Re: [DNSOP] WGLC: "Considerations for the use of DNS Reverse Mapping"

> On Tue, Apr 01, 2008 at 06:34:38AM +1100, Mark Andrews wrote:
> > 
> > 	Multiple PTR records do not scale.
> 
> 	what does that mean Mark?
> 	
> 	why does "Multiple A records" scale and not others?
> 	is this a DNS protocol issue or an implementation artifact?

	Multiple PTR records scale worse than multiple A records.

	You get ~4000 A records in 64K.
	You get ~2000 AAAA records in 64K.

> > 	Today we have reverse lookups that fail because people
> > 	followed this path and exceeded the 64K DNS message size
> > 	of TCP.
> 
> 	and the same failure would be true for multiple instances
> 	of any RR type. 

	Yes.  It's just very very rare for there to be enough of
	the other types to cause a problem.

	It's not uncommon for there to be too many PTR records to
	cause a problem especially when you start advocating that
	each address records needs a corresponding PTR record.  The
	only reason we don't see more problems is that people have
	been saying that it is a waste of time to have multiple PTR
	records.

> > 	When people have a 100 thousand virtual domains on a 
> > 	box you just can't have PTR records for all of them.
> 
> 	and apparently you can't have A records for them either.
> 
> > 
> > 	Mark
> 
> 	so the actual spec limit is any mixture of RR types that
> 	will fit into a 64k DNS message on TCP.  Right?
> 
> --bill
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews@isc.org
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