(DNS Overview DNS (DomainNameSystem) is a domain name system, which is a distributed database for TCP/IP applications. It provides conversion between host names (domain names) and IP addresses and routing information about e-mails. The number is 53. DNS uses the client server method. When a user process needs to map a host name to an IP address, the user process becomes a client of the domain name system DNS, and sends the domain name to be converted in a DNS request message to the local Domain Name Server. After the local domain name server looks up the domain name, it returns the corresponding IP address in the reply message. After using the process to obtain the IP address of the destination host, communication can be performed. The working principle of 2DNS A detailed example is used to illustrate the working process of DNS. As shown in Figure 1, first start the Rlogin client program, and then connect to an Rlogin server located in another domain. Figure 1 DNS work process 1) After the client program starts, it calls its name resolver function to convert the host name we type into an IP address, so a DNS query message is sent to a root server. 2) The response returned by the root server includes the name server name of the domain where the Rlogin server is located. 3) The name resolver of the client resends the above DNS query message to the name server of the Rlogin server. 4) The returned response includes the IP address of the Rlogin server)
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