Case-Insensitive Response Compression May Cause Problems With Mixed-Case Data and Non-Conforming Clients

Tony Finch dot at
Mon Feb 10 15:52:15 UTC 2014

Paul Vixie <paul at> wrote:
> i regret not saving your original example. can you show me a case where
> the first time a label is seen, it's not from an authority?

The example was a question for _kerberos._udp.UXSUP.CSI.CAM.AC.UK in which
_udp UXSUP CSI are empty non-terminals and is the SOA. If you
ask for an A record instead of a SRV (as I did by accident) you get a
negative answer. The answer from the authority server does not include the
canonical versions of the intermediate labels, so the negative cache entry
is created using the labels from the question.

If you later create positive cache entries under these labels (by asking
for SRV) you get the first answer back with canonical case (because it is
copied from the authoritative answer) but subsequent answers from the
cache use the same case as the negative cache entry.

f.anthony.n.finch  <dot at>
Forties, Cromarty: East, veering southeast, 4 or 5, occasionally 6 at first.
Rough, becoming slight or moderate. Showers, rain at first. Moderate or good,
occasionally poor at first.

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