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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Other values are reserved for future use:<br />

AA Authoritative answer flag. If set in a response, this flag<br />

specifies that the responding name server is an authority for<br />

the domain name sent in the query.<br />

TC Truncation flag. Set if message was longer than permitted on<br />

the physical channel.<br />

RD Recursion desired flag. This bit signals to the name server that<br />

recursive resolution is asked for. The bit is copied to the<br />

response.<br />

RA Recursion available flag. Indicates whether the name server<br />

supports recursive resolution.<br />

Zero 3 bits reserved for future use. Must be zero.<br />

Rcode 4-bit response code. Possible values are:<br />

0 No error.<br />

1 Format error. The server was unable to interpret the<br />

message.<br />

2 Server failure. The message was not processed because<br />

of a problem with the server.<br />

3 Name error. The domain name in the query does not exist.<br />

This is only valid if the AA bit is set in the response.<br />

4 Not implemented. The requested type of query is not<br />

implemented by name server.<br />

5 Refused. The server refuses to respond for policy reasons.<br />

Other values are reserved for future use.<br />

QDcount An unsigned 16-bit integer specifying the number of entries in the<br />

question section.<br />

ANcount An unsigned 16-bit integer specifying the number of RRs in the<br />

answer section.<br />

NScount An unsigned 16-bit integer specifying the number of name server<br />

RRs in the authority section.<br />

ARcount An unsigned 16-bit integer specifying the number of RRs in the<br />

additional records section.<br />

Chapter 12. Directory <strong>and</strong> naming protocols 441

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