BIND started replying to queries for .com with .COM

Mark Andrews marka at
Wed Mar 30 11:25:15 UTC 2016

In message <56FBB385.5070203 at>, Phil Mayers writes:
> On 30/03/16 01:19, Mark Andrews wrote:
> >
> > Your monitoring probe is broken.
> >
> > STD 13 says that that the DNS is case preserving.  The problem is
> > that lots of servers aren't case preserving instead they echo back
> > the query case in the owner names of records returned which named
> > then records.
> Can I be clear on what you think would be the correct behaviour here?
> Presumably the question section should exactly match what the client 
> sent always, bit-for-bit, so we're talking about the ans/auth/add 
> sections - they should, in your reading of the standards, match the case 
> of the on-disk authoritative data, not what the client sent, yes?

> Am I correct in assuming that, by case-sensitively compressing labels 
> for many years, bind has been doing the opposite (the label compression 
> effectively throwing away the carefully case-preserved data)?

It was doing case insensitive compression.  It now does case sensitive
compression.  The rdata was fixed long ago when we went from 1
record per message in a zone transfer to many records as that
resulted in rdata having different case than what was entered.
AXFR/IXFR have been using case sensitive compression for over a
decade now.

The recent change was to record and return the learnt case of
ownernames (to the RRset level) rather than use whatever was used
to build the red-black tree names.


> I'm curious why this has come to the fore now, if you're able to say?
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at

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