Internet Naming Rules and Addressing Conventions

For us ordinary users, visual symbols are much easier to remember than a bunch of boring numerical codes. For example, we will easily remember the string "www.oscar.com", but it will be difficult to remember 206.17.191.12. This article briefly introduces Internet naming rules and address division conventions, and then introduces how to use Java language to complete the conversion between symbolic names (above string) and IP addresses (above numeric string), and gives an example , check the accessible remote hosts.

　Internet naming rules and address division conventions

　On the Internet, symbolic names are used to name hosts and networks, such as www.oscar.com. The "scientific name" of these symbolic names is called "Domain Name", which is the domain name. Although domain names are much more convenient for us, they must be converted into IP addresses (Internet Protocol Address) before they can be used as communication identifiers. An IP address is a 32-bit identifier that includes a network identifier and a host identifier to uniquely identify the host and network. The conversion of domain names into IP addresses is completed by a specialized system, which is the Domain Name System (Domain Name System??DNS). ?

　 When data is sent/received between hosts on the same network or different networks, the IP address comes into play. If the data is transferred between hosts on the same network, only the host identifier in the IP address is used to determine the location of the host on the network. On the other hand, if it is communication between hosts in different networks, both the host ID and the network ID must be used to determine the corresponding host. The process of locating the network and host and then transmitting data is called routing. The router in the network contains an IP layer, which is responsible for executing the routing algorithm and sending the data packets to the destination. On the Internet, sending a database to its destination is a matter of IP layer. ?

　 IP addresses are assigned to different organizations by the Internet registration department - Network Information Center (Network Information Center - NIC), and each organization then delegates it to multiple departments. An IP address takes up 4 bytes. ?

　 Routed data packets may also be lost during transmission. Therefore, people use the underlying transmission protocol to judge whether the data transmission is correct or not. For example, TCP is used to check for errors or data loss, and when an error occurs, the corresponding database is sent again until the other host receives it correctly. ?

Currently, there are 3 categories (or 3 levels) of IP addresses: Class A, Class B and Class C. In addition, there is a type of IP address called "Multicast", which is used on some Internet hosts. These different categories of IP addresses meet the needs of different organizations. For example, Class A addresses are mainly used for large network systems with more than 65536 hosts; Class B addresses are used for medium-sized network systems with more than 255 hosts but less than 65536; Class C addresses are used for small ones with less than 256 hosts. network. ?

The above introduces the Internet naming rules and address division conventions, including aspects of the content. I hope it will be helpful to friends who are interested in PHP tutorials.