RD
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... Queries contain a bit called recursion desired or RD. This
bit specifies specifies whether the requester wants recursive
...
...
The recursive mode occurs when a query with RD set arrives at a server
which is willing to provide recursive service; the client ...
... client can verify
that recursive mode was used by checking that both RA and RD are set in
the reply. Note that the name server should never perform recursive
...
... the reply. Note that the name server should never perform recursive
service unless asked via RD, since this interferes with trouble shooting
of name servers and their databases.
...
... service. If recursive service is available and
requested via the RD bit in the query, go to step 5,
...
... name server behavior.
Unless otherwise noted, the queries do not have recursion desired (RD)
in the header. Note that the answers to non-recursive queries ...