DNS Negative Caching

[Reindl Harald]

Am 25.08.2015 um 12:46 schrieb Harshith Mulky:
> I have a confusion on how the clients respond to and cache when
> particularly we receive negative replies from a DNS Server, particularly
> NXDOMAIN or SERVFAIL responses
>
> on the DNS Zone file we have these records
> $ORIGIN e164.arpa.
> @   IN     SOA  picardvm2.e164.arpa. e164-contacts.e164.arpa.  (
>                                  2002022404 ; serial
>                                  3H ; refresh
>                                  15 ; retry
>                                  1w ; expire
> *3h* ; minimum
>                                 )
>
> so 3h is basically the amount of time clients are asked to cache
> negative results.
>
> Now on the client side at lwresd.conf, if I have
>
> max-ncache-ttl 300
>
> Will the client override the default 3h value sent as response from the
> DNS Sever for the zone e164.arpa

yes, that's the purpose of this setting

> How are Negative responses usually cached?

by TTL while in case of a SERVFAIL i am not sure if it get cached


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