Test and development of network articles-IP address

The IP address is a unified address format provided by the IP protocol. It assigns a logical address to each network and each host on the Internet to shield the differences in physical addresses. Here is an introduction to the currently widely used version of IPv4.

The IP address uses a unified format to assign a logical address to every network and every device on the Internet. The IP address is a 32-bit binary number. For easy viewing, it is usually divided into 4 groups. The 8 bits of each group are expressed by a decimal number to form an address in the form of 192.168.0.10.

The IP address is composed of two parts, a network ID and a host ID. The two parts are distinguished by a subnet mask. Therefore, a complete IP address must include the host address and the subnet mask to make sense. It can be expressed in the following two forms:

192.168.0.10主机地址 和 255.255.255.0子网掩码：Windows中配置网络地址时，会要求您同时输入这两个值；
192.168.0.10/24：24表示子网掩码的二进制位数。对应的10进制分组表示为255.255.255.0。这里显示了3个十进制的255，简单换算关系为24（二进制位数） / 8（ 每组8位）= 3（分组数）。

Perform a binary AND operation on the host address and the subnet mask to get the network ID. If you are not familiar with binary arithmetic, you can simply mask the corresponding mask part of the IP address as 0. For example, the IP address of class C 192.168.1.10 uses the subnet mask 255.255.255.0 to shield the fourth group, and the network ID of the host is 192.168.1.0.

It should be noted here that the value of each group of the subnet mask does not have to be exactly 255 or 0. 255.255.12.0 is also a legal subnet mask.

People have defined three types of addresses, A, B, and C. The subnet masks are as follows.

A类：255.0.0.0
B类：255.255.0.0
C类：255.255.255.0

A range of private IP addresses is also defined, specifically for internal use by organizations.

A类：10.0.0.0~10.255.255.255 即10.0.0.0/8
B类：172.16.0.0~172.31.255.255即172.16.0.0/12
C类：192.168.0.0~192.168.255.255 即192.168.0.0/16

These are also the addresses you see the most in the company. Different organizations can use the same private address. This is because the internal network of the enterprise is isolated from the Internet and forwarded through routers. The private address is not directly exposed to the public network.

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