Managing Mission - Critical Domains and DNS

The Refresh interval

This is how long your own secondary nameservers should wait before they check their master for an updated serial. This number should err on the side of longer, especially if the number of zones under management is large. If you have thousands, or hundreds of thousands, of zones under management and this interval is too short, you may end up with a bottleneck as at any given time you have a lot of SOA queries in progress for zones checking whether they have been updated.

Since the DNS NOTIFY transaction came along, we don't have to be so rigorous about polling. The master will let the slaves know when an update happens. If we are using an alternative nameserver, such as PowerDNS with database replication or tinydns copying ...