header
Click on the red underlined text to get to the source
... off nodes. The remaining
RR parts are the fixed header (type, class, TTL) which is consistent for
...
... and responses are carried in a standard message format. The
message format has a header containing a number of fixed fields which
are always present, and four sections which carry query parameters and
...
...
The most important field in the header is a four bit field called an
opcode which separates different queries ...
...
Note that the content, but not the format, of these sections varies with
header opcode.
...
... queries do not have recursion desired (RD)
in the header. Note that the answers to non-recursive queries do depend
on the server being asked, but do not depend on the identity ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY |
+---------------------------------------------------+
Question | QNAME=SRI-NIC ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY,RESPONSE |
+---------------------------------------------------+
Question | QNAME=SRI-NIC ...
...
This response is different from the previous one in two ways: the header
does not have AA set, and the TTLs ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE |
+---------------------------------------------------+
Question | QNAME=SRI-NIC ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE |
+---------------------------------------------------+
Question | QNAME=SRI-NIC ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
... AA and
RESPONSE bits in the header. The interpretation of this response is
that the server is authoritative for the name, and the name exists, but
no RRs ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA, RCODE=NE ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE |
+---------------------------------------------------+
Question | QNAME=BRL.MIL, QCLASS=IN ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
... Note that the AA bit in the header guarantees that the data matching
QNAME is authoritative, but does not say anything about whether the data
for C.ISI.EDU is authoritative. This complete reply is possible because
...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY |
+---------------------------------------------------+
Question | QNAME=ISI.EDU., QCLASS=IN ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE |
+---------------------------------------------------+
Question | QNAME=ISI.EDU., QCLASS=IN ...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...
...
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA |
+---------------------------------------------------+
...