Chris,
The terms "iterative resolution" and "recursive resolution" appear to
be in fairly common use, but they are not "classic" DNS lingo (e.g. don't
appear in RFC 1034 or 1035, or any of the major RFCs which followed). RFC 4697,
from 2006, is not a "major" DNS RFC, but it defined "iterative resolver" (as
part of the composite term "iterative resolver component") via the text "the
name server component of a recursive name server receives DNS queries and the
iterative resolver component sends queries". That RFC also uses the term
"recursive resolution algorithm", but, it appears, only as an umbrella term to
include *both* the "name server component" and "iterative resolver component",
in the previously-quoted text. So, it's not talking about the client, or the
client/server interface, only the algorithm that the server side follows.
The latest "terminology clarification" attempt
(https://tools.ietf.org/html/draft-ietf-dnsop-dns-terminology-05) is informed
by the iterative/recursive distinction, inasmuch as it defines the terms
"recursive mode", "recursive resolver", "recursive server", "iterative mode"
and "iterative resolver". But I think those definitions are still confusing,
because they don't squarely address the provider/consumer distinction -- an
entity which *provides* resolution for incoming RD=1 queries typically uses (on
its *consumer* side) RD=0 queries to get the answer; so, is it "recursive" or
"iterative" or *both*? RFC 4697's definition of an "iterative resolver" purely
in *consumer* terms ("sends queries"), is distinguished in this new draft only
in terms of the *provider* interface ("responds with a referral to another
server"). Also, the attempt, in that draft, to clarify "recursive server" talks
about it having a "name server side" and a "resolver side", but the term "name
server" is never actually defined in the document (amazingly!). I think I'll
raise these as problems with the draft.
Although it may seem like an oversimplification, the easy way to understand and
communicate this is that "iterative resolution" uses RD=0 queries and
"recursive resolution" uses RD=1 queries. (Whether the resolution attempt is
*successful* is another question, of course: sending an RD=1 query to a node
that doesn't honor recursion is likely to result in failure, but it can still
be said that the client *tried* to use "recursive resolution").
- Kevin
-Original Message-
From: Chris Buxton [mailto:cli...@buxtonfamily.us]
Sent: Thursday, November 19, 2015 11:33 AM
To: Darcy Kevin (FCA)
Cc: BIND Users
Subject: Re: does bind depends on system DNS settings for lookup?
On Nov 18, 2015, at 3:50 PM, Darcy Kevin (FCA) wrote:
> "Iterative" resolution means following the delegation hierarchy (by sending
> queries with the RD flag set to 0) to get an answer; "recursive" resolution
> means sending a query off (with the RD flag set to 1) and relying on the
> other party to get a complete answer back to you.
[…]
> The confusion comes in when it is stated that a DNS node provides "recursive
> service". What that means, is that, *as*a*provider*, the node receives and
> honors recursive queries from its clients, but *as*a*consumer*, it typically
> uses iterative resolution to get the answers. So it's essentially "recursive"
> on one side (queries come in with RD=1), "iterative" on the other (queries go
> out with RD=0). Once one understands the provider/consumer distinction,
> things become a lot clearer.
Kevin,
Where do these definitions come from? I don’t use those words in quite those
ways. I’ve thus far been unable to locate a definition of “recursive
resolution” or “iterative resolution” in the RFCs.
In the usage I’m used to, “iterative resolution” isn’t a thing; this phrase has
no defined meaning to me. What you’re describing here is what I’ve been calling
“recursive resolution”, or “recursion”.
What you’re describing as “recursive resolution” is actually just a “recursive
query” to my mind, a query asking for the server to perform the recursive
algorithm (“RD” = “recursion desired”). Recursion, or recursive resolution, is
the recursive algorithm that queries authoritative servers; each iteration of
this algorithm involves sending an iterative query.
I can find references in RFC 1034 to “recursive service”, which matches up with
my usage of the phrase “recursive resolution". I can also find “recursion”,
again matching my usage. The phrase “iterative service” in the RFC describes
the way a server handles a query if recursion is either not available or not
desired.
Regards,
Chris
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