Question about recursive name resolution

[Mark_Andrews at isc.org]

> Thank you very much for your reply. Now I know the reason why the high level
> name servers do not use recursive name lookup. But if they used this kind of
> method, would the performace be improved because they can use the caching
> data to respond the requests from  clients more quickly? And the network
> traffic would be reduced?

	Marginally which is what some people configure caching
	servers to ask other caching servers first (see forwarders).
	However doing so moves the cost of lookup away from the
	client and to the higher level servers which would then have
	to provisioned to hold the cache and support the extra
	traffic to perform the lookups.  It also make it easier to
	spread bad data.  For these reasons it is not done.

	In other words it doesn't scale and it weakens a already
	weak security model.
 
	Mark

> <Mark_Andrews at isc.org> wrote in message news:apq69u$4p8n$1 at isrv4.isc.org...
> >
> > > Hi,all
> > >
> > > I'm just starting to learn the DNS. One question puzzles me that local
> or
> > > low-level name servers normally use recursive name resolution,but high
> level
> > > name servers closed to the root generally do not support it.Why? And if
> the
> > > high level name servers use recursive name resolution, can we expect
> much
> > > performance improvement? Thank you!
> > >
> > > Jeffery
> >
> > Servers fall into three classes, authoritative, caching and both
> > authoritative and caching.
> >
> > High level servers are generally dedicated to the authoritative
> > role and hence don't need to offer recursion.
> >
> > Low level server are often performing both the authoritative and
> > caching roles hence they offer recursion to some (all) clients.
> >
> > Then there are servers which are only caching servers.
> >
> > Mark
> > --
> > Mark Andrews, Internet Software Consortium
> > 1 Seymour St., Dundas Valley, NSW 2117, Australia
> > PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at isc.org
> >
> 
> 
> 
--
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at isc.org