[afnog] Iterative Request

[Stephane Bortzmeyer]

Stealing threads is really bad
<http://wiki.exim.org/MailingListEtiquette#Thread_Stealing>

On Fri, Oct 12, 2012 at 08:23:08AM +0100,
 Anibe Onuche <a.onuche at nixp.net> wrote 
 a message of 19 lines which said:

>  For example.
>  
>  AAA.BBB.CCC.DDD.com
>  
>  Does the Caching server caches the IP address of .com, DDD.com, 
>  CCC.DDD.Com, BBB.CCC.DDD.Com and AAA.BBB.CCC.DDD.com or it simply 
>  caches the AAA.BBB.CCC.DDD.com?

.com, like most TLDs, have no address record so there is no such thing
as "the IP address of .com". But, yes, NS records for .com will be
cached (otherwise the DNS would melt rapidly), as well as the
intermediary domains (if there is a zone cut, which is not mandatory,
for instance BBB.CCC.DDD.Com may be a subdomain of CCC.DDD.Com but not
a sub-zone).

You can see this yourself easily with tcpdump: start with a cold
resolver, if you request AAA.BBB.CCC.DDD.com, then example.com, your
resolver will not send requests to the root name servers the second
time.