Hurricane Electric based in the US provide a number of services to the internet. They are probably best known for Tunnel Broker however they also offer DNS hosting services. They do both primary (they host the DNS as the master) and slave zones. Sometimes known as backup DNS.
While hosting my own name server is great and gives me all the flexibility of the many DNS records often not provided by companies having it running only on Linode infrastructure is a single point of failure from a provider perspective (they are in different data centers). Having HE in the mix stops this and also makes for a good guide on how to setup slave DNS for any use case.
The process is really easy.
If you have not already done it add the following IP's to the allow-axfr-ips section of your PowerDNS configuration run:
Find and add the ip's as shown below:
service pdns restart
Next we need to add the PowerDNS servers to your zone by using the command
pdnsutil edit-zone example.com
example.com 3600 IN NS ns2.he.net example.com 3600 IN NS ns3.he.net example.com 3600 IN NS ns4.he.net example.com 3600 IN NS ns5.he.net
pdnsutil increase-serial example.com pdns_control notify example.com
Add the domain to he.net control panel using the "add a slave" option. Your master is your main server so if it was ns1.example.com this is the address you would enter.
Press add slave
Wait and you should see it pull the zone in within a few mintues.