[thefarseeker]

Author here. I agree. There are built-in mechanisms for doing this - AXFR and IXFR. However, these mechanisms were not really designed with this sort of scale in mind. You have to keep an up to date whitelist of all the servers that can talk to each other, and they would need to talk to each other on a non-anycasted address (otherwise the notify packet would go to just a single anycasted node).

Managing whitelists between multiple 3rd party DNS providers is likely to break frequently as servers move around, are added, removed, etc.

Interestingly, Hurricane Electric would have been one of our top choices if they had a first class API and a commercial SLA. Their ability to support zone transfers is admirable and did not go un-noticed. DNS Made Easy also supports zone transfers.

[jlgaddis]

Just as an additional data point for anyone else reading this...

Hurricane Electric supports zone transfers and requires you to only allow AXFR's from a single host -- slave.dns.he.net (IPv4: 216.218.133.2, IPv6: [2001:470:600::2]). NOTIFYs should not be sent to slave.dns.he.net but instead to ns1.he.net.

n.b.: ns1.he.net is not anycasted, but ns[2-5] are. In addition, ns1 does not have an AAAA RR.

We (ISP) currently run our own authoritative name servers in our own facilities but I've been seriously debating adding another provider into the mix so "secondary" service is an important feature to me.