IPv4 classification

IPv4 addresses are divided into five categories

Class A

保留给政府机构
二进制形式，第一位总是0

• A Class 1 byte for the network address of the first address, the other three bytes for the host address. It is the first byte of the first bit is fixed to 0.
• Class A network number range address: 1.0.0.0 - 126.0.0.0
• Class A addresses are private addresses and reserved addresses:
  • 10.XXX is a private address
    范围：10.0.0.0 - 10.255.255.255 所谓的私有地址就是在互联网上不使用，而被用在局域网络中的地址
  • 127.XXX is reserved addresses, used cycle testing.

Class B

分配给中等规模的公司
二进制形式，第一位总是10

• Class B addresses 1 byte and 2 bytes for the network address, 2 bytes for the other host address. Its first byte 10 is fixed to the first two.
• Class B network address range number: 128.0.0.0 - 191.255.0.0
• Reserved addresses and private addresses Class B addresses
  • 172.16.0.0 - 172.31.255.255 is a private address
  • 169.254.XX is reserved address
    如果你的IP地址是自动获取IP地址，而你在网络上又没有找到可用的DHCP服务器。就会得到其中一个IP。
    191.255.255.255 is a broadcast address, can not be assigned

Class C

分配给任何需要的人
二进制形式，第一位总是110

• Class D

用于组播

• Class E

用于实验