What is Name Server delegation?
Name Server delegation is the process of updating your domains name servers at the registry level.
e.g., when you first sign up with FASTDOT, you may be prompted to delegate your existing domain to our name servers which can be done at your domain name registrar:
ns1.fastdot.com ns2.fastdot.com ns3.fastdot.com
In physical terms, delegation is very similar to how a manager will delegate responsibility of tasks to his staff. The results are the same, however more than one person was involved in the process. The manager receives the request for work, passes on the responsibility to another member of staff and either the staff member or the manager returns with the work results. This is all on the proviso that the work the staff member does is actually correct and is what the original requester asked for (or that the requester actually asked for something that was valid in the first place!).
With DNS delegation, it is pretty similar. When the com name servers are asked for the place to find authority of the zone example.com, they often delegate this work off to separate name servers (in fact in the vast majority of cases, they do in fact delegate the response to other name servers). When you first register a domain, say our example.com domain, this is often done through a third party called a registrar. It is common practice by registrars to put in their name servers for the delegation and to serve a default zone from those name servers. This default zone includes the basic requirements to serve that zone on the internet (the SOA, NS and A records associated to those NS records).
Obviously if you yourself want to take control of the authority of the domain, you have to ask the registrar to delegate the domain to your nameserver instead. Different registrars refer to this in process in different ways, ‘change nameservers’, ‘use third party DNS’, ‘Add Glue records’ and so on. The mechanism underneath remains the same. You provide, generally, 2 or more “name server names” (for example ns0.example.com and ns1.example.com) and the IP addresses at which ns0 and ns1 are. They then process the request and the delegation is pointed away from your registrar to the nameservers you provided.
In technical terms, it’s at this point you have to ensure your nameservers are up and running, serving the domain example.com, with a minimum of an SOA (start of authority record), 1 or more NS records and the A records (the IPs) that these NS records are resolved from
Name Server Delegation
For a DNS server to answer queries about any name, it must have a direct or indirect path to every zone in the namespace. These paths are created by means of delegation. A delegation is a record in a parent zone that lists a name server that is authoritative for the zone in the next level of the hierarchy. Delegations make it possible for servers in one zone to refer clients to servers in other zones.
Recursive name resolution
Recursive name resolution is the process by which a DNS server uses the hierarchy of zones and delegations to respond to queries for which it is not authoritative.
In some configurations, DNS servers include root hints (that is, a list of names and IP addresses) that enable them to query the DNS root servers. In other configurations, servers forward all queries that they cannot answer to another server. Forwarding and root hints are both methods that DNS servers can use to resolve queries for which they are not authoritative.
Resolving names by using root hints
Root hints enable any DNS server to locate the DNS root servers. After a DNS server locates the DNS root server, it can resolve any query for that namespace. The following illustration describes how DNS resolves a name by using root hints.