A, B, Class C address and subnet mask learning notes

The IP address consists of 32 bits, divided into four segments, consisting of a network number and a host number. Also divided into a b C D e Five address, where a B class C address for distribution to the global network users, D E class is a special address.

1, Class A address 1.0.0.0 to 126.255.255.255

Only the first paragraph is the network number, and the remaining three paragraphs are the host number. In binary notation, there are 8 bits, or one byte is the network number, and 24 bits, or three bytes, are the host number. Therefore, the class A address is less network address, but can host the maximum number of 2 of the 24-bit minus 2 equals 16777214 hosts, (minus 2 is because the host number is 1 when the network broadcast address, all 0 means the network number, which is two special addresses) equal to the network address of the highest bit must be "0", the address range is represented by the binary: 00000001 00000000 00000000 00000000--01111110 11111111 11111111 11111111, which is 1.0.0.0 to 126.255.255.255. Subnet mask is 255.0.0.0

(The network address between a and Class B is 127.0.0.0 to 127.255.255.255. Where 127.0.0.0 is a reserved address,127.0.0.1 to 127.255.255.254 is a special address, it is a local loopback (loopback) address, a local loopback address, and does not belong to any one of the class address classes. It represents the local virtual interface of the device, so the default is to be considered an interface that will never go down. There are similar definitions in the Windows operating system, so it is usually possible to ping the local loopback address before the network card is installed. It is generally used to check whether the local network protocol, the basic data interface, etc. are normal. The main role of the local loopback address is two: one is to test the network configuration, can ping the 127.0.0.1 (usually used 127.0.0.1) to explain the network card and IP protocol installation is not a problem; another role is some server/ Client applications need to invoke resources on the server at run time, typically specifying the IP address of the server, but when the program is running on the same machine without another server, the server's resources can be installed on the machine, and the server's IP address is set to 127.0.0.1 can also be run. ）

127.255.255.255 for broadcast address

2.B class address 128.0.0.0 to 191.255.255.255

The first two paragraphs are the network number, the remaining two paragraphs are the host number. It can accommodate a host of 2 16 times minus 2 equals 65534 units. The highest bit of its address must be "10". The binary representation is: 10000000 00000000 00000000 00000000--10111111 11111111 11111111 11111111, which is 128.0.0.0 to 191.255.255.255. The last one is the broadcast address. The subnet mask is 255.255.0.0.

3. Class C address 192.0.0.0 to 223.255.255.255

The first three paragraphs are the network number, and the remaining section is the host number. Can accommodate the host for the 256-2=254 station. The C-Class address has many network addresses and is suitable for small-scale LANs. The highest bit of its network address must be "110" and the binary representation is: 11000000 00000000 00000000 00000000--11011111 11111111 11111111 11111111, That is 192.0.0.0 to 223.255.255.255. The last address is the broadcast address. Subnet mask is 255.255.255.0

4.D class address 224.0.0.0 to 239.255.255.255

The Class D IP address is historically called a multicast address (multicast address), or multicast. In Ethernet, a multicast address is named a group that should receive a grouping site in this network application. The highest bit of the multicast address must be "1110" and the binary representation is: 11100000 00000000 00000000 00000000--11101111 11111111 11111111 11111111, which is 224.0.0.0 to 239.255.255.255

5. Subnet mask

The subnet mask cannot exist alone, and is used in conjunction with an IP address.

Composition rule: consists of 0 and 1, the mask is through the binary and to mask the address of the host, not change the address of the network. So the network number on the left is 1, and the host number segment on the right is 0. The Class A address, it only the first paragraph is the network address, then its subnet mask only the top eight bits are 1, the remaining 24 bits are 0, that is: 255.0.0.0. Similarly, Class B address: 255.255.0.0 Class C Address: 255.255.255.0

A, B, Class C address and subnet mask learning notes