RD is a Word property that indicates if recursive query support is desired on the DNS server responding to a DNS query. RD will contain the value 1 when recursive queries are desired on the name server, or the value 0 when recursive queries are not desired by the DNS resolver. 

Use RA to detgermine if recursive query support is available on a DNS server issuing a response. 

RD is represented in a DNS header as a bit field. Changing the value of RD ensures that the appropriate bit field is updated in the DNS header for the message packet.