DNS header format for Query requests

[Cricket Liu]

> I'm trying to diagnose a problem with a piece of equipment that
> seems to be sending badly formed DNS queries. I need to get an accurate
> description of the Header format for a Query request but the maze
> of RFCs is melting my brain.
> 
> Is the Header format in RFC1035 still correct and complete for
> Opcode 0 (Query) requests? I know it's been amended for other Opcodes, 
> Update for instance.
> 
> Specifically tcpdump is seeing Headers with the fourth byte set to
> 0x40: which mean the first ``Z'' bit is set. Have any of the Z bits
> been defined for Query requests?

Two of the Z bits are defined as the AD and CD bits in
RFC 2535.

cricket

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