[bind10-dev] question about configure option "zero-no-soa-ttl" in bind9

[Mark Andrews]

In message <498616095.01087 at cnnic.cn> <006701cbd4b7$0d67ef10$2837cd30$@cn>, "zh
anglikun" writes:
> Hi Mark,
> 
> I noticed there is one configure option " zero-no-soa-ttl " in bind9.  =
> The comments for it in bind9's code is: "If the query was for a SOA =
> record force the ttl to zero so that it is possible for clients to find =
> the containing zone of an arbitrary name with a stub resolver and not =
> have it cached."
> 
> My question is: what it will change if the negative response for soa =
> query is cached?
> 
> My guess it will benefit to the query for the frequent deleted/added =
> zones. Some zones may be added or deleted frequently, if the negative =
> response for soa query is cached, the resolver only can get the newest =
> zone information until the negative reponse expires. Am I right?
> 
> Thanks
> Likun

The option is to allow one to find the containing zone of a name to be
added to the dns without it causing side effects.

	dig soa <name.to.be.added> -> nxdomain
	dig soa <to.be.added>	   -> nxdomain
	dig soa <be.added> 	   -> soa
	dig soa <added> 	      not done
	dig soa .	              not done

	nsupdate 
	zone be.added
	update add name.to.be.added 3600 A 1.2.3.4
	send

Without this the cache may contain a nxdomain response which prevents the
newly added records being returned.

https://tools.ietf.org/tools/rfcmarkup/rfcmarkup.cgi/draft-andrews-dnsext-soa-discovery-00

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org