Classification of IP addresses

When the Internet was originally designed, in order to facilitate addressing and hierarchical network construction, each IP address included two identification codes (ID), namely the network ID and the host ID. All hosts on the same physical network use the same network ID. A host on the network (including workstations, servers, routers, etc.) on the network has a host ID corresponding to it. The Internet Committee has defined 5 IP address types to suit networks of different capacities, namely Class A ~ Class E.

Class A IP address (Recommended learning: PHP video tutorial)

An A A class IP address means that among the four segments of the IP address, the first segment is the network number, and the remaining three segments are the local computer numbers. If the IP address is represented in binary, the Class A IP address consists of a 1-byte network address and a 3-byte host address. The highest bit of the network address must be "0". The length of the network identifier in a Class A IP address is 8 bits, and the length of the host identifier is 24 bits. The number of Class A network addresses is relatively small, with 126 networks, and each network can accommodate more than 16 million hosts.

Class A IP address, address range 1.0.0.1 to 127.255.255.254 (binary representation: 00000001 00000000 00000000 00000001 - 01111111 11111111 11111111 11111110). The last one is the broadcast address.

The subnet mask of Class A IP address is 255.0.0.0, and the maximum number of hosts supported by each network is 256 to the third power -2=16777214.

Class B IP address

A Class B IP address means that among the four numbers in the IP address, the first two numbers are network numbers. If the IP address is represented in binary, the Class B IP address consists of a 2-byte network address and a 2-byte host address. The highest bit of the network address must be "10". The length of the network identifier in the Class B IP address is 16 bits, and the length of the host identifier is 16 bits. Class B network addresses are suitable for medium-sized networks. There are 16,384 networks, and each network can accommodate more than 60,000 computers. tower.

Class B IP address range 128.0.0.1-191.255.255.254 (binary representation: 10000000 00000000 00000000 00000001----10111111 11111111 11111111 11111110). The last one is the broadcast address.

The subnet mask of Class B IP address is 255.255.0.0, and the maximum number of hosts supported by each network is 256 to the power of 2-2=65534.

Class C IP address

A Class C IP address means that among the four numbers in the IP address, the first three numbers are network numbers, and the remaining A number is the number of the local computer. If the IP address is represented in binary, the Class C IP address consists of a 3-byte network address and a 1-byte host address. The highest bit of the network address must be "110". The length of the network identifier in a Class C IP address is 24 bits, and the length of the host identifier is 8 bits. There are more Class C network addresses, with more than 2.09 million networks. Suitable for small-scale local area networks, each network can only contain up to 254 computers.

Class C IP address range 192.0.0.1-223.255.255.254 (binary representation is: 11000000 00000000 00000000 00000001 - 11011111 11111111 11111111 11111110).

The subnet mask of Class C IP address is 255.255.255.0, and the maximum number of hosts supported by each network is 256-2=254

Class D IP address

Class D IP addresses were historically called multicast addresses, that is, multicast addresses. In Ethernet, a multicast address names a set of stations on the network that should receive a packet. The highest bit of the multicast address must be "1110", ranging from 224.0.0.0 to 239.255.255.255.

Class E IP address:

is a reserved address. The beginning of this type of IP address is "1111", so the network number of the address ranges from 240 to 255.

Special URL

An address where each byte is 0 ("0.0.0.0") corresponds to the current host;

IP address The IP address in which each byte is 1 ("255.255.255.255") is the broadcast address of the current subnet;

Any IP address starting with "11110" is a Class E IP The addresses are reserved for future and experimental use.

The IP address cannot start with decimal "127". The numbers 127.0.0.1 to 127.255.255.255 in this type of address are used for loop testing. For example, 127.0.0.1 can represent For the IP address of this machine, use "http://127.0.0.1" to test the Web server configured in this machine.

The first 6-bit group of the network ID cannot be set to all "0". All "0" indicates the local network.

For more PHP related technical articles, please visit the PHP Graphic Tutorial column to learn!

The above is the detailed content of Classification of IP addresses. For more information, please follow other related articles on the PHP Chinese website!