### 规则
ip: 00001010.00010101.11100000.00000000 10.21.224.0
子网掩码: 11111111.11111111.11111100.00000000 255.255.252.0
网络标识: 11111111.11111111.11100000.00000000 10.21.224.0
ip: 00001010.00010101.11100000.00000000 10.21.224.0
子网掩码取反: 00000000.00000000.00000011.11111111 0.0.3.255
广播地址: 00001010.00010101.11100011.11111111 10.21.227.255
ip地址段 10.21.224.1~10.21.227.254
案例一、172.19.208.0/20
ip: 10101100.00010011.11010000.00000000
子网掩码: 11111111.1111111.11110000.00000000
网络标识: 10101100.00010011.11010000.00000000 (172.19.208.0)
ip: 10101100.00010011.11010000.00000000
子网掩码取反: 00000000.00000000.00001111.11111111
广播地址: 10101100.00010011.11011111.11111111 (172.19.223.255)
案例二、172.19.96.0/20
ip: 10101100.00010011.01100000.00000000
子网掩码: 11111111.1111111.11110000.00000000
网络标识: 10101100.00010011.01100000.00000000 (172.19.96.0)
ip: 10101100.00010011.01100000.00000000
子网掩码取反: 00000000.00000000.00001111.11111111
广播地址: 10101100.00010011.01101111.11111111 (172.19.111.255)
案例三、172.19.120.0/24
ip: 10101100.00010011.01111000.00000000
子网掩码: 11111111.1111111.11111100.00000000
网络标识: 10101100.00010011.01111000.00000000 (172.19.120.0)
ip: 10101100.00010011.01111000.00000000
子网掩码取反: 00000000.00000000.00000011.11111111
广播地址: 10101100.00010011.01111011.11111111 (172.19.123.255)