How to handle bind 9 as resolver on bad wireless links

Marc Haber mh+bind-users at zugschlus.de
Mon Aug 20 17:59:53 UTC 2007


Hi,

I am running a local bind9 on my notebook which is frequently
connected to the Internet via UMTS or GPRS while on a train. As you
might know, especially GPRS is famous for its abysmally high latency
and packet loss characteristics, which is supplemented by outages of
tens of seconds when the card is moving from one cell to another. In
this circumstances, I find it desireable to have a local DNS cache so
that network access does only fail when the "real" connection is made
and DNS reduces its role as a failure source.

Because the connectivity is so bad, I have bind misbehave though: When
it is resolving a recursive query, it keeps sending out the same query
over and over to a bundle of name servers. I suspect that the answers
that are (eventually) coming in are coming in too late for bind to
honor them, so the query goes out over and over.

This monopolizes the narrow upstream bandwidth that is available and
keeps other communication (for example the OpenVPN tunnel to my shell
host) from happening.

Is there any possibility to make bind

(1) wait longer for answers before resending a query?
(2) not send out a query to _this_ much hosts at once?
(3) be a little more careful with the bandwidth if there is not much
    bandwidth available?

Thanks for helping.

Greetings
Marc

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