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Consider the case of two master DNS servers, one serving as the master for the zone sales.example.com, the other serving marketing.example.com (ignore the implausibility of these being the actual zones, that isn't the point). Each of these two masters has a slave, that is:

  • master1 has slave1
  • master2 has slave2

I want master1 to be a slave of master2, in that zone updates for marketing get sent over to master1 (that is, those machines that use master1 for DNS can obtain query information for marketing.example.com).

Now, the question is, how should slave1 be updated (since it will be serving if master1 is out of commission)? Should master2 be the master of slave1? Or should master1, when receiving updates for the marketing zone, inform slave1?

In other words, should it look like this:

master2 --> master1 --> slave1

or

master2 --> (master1, slave1)

Joe
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1 Answers1

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Either configuration will work but Ron Aitchison, the author of the outstanding "Pro DNS and BIND" book finds master2 --> master1 --> slave1 confusing. See 4.2.1 But Slaves can also be Masters.

Mark Wagner
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    If I read `The definition of a slave server is simply that it gets its zone data via zone transfer, whereas a master gets its zone data from a local file system.` properly, the terminology for master and slave should really be applied to _the zone_ in question, not the DNS server itself. That would simplify things to say that `marketing.example.com` receives updates on `master1` and `slave1` via notifies (vs. local files). Hopefully I'm "getting it." – Joe May 31 '18 at 23:46
  • Yeah that's right. I suspect most name servers are either all master or all slave zones so we call the server itself a master or slave. The updates are actually received via the AXFR/IXFR protocol which is initiated by receiving a NOTIFY. (The slaves are actually free to AXFR/IXFR whenever they like.) – Mark Wagner Jun 01 '18 at 00:34
  • And note that, partially for being politically correct, primary/secondary is prefered over master/slave. This is of course per zone as the same nameserver can be primary for a zone and secondary for another at the same time. – Patrick Mevzek Jun 02 '18 at 18:09