intelligent selection of forwarders?

Cricket Liu cricket at
Wed Aug 14 23:14:28 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 beg to differ.  The last phrase, "the time it took to respond to previous
queries," is what's called an appositive.  See:

> I'm pretty sure the word "then" was supposed to appear after the comma
> and before "the".)

No, it wasn't.

> 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?

The answer is none.  Maybe someone at Nominum can give you an
estimate of when the feature will be added.


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