RFC 2929 (rfc2929) - Page 2 of 12
Domain Name System (DNS) IANA Considerations
Alternative Format: Original Text Document
RFC 2929 DNS IANA Considerations September 2000
1. Introduction
The Domain Name System (DNS) provides replicated distributed secure
hierarchical databases which hierarchically store "resource records"
(RRs) under domain names.
This data is structured into CLASSes and zones which can be
independently maintained. See [RFC 1034, 1035, 2136, 2181, 2535]
familiarity with which is assumed.
This document covers, either directly or by reference, general IANA
parameter assignment considerations applying across DNS query and
response headers and all RRs. There may be additional IANA
considerations that apply to only a particular RR type or
query/response opcode. See the specific RFC defining that RR type or
query/response opcode for such considerations if they have been
defined.
IANA currently maintains a web page of DNS parameters. See
.
"IETF Standards Action", "IETF Consensus", "Specification Required",
and "Private Use" are as defined in [RFC 2434].
2. DNS Query/Response Headers
The header for DNS queries and responses contains field/bits in the
following diagram taken from [RFC 2136, 2535]:
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|AD|CD| RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT/ZOCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ANCOUNT/PRCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NSCOUNT/UPCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The ID field identifies the query and is echoed in the response so
they can be matched.
Eastlake, et al. Best Current Practice