forwarder selection logic by bind9

József Lázár jozsef.gabor.lazar at gmail.com
Tue Nov 13 09:42:34 UTC 2018


Ok, I see. However, could you please specify this "time to time" period?
Does it depends of the dns traffic which the bind receives?
I've tried the following scenario:
Configured two dns forwarders, both of them worked at the beginning. After
one minute I turned off the first dns forwarder and after an another minute
I restarted it.
Then I sent one dns request to bind in every 1,5 second for over one hour,
but the first dns server didn't receive any request after the restart.

Thanks, Joe

On Sun, 11 Nov 2018 at 15:06, Matus UHLAR - fantomas <uhlar at fantomas.sk>
wrote:

> On 10.11.18 15:59, József Lázár wrote:
> >I'm wondering what the selection logic in bind for forwarders. I tried to
> >look for this information in the official documentation but couldn't find
> >it. Could you please describe it for me briefly?
> >
> >Actually, the scenario is that I have two DNS servers and I'm using bind
> to
> >forward only the incoming DNS requests and if the "primary" one is failed
> >for a short period of time then the bind will try to use the "secondary"
> >one, but when the "primary" comes back, then it doesn't try to connect to
> >it at all, only if the connection breaks for the "secondary" server.
> >
> >Is there any way to configure this logic somehow?
>
> No. BIND technically choses server that responds faster. If one of servers
> doesn't respond (it's down), BIND uses the another one. However, time to
> time, BIND rechecks the other server(s) to see if situation has changed.
>
> BIND does not differ between servers as primary and secondary.
>
> --
> Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
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