Timeout and SERVFAIL

[Matus UHLAR - fantomas]

On 29.05.18 16:53, Alex wrote:
>I have a few fedora25 systems with bind-9.11 set up for a few domains.
>One system is master with the other two configured as slaves. The
>master and one of the slaves are on one network while the other slave
>is on a totally different network.
>
>Last week the network with the master and one of the slaves went down
>for an extended period. Requests appeared to still be served by the
>second slave on the totally different network.
>
>At least for a while. It appeared once the negative cache expired
>after 24h, requests to the domain just resulted in SERVFAIL.
>
>@  IN    SOA   ns.example.com. admin.ns.example.com. (
>                2018041703      ;serial (yyyymmddxx)
>                3h              ;refresh every 3 hr
>                1h              ;retry every 1 hr
>                7d              ;expire in 7 days
>                1d )            ;negative cache minimum ttl 1 day

I guess that the "extended period" was over 7 days, which is the "expire"
TTL. After this time, zone on the slave expired and the slave stopped
providing it, returning SERVFAIL.

Use longer expire times if you expect to experience this kind of problems
more often.

>How can I configure the name servers so failure of one or two doesn't
>impact the third?

Or use multiple master setup and distribute the zone differently than using
DNS mechanism.

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