Cache strangeness

[Mark_Andrews at isc.org]

> > 	Named supports negative caching (caching of NXDOMAIN and
> > 	NODATA responses).  The length of time this will be cached
> > 	for is controlled by the servers for the reverse zone (see
> > 	RFC 2308).  Named itself will put a upper limit on the ttl
> > 	of negative answers it receives (see max-ncache-ttl, default
> > 	3 hours).
> > 
> > 	Mark
> 
> This is not a function that we wish to support, can this be turned off?

	Do you really know the impact of turning this off?

	The root servers are currently spend the vast majority of
	there time (> 90%) repeatedly answering negative queries
	that could have been avoided if the clients supported
	negative caching.

	Yes, you can tune it but don't turn it off.  You are doing
	a disservice to everyone if you do so.

	Note the DNS has never supported instantaneous changes.
	They take time to propogate to the authoritative servers
	and to expire from the caches.

	Named also has support to see if a name exists without
	resulting in a NXDOMAIN being cached.  If you query for a
	SOA records the resulting NXDOMAIN won't be cached (beyond
	the current clock tick).  'nsupdate' uses this to find the
	enclosing zone when you don't specify the zone to be updated.

	Mark
> 
> 
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Mark Andrews, Internet Software Consortium
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