Remote site time left in cache?

[Ketil Froyn]

Tuc at T-B-O-H wrote:
> 	A friend of mine does frequent updates to her domain name . She
> wants to know if there is a way to find out given any remote DNS server
> how long it still has in the cache before its checked.

Hi,

I'm not sure what your friend is trying to achieve, but the question 
does not account for programs looking up a name and then remembering the 
result. For instance, some browsers cache names for 30 minutes, so if a 
person writes a name into the browser, the authoritative cache might not 
be queried even though the dns cache has expired the entry 29 minutes ago.

But an answer to the question might be to check the logs of the 
authoritative dns server and see what time the remote server in question 
last queried it. You'll need some logic, because sometimes a server 
includes answers you didn't specifically ask for (like additional 
records). Knowing that, and the ttl of the records in question, you 
could work it out.

For remote servers that aren't in the logs, they will probably be 
forwarding dns servers, and then you're in trouble. You could try 
querying it, but it probably won't answer.

In short, there's no sure way to get the answer you are looking for in 
all cases.

Best Regards,
Ketil Froyn
ketil at froyn.name
http://ketil.froyn.name/