howto: keep serving from cache after TTL if servers down ?

Wouter Wijngaards wouter at
Fri Nov 23 16:02:33 UTC 2018

Hi Sean,

On 23/11/2018 16:56, Sean Darcy via Unbound-users wrote:
> I'm running a voip application, asterisk, that dies if it can't
> resolve the addresses for its SIP registrations. Importantly there are
> other connections, PSTN, that work even if the internet connection is
> down. Also, I want the app to stay alive so that it can reconnect to
> the SIP servers once the internet comes back up. For whatever reason,
> asterisk itself will not have a fix for this.
> I have unbound working on the machine. I'd like to have unbound serve
> an address from its cache even if it's beyond the ttl IF it can't
> refresh the address. In other words, just serve the stale address
> until it can be refreshed.
> Any way to do this ?

serve-expired: yes in unbound.conf serves stale data.

It is good to also enable prefetch: yes.  Then unbound tries to refresh
data that is about to expire, whilst serving the existing data.

You can fine-tune it with the serve-expired-ttl and
serve-expired-ttl-reset options if you want.  But you can just leave
those at the defaults.

Best regards, Wouter

> sean

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