Differences Between Recursion Desired and Recursion Available

Harshith Mulky harshith.mulky at outlook.com
Fri Oct 6 08:11:56 UTC 2017

Hello Experts,

I read this from RFC1035 about RD and RA Bits

RD Recursion Desired - this bit may be set in a query and is copied into the response if recursion supported by this Name Server. If Recursion is rejected by this Name Server, for example it has been configured as Authoritative Only, the response (answer) does not have this bit set. Recursive query support is optional.

RA Recursion Available - this bit is valid in a response (answer) and denotes whether recursive query support is available (1) or not (0) in the name server.

>From these, I understood, that in a query(at resolver) if RD bit is set(RD=1), and if a server is authoritative, it will set RA bit to 0 and send back a referral response for the resolver to continue the Referral Procedure. IF the server had supported Recursion, then it would have completed the Referral Procedure and set the RA bit to 1 and sent response to Resolver.

What I am not able to understand is, What would happen when resolver does not set Recursion Desired bit in the query it sends?

If Recursion is supported on the server, Would the server do the Referral Queries and set the RA bit while sending Response?

If Recursion is not supported on the server, Would the Referral Query fail from the resolver?

Please can anybody give any pointers in this case?



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