Re: [DNSOP] "Optimization" in draft-ietf-dnsop-qname-minimisation

[Tony Finch <[e-mail]>]

Jelte Jansen <[e-mail]> wrote:
> On 01/05/2015 05:55 PM, Bob Harold wrote:
> >
> > I would expect "www.something..." to be in the same zone as
> > "something..." in most cases, so I think it is actually very common to
> > have more than one level on the same DNS.
>
> Would you? I'd expect 'www' there to be in 'something', and 'something'
> to be in a TLD (assuming context of a 3-label domain, not counting root)
>
> So for www to be in the same as something would mean it'd be in the TLD...

I think Bob means that www.something is not a zone cut. If it is a zone
cut then the authoritative RRs for www.something can be on different name
servers to something, e.g.

.		NS	a.root-servers.net
at.		NS	d.ns.at.
dotat.at.	NS	black.dotat.at.
www.dotat.at.	NS	lb.dotat.at
www.dotat.at.	SOA	lb.dotat.at. (...)
www.dotat.at.	AAAA	2001:...

So if you use an NS query to probe zone cuts, a straightforward
implementation of query minimization requires four queries for a three
label name (if the resolver has a primed but empty cache).

If you use A queries you save a lookup in the common case where there
isn't a zone cut at the leaf.

Tony.
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