Internet address Overview

All terminal devices connected to the Internet (including computers, PDAs, printers, and other electronic devices) have a unique index called an IP address. Currently, most IP addresses on the Internet are composed of four bytes, which are called IPv4. In addition to the four-byte IP address, there is also an IP address on the Internet, which consists of 16 bytes, called IPv6. The numbers after IPv4 and IPv6 are the version numbers of Internet protocol (IP.

The IPv4 address is generally expressed as x. x. X is an integer ranging from 0 to 255. The four integers are separated. Theoretically, an IPv4 address can represent the power of 2, that is, 4,294,967,296 IP addresses, however, to exclude some special IP addresses (such as 0.0.0.0, 127.0.0.1, 224.0.0.1, and 255.255.255.255, the number of IP addresses that an IPv4 address can allocate is smaller than the number of IP addresses that it can represent.

For ease of management, IPv4 is artificially divided into Class A, Class B, and class C IP addresses:

• Class a ip Address: The value range is 0.0.0.0 -- 127.255.255.255. The standard subnet mask is 255.0.0.0.
• Class B IP Address: The value range is 128.0.0.0 -- 191.255.255.255. The standard subnet mask is 255.255.0.0.
• Class c ip Address: The value range is 192.0.0.0 -- 223.255.255.255. The standard subnet mask is 255.255.255.0.

From the above description, we can see that the first byte between 0 and 127 is a Class a ip address, and the first byte between 128 and 191 is a Class B IP address, the C-class IP address is between 192 and 223. If the bitwise of the two IP addresses and Their subnet masks are the same as the obtained values, the two IP addresses are in the same network segment. The following are two class c ip addresses, IP1 and ip2, and their subnet masks.

IP1: 192.168.18.10 subnet mask: 255.255.255.0
Ip2: 192.168.18.20 subnet mask: 255.255.255.0

The bitwise AND values of the two IP addresses and Their subnet masks are 192.168.18.0. Therefore, IP1 and ip2 are in the same network segment. When a user uses a modem or ADSL modem to access the Internet, the IP address temporarily allocated to the local machine is generally a class C address, that is, the first byte will be between 192 and 223.

The IP address and subnet mask provided above are only in the standard format. You can also use other IP addresses and subnet masks as needed. For example, set the IP address to 10.0.0.1 and the subnet mask to 255.255.255.128. To facilitate classification and management, we recommend that you set IP addresses based on standard classification when setting IP addresses in the LAN.

An IPv6 address consists of 16 bytes and consists of 8 segments. Each segment consists of 2 bytes and is expressed in 4 hexadecimal notation. segments and segments are separated. For example, a34e: dd3d: 1234: 4400: A123: B231: a111: ddaa is a standard IPv6 address. IPv6 can be abbreviated:

• Segments starting with 0 can be omitted. For example, a34e: 003d: 0004: 4400: A123: B231: a111: ddaa can be abbreviated as a34e: 3D: 4: 4400: A123: B231: a111: ddaa.
• You can use ":" To replace multiple 0 segments. For example, a34e: 0000: 0000: 0000: A123: B231: 0: ddaa can be abbreviated as a34e: A123: B231: 0: ddaa. When you use this short form, ":" can only appear once. If it appears multiple times, the IPv6 address will be ambiguous.

In an IPv4-IPv6 hybrid network, the last four bytes of an IPv6 address can be written as an IPv4 address. For example, a34e: A123: B231: a111: ddaa can be written as a34e: A123: B231: 161.17.221.170. When the computer accessing network resources uses an IPv4 address, the system automatically uses the last four bytes of IPv6 as the IPv4 address.

Both IPv4 and IPv6 addresses are hard to remember. Therefore, in order to make these addresses easier to remember, Internet designers have invented the Domain Name System (DNS) domain [d domains (Domain Name System) 'Me domains N] domain name ). DNS is composed of a parser and a Domain Name Server. A Domain Name Server is a server that stores the domain names and corresponding IP addresses of all hosts in the network and converts a domain name to an IP address. The domain name must correspond to one IP address, and the IP address does not necessarily correspond to only one domain name. On the Internet, domain names and IP addresses are one-to-one (or multiple-to-one). DNS round robin can also be used to implement one-to-many domain names. Although domain names are easy to remember, only IP addresses are recognized between machines, the conversion between them is called domain name resolution. domain name resolution needs to be completed by a dedicated domain name resolution server, and DNS is the server for domain name resolution.

DNS associates IP addresses with Domain Names (a string that is easy to remember, such as Microsoft). When a computer accesses Internet resources through a domain name, the system first obtains the IP address corresponding to the domain name through DNS, access Internet resources through IP addresses. In this process, IP addresses are completely transparent to users. If a domain name corresponds to multiple IP addresses, DNS randomly selects one from these IP addresses and returns the result.

Domain names can be divided into different levels, such as top-level domain names, top-level domain names, second-level domain names, and third-level domain names.