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If I have a master zone which is configured not to send any NOTIFY's, can the slaves still query the master, check the serial and get a zone-transfer?

I thought there were 2 possibilities:

  • Master sends NOTIFY to slaves => Zone-Transfer happens

  • Slaves check periodically, and if the serial number changed => Zone-Transfer happens

chris
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  • I think your second situation might be more what happens when the slaves are not authoritative, with a low TTL, they will check your master and update if the record has been updated. – NickW Jun 06 '16 at 09:59

2 Answers2

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The original behavior is that slaves periodically perform a check that their zone data is current, based on comparing the SOA SERIAL field, with an interval specified in the SOA REFRESH field. If the slave's local data is old it will trigger a zone transfer (IXFR/AXFR).

In addition to this, if the master sends a notify message that will trigger this same check immediately.


Ie, if you disable notifications the slaves will still periodically check that they are up to date but you lose the near-instant updates that you would normally have.
Community
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Håkan Lindqvist
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The second situation you mention is standard DNS behavior, as any resolving server who is not the authoritative source will try and contact the master, or something in between with an authoritative unexpired record (though not the entire domain set unless requested).

NickW
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  • I think the question is about slave zones specifically? – Håkan Lindqvist Jun 06 '16 at 12:27
  • Yeah, 6 of one, half a dozen of the other.. – NickW Jun 06 '16 at 13:04
  • The answer seems to be about cache eviction based on rrset TTL in non-authoritative servers? Slaves are authoritative and operate based on parameters from SOA fields. Am I missing something? – Håkan Lindqvist Jun 06 '16 at 13:53
  • Not in that sense, just in the sense that the default behavior of resolving servers is close enough to that of authoritative non updated slaves to be equal in this situation (except that a slave would respond as authoritative). – NickW Jun 06 '16 at 14:47