recursive/iterative/explicit queries...
Joseph S D Yao
jsdy at center.osis.gov
Thu Nov 1 19:17:16 UTC 2001
On Thu, Nov 01, 2001 at 01:55:07PM -0500, Popescu, Adrian wrote:
> According to your response, there is a parameter in the res_query/res_nquery
> resolver functions, that is used to define a query as recursive/iterative:
I'm afraid that I said no such thing.
Please cf the following, also found in Appendix A of D&B 3E. These are
the bits of the actual query sent out on the wire.
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RFC 1035 Domain Implementation and Specification November 1987
...
4. MESSAGES
4.1. Format
All communications inside of the domain protocol are carried in a single
format called a message. The top level format of message is divided
into 5 sections (some of which are empty in certain cases) shown below:
+---------------------+
| Header |
+---------------------+
| Question | the question for the name server
+---------------------+
| Answer | RRs answering the question
+---------------------+
| Authority | RRs pointing toward an authority
+---------------------+
| Additional | RRs holding additional information
+---------------------+
The header section is always present. The header includes fields that
specify which of the remaining sections are present, and also specify
whether the message is a query or a response, a standard query or some
other opcode, etc.
...
Mockapetris [Page 25]
RFC 1035 Domain Implementation and Specification November 1987
4.1.1. Header section format
The header contains the following fields:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode |AA|TC|RD|RA| Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ANCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NSCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
...
Mockapetris [Page 26]
RFC 1035 Domain Implementation and Specification November 1987
...
RD Recursion Desired - this bit may be set in a query and
is copied into the response. If RD is set, it directs
the name server to pursue the query recursively.
Recursive query support is optional.
RA Recursion Available - this be is set or cleared in a
response, and denotes whether recursive query support is
available in the name server.
...
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--
Joe Yao jsdy at center.osis.gov - Joseph S. D. Yao
OSIS Center Systems Support EMT-B
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