Stub zones are a little like slave zones, in that the name server periodically checks with its master server to see if the zone’s serial number has changed. But instead of transferring the whole zone, it retrieves just the zone’s SOA and NS records, plus any necessary glue A records, using discrete queries. That’s enough information to tell the name server where to begin iterative name resolution of domain names that end in the domain name of the stub zone. For example, here’s a stub zone definition very similar to the forward zone :
zone "example.org" {
type stub;
masters { 10.10.10.20; };
file "example.org.zone";
};
Rather than sending a recursive query to the name server at 10.10.10.20 for information about any domain name that ends with example.org, this name server would learn the example.org NS records, and send one of those name servers a non recursive query for the domain name it needed. It would then follow any successive referrals to find the answer. This is less work for the name server at 10.10.10.20, but it also requires connectivity to any name server the local name server might be referred to.