[troydavis]

A fair number of providers support zone transfers (AXFR requests) from master to slave name servers. The slaves can be operated by a different entity.

Here's DNSimple's implementation: https://support.dnsimple.com/articles/secondary-dns/

I wrote about moving from 1 to 2+ authoritative DNS providers: http://blog.papertrailapp.com/dns-outage-on-monday-december-.... I think this is just as true today:

> For .. maintainers of mission-critical DNS zones, the solution is to not depend on any single DNS infrastructure for functioning authoritative DNS