Zone delegation
When you register a domain, you specify its name servers — usually a pair like ns1.example.com and ns2.example.com. The parent zone (for example, the zone of a top-level domain) holds NS records that delegate the domain to those servers, and a resolver walking down the hierarchy uses them to learn who to ask for the A record and the rest of the data. Several NS servers are set for resilience: if one is unavailable, another serves the query.
Configuring on two levels
NS records need to be kept in sync in two places:
- At the registrar — this is where you set the name servers that go into the parent zone's delegation.
- Inside the zone itself — NS records are duplicated in the zone so they match the delegation.
- Caching — an NS change propagates slowly, bounded by the TTL of the delegation records.
Together with the NS records, a zone always begins with an SOA record, which stores service parameters and identifies the primary name server among those listed.
