Slave zones not updating dynamically
The primary master name server determines which servers are the slaves for the zone by looking at the list of NS records in the zone and taking out the record that points to the name server listed in the MNAME field of the zone's SOA record as well as the domain name of the local host. Restarting a primary master name server causes it to notify all of its slaves of the current serial number of all of its zones because the primary master has no way of knowing whether its zone data files were edited before it started.
Reloading one or more zones with new serial numbers causes a name server to notify the slaves of those zones.
BIND 8 and 9 even have a provision for adding servers besides those in your zone's NS records to your "NOTIFY list." For example, you may have one or more unregistered slave name servers (described in Chapter 8, "Growing Your Domain") and you'd like them to pick up changes to the zone quickly.That kind of latency could wreak havoc in a dynamically updated environment.Wouldn't it be nice if the primary master name server could (the Unix file modification time) of all its zone data files to determine which had been changed, or it received and processed a dynamic update.The first remote has the highest preference, the other remotes are used for failover.When the server receives a zone update notification from a listed remote, that remote will be the most preferred one for the subsequent transfer.