TPZ wrote:
Are there any options for Bind to configure timeout for DNS requests?
Short answer: not as far as I know.
Hopefully you understand that it's the DNS clients, and not BIND itself,
that implement the main timeout/retry strategy for a DNS query
transaction. Send a request, if it times out, try another resolver in
the resolver list, or retry the request. The main determinant of whether
a request succeeds or fails, therefore, in the face of slow or
unavailable upstream nameservers, is the client resolver's
configuration, not BIND's. The applications which call the resolver
routines on those clients, may also have their own timeout values, which
can sometimes be significantly shorter than what is set in the client
resolver. Therefore they will timeout the lookup request before the
client resolver would have abandoned it.
BIND itself will time out and fail over quickly -- on the order of
milliseconds -- between the nameservers it talks to. It will also keep
track, in its cache, of what nameservers are responding slowly, or which
are giving invalid answers, and de-prioritize or avoid nameservers in
those respective categories. So, in practical terms, it is "self-tuning"
over time, and in a way that is far more sophisticated than setting a
single "timeout" value could ever hope to accomplish.
- Kevin
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