How to choose an authoritative name server

RTT: roundtrip time (roundtrip time)

When bind sends a query request to other name servers, an internal timer will start, and stop timing when a response is received, in order to record the time it takes for other name servers to respond (RTT).

When a name server must select one of a set of authoritative name servers for query, it will directly select the one with the least round-trip time. Before querying a name server, bind will randomly set a round-trip time for the name server. This value is smaller than any actual round-trip time. This ensures that the bind name server will query all authoritative name servers for a particular area in random order before getting the real round-trip time.

Resolution process:
1. The resolver accesses local dns
2. local dns iteratively queries
other dns servers 3. other dns servers try to direct local dns to the namespace 4. local
dns queries authoritative dns
5. local dns will update according to the response time of each other dns server and each authoritative dns server RTT value, which helps to decide which nameserver will be asked for future domain name resolutions