IP address category

We have said that the Internet is a large inter-network that connects countless networks around the world. Computers in each network are uniquely identified by their own IP addresses. Therefore, we can imagine that, on the INTERNET, each network also has its own identifier.
This is very similar to the phone number in our daily life. For example, if a phone number is 0515163, the first four digits in the number indicate the region of the phone number, the following number indicates a telephone number in the region. Similar to the preceding example, we divide the IP address of a computer into two parts: 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 Workstation, server, and router, has a host ID corresponding to it? The four bytes of an IP address are divided into two parts. One part is used to indicate the specific network segment, that is, the network identifier; the other part is used to indicate the specific node, that is, the host identifier, that is, a specific computer number in a network. For example, the IP address of the server in Yancheng Information Network Center is 210.73.140.2. For this IP address, we can divide it into two parts: the network ID and the host ID, so that the above IP address can be written:

Network ID: 210.73.140.0

Host ID: 2

Write in combination: 210.73.140.2

Because there may be many computers in the Network, some networks may contain many computers, and some networks may contain fewer computers. Therefore, according to the size of the network, the 32-bit address information is divided into three positioning methods, which correspond to Class A, Class B, and class C IP addresses respectively.

1. Class a ip Address

A Class a ip address refers to the network number of the first segment of the four segments of the IP address, and the remaining three segments are the numbers of the local computer. If A binary IP address is used to represent an IP address, A Class a ip address consists of A 1-byte network address and A 3-byte host address. The maximum IP address must be 0 ". In Class a ip addresses, the network ID length is 7 bits, the host ID is 24 bits, and the number of class A network addresses is small. It can be used in large networks with hundreds of thousands of hosts.

2. Class B IP Address

A Class B ip address refers to the four segments of the IP address. The first two segments of the number are network numbers. The class B IP address consists of a 2-byte network address and a 2-byte host address, the maximum value of the network address must be "10 ". In type B ip addresses, the network ID length is 14 bits, and the host ID is 16 bits. Type B network addresses are suitable for medium-scale networks, each network can accommodate more than 60 thousand computers.

3. Class c ip Address

A Class c ip address refers to the network number in the four segments of the IP address, and the remaining segment is the number of the local computer. If the IP address is expressed in binary format, the class c ip address consists of a 3-byte network address and a 1-byte host address. The maximum network address must be 110 ". In Class c ip addresses, the network ID length is 21 bits, the host ID is 8 bits, and the number of class C network addresses is large, which is suitable for small-scale local networks, each network can contain up to 254 computers.

In addition to the above three types of IP addresses, there are also several special types of IP addresses, the TCP/IP protocol stipulates that all the addresses starting with "11110" in the first byte of the IP address are called multi-point broadcast addresses. Therefore, any IP address whose first byte is greater than 223 or less than 240 is a multicast address. The IP Address "0.0.0.0" for each byte is 0 corresponds to the current host; the IP address "255.255.255.255" for each byte in the IP address is the broadcast address of the current subnet. All IP addresses that use "11110" will be reserved for future use; the IP address cannot start with "127", 127.1.1.1 is used for loop testing, and the first six-digit Group of the network ID cannot be set to "0 ", "0" indicates the local network.

Related Articles]

• Analyze basic knowledge and basic operations of IP addresses in detail
  

• Anti-Black Step 1: reconnaissance and hiding of small IP addresses
  

• Security Management Network starts with IP Address