Cache Entries

[Kevin Darcy]

Robert Spangler wrote:
> Hello,
>
> A question has been raised about TTL and cached entries.  After the first 
> request do the following request reset the cache TTL or does the entry 
> continue to count down until it expires and once it reaches zero the cache is 
> is cleared until the next request which starts the process all over again?
>   
Once an answer is cached, you answer from the cache until the TTL 
expires, at which point you go and fetch a fresh set of records. The 
only way I could see the TTL being "reset" is if the same data was seen 
in a response to some other query (e.g. part of a CNAME chain) that is 
of equal or higher credibility/trustworthiness/rank (a la RFC 2181). 
Then maybe the new data would "refresh" the old cache TTLs. But I 
haven't actually tested this in practice. Modern BINDs have a lot of 
protection against cache poisoning, so it's possible that such 
"refreshes" will no longer occur.

- Kevin