Which timeouts are used by BIND when resolving recursive queries?

ip admin ipmanx at googlemail.com
Fri Oct 5 14:13:24 UTC 2018


Hi,

 I understand that I can configure a global timeout for resolving recursive
queries (resolver-query-timeout) but find that I cannot configure the
timeout for an individual query used during DNS resolution.

 For testing I configured one unreachable forwarder (and enabled forward
only) and saw (tcpdump) that BIND (9.10.6-P1) is first trying two queries
with EDNS which each seems to have a timeout of 1.2s. Afterwards queries
without ENDS are sent which seem to have a timeout of 1.6s, then 3.2s, then
6.4s, then 9s, finally the maximum (=total) resolver-query-timeout of 30s
is reached.

 Is the timeout behaviour documented anywhere (similar to a stub resolver
or dig, i.e. how long are timeouts, how many tries per server etc).

 If someone did find a logging setting that shows which servers are used
when recursing (forwarding or delegations) to find a response (and when the
individual queries time out) that would be helpful as well.

Regards
 Tom
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