forwarders used in order or based on RTT ?

Victoria Risk vicky at
Mon Oct 19 15:26:20 UTC 2020

The ARM was updated in 9.16.6.  Sorry it took us so long!

Forwarders are typically used when an administrator does not wish for
all the servers at a given site to interact directly with the rest of
the Internet. For example, a common scenario is when multiple internal
DNS servers are behind an Internet firewall. Servers behind the firewall
forward their requests to the server with external access, which queries
Internet DNS servers on the internal servers' behalf.

Another scenario (largely now superseded by Response Policy Zones) is to
send queries first to a custom server for RBL processing before
forwarding them to the wider Internet.

There may be one or more forwarders in a given setup. The order in which
the forwarders are listed in ``named.conf`` does not determine the
sequence in which they are queried; rather, ``named`` uses the response
times from previous queries to select the server that is likely to
respond the most quickly. A server that has not yet been queried is
given an initial small random response time to ensure that it is tried
at least once. Dynamic adjustment of the recorded response times ensures
that all forwarders are queried, even those with slower response times.
This permits changes in behavior based on server responsiveness.


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