IP address classification-How are IP address categories A, B, and C divided?

Today's IP networks use 32-bit addresses, represented in dotted decimal notation, such as 172.16.0.0. The address format is: IP address = network address + host address or IP address = Host address + subnet address + host address.

IP address type

In the initial design of the interconnected network, to facilitate addressing and hierarchical network construction, each IP address contains two ID codes, namely the network ID and host ID. All hosts on the same physical network use the same network ID. A host on the network (including Workstation, server, and router) has a host ID corresponding to it. IP addresses are divided into five types based on different network IDs: Class A address, Class B address, Class C address, Class D address, and Class E address.
1. Class a ip Address

A Class a ip address consists of a 1-byte network address and a 3-byte host address. The maximum network address must be "0" and the address range is from 1.0.0.0 to 126.0.0.0. There are 126 available class A networks, each of which can accommodate more than 0.1 billion hosts.

2. Class B IP Address

A Class B IP address consists of two bytes of network address and two bytes of host address. The highest bit of network address must be "10" and the address range is from 128.0.0.0 to 191.20.255. There are 16382 available class B networks, each of which can accommodate more than 60 thousand hosts.

3. Class c ip Address

A Class c ip address consists of a 3-byte network address and a 1-byte host address. The maximum network address must be 110 ". The range is from 192.0.0.0 to 223.20.255. A Class C network can contain more than 2.09 million hosts, and each network can accommodate 254 hosts.

4. Class D addresses are used for multicast ).

The first byte of A Class d ip address starts with "lll0". It is a reserved address. It does not point to a specific network. Currently, this type of address is used in multi-point broadcast (Multicast. A multicast address is used to address a group of computers at a time. It identifies a group of computers that share the same protocol.

5. Class e ip Address

Start with "llll0" and retain it for future use.

The zero ("0.0.0.0") Address corresponds to the current host. The IP address ("255.255.255.255.255") of "1" is the broadcast address of the current subnet.

In the three main types of IP addresses, each of the three regions is reserved as private addresses. The address ranges are as follows:

Class A address: 10.0.0.0 ~ 10.20.255.255

Class B address: 172.16.0.0 ~ 172.31.255.255

Class C address: 192.168.0.0 ~ 192.168.255.255

The first group of numbers of Class A addresses is 1 ~ 126. Note that numbers 0 and 127 are not class A addresses. Numbers 127 are reserved for the internal return function, while numbers 0 indicate that the address is a local host and cannot be transmitted.

The first group of B addresses is 128 ~ 191.

The first group number of class C addresses is 192 ~ 223.


1. Class A address

The expression range of Class A addresses is 0.0.0.0 ~ 126.255.255.255, the default network mask is 255.0.0.0; Class A addresses are allocated to large networks. In a network, the first group of numbers is used to represent the network address, and the last three groups of numbers are used as the addresses of hosts connected to the network. Assigned to a large network with a large number of hosts (direct individual users) and a small number of local networks. For example, the Network of an IBM company.

2. Class B address

The expression range of Class B address is 128.0.0.0 ~ 191.255.255.255, the default network mask is 255.255.0.0; Class B addresses are allocated to medium-size networks. Class B networks use numbers 1 and 2 to indicate network addresses. The latter two sets of numbers represent the host addresses on the network.

3. Class C address

The expression range of class C address is: 192.0.0.0 ~ 223.0000255, default network mask: 255.255.255.0; Class C addresses are allocated to small networks, such as local area networks and campus networks. The number of hosts that can be connected to is the minimum, users are managed by dividing their users into several network segments. The Class C network uses the first three sets of numbers to represent the network address, and the last set of numbers as the host address on the network.

In fact, there are still Class D addresses and Class E addresses. However, these two types of addresses are more useful than other addresses. Here we will just introduce them: Class D addresses are called broadcast addresses, which are used when special protocols send messages to selected nodes. Class E address is reserved for future use.