Re: TTL From Parent or Child Zone?

On 1 Jun 2009, at 17:39, Paul Jarc wrote:
> Sabahattin Gucukoglu <[email protected]> wrote:
>> Well yes, but it also makes your cache inaccurate for the case where
>> the delegating name server always holds records that dominate the
>> authoritative data due to long TTLs.
>
> For a given domain name and record type, dnscache keeps the record
> that it received most recently.  So if it's looking up the address of
> www.example.com, and the.com servers say that example.com has the name
> server a.ns.example.com, with the address 1.2.3.4, dnscache will cache
> that - but then once it talks to a.ns.example.com, it will get new
> NS/A records for a.ns.example.com, which will replace the previous
> records in the cache.  So then those records will expire according to
> the TTLs from a.ns.example.com, not the TTLs given by the .com
> servers.

That's fine, but what happens when there's never a need to ask  
authoritative servers?

Suppose I want to look up bigbox.example.net, and that  
bigbox.example.net happens to be in the glue provided by the .net  
nameservers for example.net.  Now the cache gets the answer it wants  
having only gone as far as the .net nameservers.  That data isn't  
authoritative and almost certainly has a very long TTL.  How can  
example.net guarantee that the address record for bigbox.example.net,  
as specified in the example.net zone files and as served by the  
bigbox.example.net nameserver, will be seen by caches?

Cheers,
Sabahattin