According to the current domain name rules, a complete domain name usually consists of two parts: the left part is an unrecognized universal prefix part composed of TCP/IP protocol type (such as Hypertext Network Protocol http) and World Wide Web code, and the right part is a domain name code part composed of top-level (level 1), level 2, level 3 or even level 4 domain names separated by periods in English, such as HYPERLINK "(Peking University domain name) and HYPERLINK". The right part of the last "."is called the code of top-level (first-level) domain name in a domain name, and the last "."on the left part is called the second-level domain name code, and the left part of the second-level domain name code is the third-level and fourth-level domain name codes respectively. On the whole, a domain name is composed of multilevel domain name codes that are degraded from right to left. The distinctiveness or identifiability of a domain name mainly comes from the registrant's own domain name code, such as the third-level domain name code pku in the hyperlink and the second-level domain name code microsoft in the hyperlink.