In the checkdns.net example above, how does the DNS server 195.60.98.250 know what IP address to pass the authoritative DNS server? Firstly, look at what is static and what changes: Static: (a) IP addresses in the DNS recursor and (b) Authoritative name servers for Top-Level Domains. Non-static: Authoritative name servers for common domain names.

To register a domain name, a client must specify authoritative name servers to a registry. checkdns.net specifies name servers sigma.uniplace.com and orbiter.unipcorp.net to the .net registry. And to answer the question, when server 204.74.112.1 receives a request, the DNS server searches its list for checkdns.net and returns the specified name servers.

Name servers in delegations are listed by name, rather than by IP address. This means that a resolving name server must issue another DNS request to find out the IP address of the server to which it has been referred. Since this can introduce a bootstrapping problem when the name of the nameserver is in the domain about which nothing is yet known, it is occasionally necessary for the nameserver providing the delegation to also provide the IP address of the next nameserver. This record is called a glue record.