[dns-operations] specifics of UDP response with truncate bit; odd google fail on AAAA responses w/ truncation

[Roy Rapoport]

On 5/24/12 10:20 PM, David Miller wrote:
>>> - Should a packet with the truncate bit set have the field for the number of Answers reflect how many answers are in that packet, or how many are in the actual forthcoming response?  I believe that it should contain the number of RRs contained in the UDP response itself, not the full answer to the query - and this is where I believe the Amazon response is malformed.  In the UDP response it says there are 24 answer RRs when there are zero
>> the header counts must match the actual contents but the
>> prospective/desired contents, or else the response is malformed.
> There was supposed to be a "not" somewhere in this sentence?

RFC 1035 (http://www.ietf.org/rfc/rfc1035.txt) states, on page 27, 4.1.1:

"ANCOUNT         an unsigned 16 bit integer specifying the number of
                 resource records in the answer section."

So I think what Paul may have meant is "the header counts must match the 
actual content, NOT the prospective/desired contents, or else the 
response is malformed"

-roy