intelligent selection of forwarders?

James Ralston qralston+ml.bind-workers at
Wed Aug 14 23:04:00 UTC 2002

The 4th edition of "DNS and BIND" contains this comment on forwarder
selection (page 270):

    On BIND 8.2.3 name servers, you don't need to list forwarders more
    than once.  These name servers don't necessarily query the
    forwarders in the order listed; they interpret the name servers in
    the list as "candidate" forwarders and choose which one to query
    first based on roundtrip time, the time it took to respond to
    previous queries.

    This is a real benefit if a forwarder fails, especially the first
    one in the list.  Older versions of BIND would keep blindly
    querying the failed forwarder and waiting before querying the next
    in the list.  BIND 8.2.3 quickly realizes that the forwarder isn't
    responding and tries another first.

    BIND 9 doesn't yet implement this more intelligent form of
    forwarder selection, unfortunately, though it will retransmit
    queries to forwarders when necessary.

(The last sentence of the first paragraph doesn't parse; I'm pretty
sure the word "then" was supposed to appear after the comma and before

Anyway, this was referring to BIND 9.1.0.  I was hoping that this
feature had been added since then, but the CHANGES file for BIND 9.2.1
doesn't mention it.

So, my question: what version of BIND 9 implements the more
intelligent forwarding?  If the answer is "none", then is there an
estimate when (as in, what version) this feature will be added?

James Ralston, Information Technology
Software Engineering Institute
Carnegie Mellon University, Pittsburgh, PA, USA

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