Overview DNS

Domain Name System (DNS) is a distributed database that maps domain names and IP addresses. It provides conversion between domain names and IP addresses. With the use of DNS, when users access the Internet, they can use easy-to-memory and meaningful domain names. Then the domain name server in the network resolves the domain names into correct IP addresses. DNS is categorized into static DNS and dynamic DNS.

Static domain name resolution is conducted through a static DNS table. In the static DNS table, domain names and IP addresses are mapped, and some frequently used domain names are added. When a client requests for the IP address of a domain name, the DNS server first searches static DNS table for the corresponding IP address. This improves the efficiency of domain name resolution.

Dynamic domain name resolution is implemented by querying the DNS. A DNS client sends a domain name resolution request to a DNS server. After the DNS server receives the domain name resolution request, it first determines whether the requested domain name is located in its authorized management sub-domain. If yes, it searches the database for the required IP address and then sends the query result to the client. If the domain name is not in the authorized management sub-domain, the DNS server starts a recursive resolution with other DNS server, and then it sends the resolution result to the client. Alternatively, it specifies the address of the next DNS server in the response packet to the DNS client. Then, the client sends another domain name resolution request to the domain name server. This is so called iterative resolution mode.