SOA TTL in negative answers

[Mark Andrews]

	See draft-andrews-soa-discovery-02.txt and zero-no-soa-ttl

In message <alpine.LSU.2.00.1206061829510.10076 at hermes-2.csi.cam.ac.uk>, Tony Finch writes:
> Not sure if this is a BIND question or a standards question.
> 
> I'm experimenting with some stats gathering. To get the zone of a domain
> name I'm making a SOA query, which will either return a positive answer
> (if the domain is a zone apex) or a negative answer with the enclosing
> zone's SOA in the authority section.
> 
> I noticed that the TTL on the SOA in NXDOMAIN replies is always zero.
> If I query for a different nonexistent type then the TTL is what I expect.
> This weirdness doesn't occur for noerror/nodata.
> 
> $ dig +noall +authority soa nxdomain.dotat.at
> dotat.at. 0 IN SOA black.dotat.at. dot.dotat.at. 757 3600 600 604800 60
> 
> $ dig +noall +authority txt nxdomain.dotat.at
> dotat.at. 60 IN SOA black.dotat.at. dot.dotat.at. 757 3600 600 604800 60
> 
> $ dig +noall +authority soa www.dotat.at
> dotat.at. 60 IN SOA black.dotat.at. dot.dotat.at. 757 3600 600 604800 60
> 
> $ dig +noall +authority txt www.dotat.at
> dotat.at. 60 IN SOA black.dotat.at. dot.dotat.at. 757 3600 600 604800 60
> 
> I note that BIND and NSD behave differently:
> 
> $ dig +noall +authority soa nxdomain. @f.root-servers.net.
> . 0 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2012060600 1800 900 604800 86400
> 
> $ dig +noall +authority soa nxdomain. @l.root-servers.net.
> . 86400 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2012060600 1800 900 604800 86400
> 
> Tony.
> -- 
> f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
> Lundy, Fastnet: Mainly south becoming cyclonic, 4 or 5 increasing 6 to gale 8,
> occasionally severe gale 9 later. Moderate becoming rough or very rough,
> occasionally high later in south. Rain. Moderate, occasionally poor.
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org