[dns-operations] Name server turning off RD bit in response - just curious

[Faasen, Craig]

Hello,

I noticed that the "rd" flag was missing from the output of a standard (recursive) dig against some (*) of the name-services.com name servers:
$ dig @dns5.name-services.com. name-services.com. | grep flags
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 5, ADDITIONAL: 5

(*) dns1 and dns5 show this behavior, dns2-4 are "normal".

Using dig.pl (Net::DNS::Toolkit):
$ dig.pl -h @dns5.name-services.com. name-services.com.

  ID      => 4439
  QR      => 0
  OPCODE  => QUERY
  AA      => 0
  TC      => 0
  RD      => 1
  RA      => 0
  Z       => 0
  AD      => 0
  CD      => 0
  RCODE   => NOERROR
  QDCOUNT => 1
  ANCOUNT => 0
  NSCOUNT => 0
  ARCOUNT => 0

  ID      => 4439
  QR      => 1
  OPCODE  => QUERY
  AA      => 1
  TC      => 0
  RD      => 0
  RA      => 0
  Z       => 0
  AD      => 0
  CD      => 0
  RCODE   => NOERROR
  QDCOUNT => 1
  ANCOUNT => 1
  NSCOUNT => 5
  ARCOUNT => 5

; <<>> dig.pl 1.11 <<>> -h @dns5.name-services.com. name-services.com.
;;
;; Got answer.
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4439
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 5, ADDITIONAL: 5

<snip>
 
RD is set to 1 in the query, but is 0 in the response.
Which is not compliant with RFC 1035: "RD Recursion Desired - this bit may be set in a query and is copied into the response."

Out of curiosity, any idea why a name server would want to change the RD bit ? (except to break an unsuspecting script ;)

Thanks and regards,
-- craig