How to check slave zone freshness

[Mark Andrews]

In message <barmar-E66F2B.11060409022016 at 88-209-239-213.giganet.hu>, Barry Margolin writes:
> In article <mailman.193.1455032305.73610.bind-users at lists.isc.org>,
>  Klaus Darilion <klaus.mailinglists at pernau.at> wrote:
> 
> > On 08.02.2016 20:49, Mark Andrews wrote:
> > > With a modern nameserver that supports the expire edns option you can
> > > also do "dig +expire soa zone @server" which will tell you how long
> > > until the zone will expire on this server.
> > 
> > Aha, but isn't this a different kind of information? A zone which is not
> > fresh anymore (refresh interval expired and checks to the master failed)
> > may still be valid (not expired yet).
> 
> Subtract the time until expiry from the SOA Expire field, and that tells 
> you how long it has been since it last refreshed.

No.  EXPIRE is designed to handle xfr transfer graphs with loops.
While I haven't yet adjusted the expire timer based on the expire
option value in named it is something that is planned to be done.

With "master -> slave -> slave" both slaves will end up with the
same expire option value as the slaves will use min(soa expire,
max(current expire, edns expire option)) as the value to update the
expire timer with.  With this graph they will both get the same
value

         /- slave1 -\
master <             > slave3
         \- slave2 -/

The slave3 will be max of slave1 and slave2.

         /- slave1 -\
master <      |      > slave3
         \- slave2 -/

All three slaves will have a expire based on the most recent refresh
of slave1 and slave2 against master.

> -- 
> Barry Margolin
> Arlington, MA
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org