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Re: provisioning software, was DNS RRTYPEs, the difficulty with

2012-03-08 20:08:51
Sorry,

s/some 3-4 conditions/some 3-4 dozen conditions/

Martin Rex wrote:

Martin Rex wrote:

So if the behaviour (how to exactly respond to queries for unknown
QTYPEs) is neither explicitly specified, nor likely have been part of
the usual/common interop tests performed by the vendor,
what you're left with might be "ureflected&untested guessing"
on part of the implementors to fill those gaps.

What you typically have is a certain amount of code processing a query,
and some 3-4 conditions under which this code fails, and where the
implementor will have to decide which RCODE to return.  The choices
available in rfc1035 are:

RCODE           Response code - this 4 bit field is set as part of
                responses.  The values have the following
                interpretation:

                0               No error condition

                1               Format error - The name server was
                                unable to interpret the query.

                2               Server failure - The name server was
                                unable to process this query due to a
                                problem with the name server.

                3               Name Error - Meaningful only for
                                responses from an authoritative name
                                server, this code signifies that the
                                domain name referenced in the query does
                                not exist.

                4               Not Implemented - The name server does
                                not support the requested kind of query.

                5               Refused - The name server refuses to
                                perform the specified operation for
                                policy reasons.  For example, a name
                                server may not wish to provide the
                                information to the particular requester,
                                or a name server may not wish to perform
                                a particular operation (e.g., zone
                                transfer) for particular data.

                6-15            Reserved for future use.


The choice between RCODEs 1, 2 and 4 for failed AAAA queries
might be fairly random, the description for 3 is slightly confusing
in whether a DNS server might use this RCODE "creatively" by
returning it without AA.

For an implementor that is being told "do not use use RCODE 4 for
unknown QTYPES", not sending any response at all to an unsupported
AAAA query seems like a reasonable choice.


-Martin


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