Subject: Context specific semantics was Re: uncooperative DNSBLs, was several messages
From: Ted Hardie <[email-masked]>
To: Tony Finch <[email-masked]>
Cc: "[email-masked]" <[email-masked]>
Date: Thu, 13 Nov 2008 12:08:17 -0800
List-Id: IETF-Discussion <ietf.ietf.org>

At 11:23 AM -0800 11/13/08, Tony Finch wrote:
>On Thu, 13 Nov 2008, Ted Hardie wrote:
>>
>> Thanks for the pointer. I had missed this technical comment in the
>> crowd, and I think it is very important indeed.  By re-using RRs with
>> context-specific semantics, the proposal does serious harm to
>> interoperability.
>
>Is there any evidence for that?
>
>Tony.
>--
>f.anthony.n.finch  <[email-masked]>  http://dotat.at/
>VIKING NORTH UTSIRE SOUTH UTSIRE: SOUTHERLY OR SOUTHWESTERLY 5 TO 7,
>OCCASIONALLY GALE 8 IN NORTH UTSIRE AT FIRST, AND PERHAPS GALE 8 IN VIKING
>LATER. ROUGH OR VERY ROUGH. RAIN. MODERATE OR GOOD, OCCASIONALLY POOR.

The draft currently says:

   DNSxLs also MAY contain an A record at the apex of the DNSxL zone
   that points to a web server, so that anyone wishing to learn about
   the bad.example.net DNSBL can check http://bad.example.net.

That's an example in which an A record in this zone has the standard DNS meaning
and the expectation is that you can use it construct a URI.  The other A records have
a specific meaning in which the data returned indicates that indicates something about
its reputation in a specific context (what reputation etc. being context specific).  One
of these things is not like the other.  Using the same record type for both  creates
a need to generate some other context that enables you to figure out what was really meant.

The whole approach here is "An A record in this zone has a meaning different from
the meaning in other zones".   That creates a DNS context for the RRTYPE based on
the zone of the query, which is not what the DNS currently uses for disambiguating
the types of requests/responses.  Using a different RR type puts you back into
the standard way of doing things.

			regards,
				Ted Hardie

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