS servers.

Answer 1

Get him to run nslookup, and turn debug on,

nslookup
>set debug
foo.example.com

And then post the output. If you like, get him to do the same thing with a working domain and post the output for that too. Remember, he won't be talking directly to the DNS servers your registrar uses, he'll be talking to his own DNS servers (or his ISP / Company DNS servers) and reliant on them.

To be frank, if he's the only person with this issue, and you can't replicate it directly on your DNS servers and the DNS entries are right - it's his problem to fix. But, with output from nslookup you might be able to assist.

Answer 2

For the problematic domain, have/can you test with its IP address directly? If it is truly DNS related, then the IP access should not exhibit the slowness challenges. Does it?