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

Chris Thompson cet1 at cam.ac.uk
Thu Feb 6 13:16:53 UTC 2014


On Feb 3 2014, Michael McNally wrote:
[...]
>The remainder of this posting explains the potential issue,
>which we believe will not affect most operators, but you
>should be aware of the potential in case you are one of
>those affected.  This explanation is also provided in our
>Knowledge Base:  https://kb.isc.org/article/AA-01113

I can't help feeling that the title of that article ought to be
"Case-Sensitive Response Compression May Cause Problems With
Mixed-Case Data and Non-Conforming Clients" (rather than
"Case-Insensitive ..."), as that is what BIND 9.9.5 etc. do.

There an aspect of this change which may delay the reporting of
any problems that it causes. As long as nearly all authoritative
nameservers use the old (case-insensitive) compression rules,
recursive nameservers will receive and cache RRs with whatever
name casing they were first queried with. So even when they use
the new (case-sensitive) compression rules themselves, they will
only respond to clients with different casing in the question
and answer sections if they have themselves been queried for
the same name with different casings (possibly by different
clients, of course).

-- 
Chris Thompson
Email: cet1 at cam.ac.uk


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