范围0~15,但是可以用的主机地址为1~14
192.168.20.1
192.168.20.2
192.168.20.3
192.168.20.4
...
...
...
192.168.20.14
除掉192.168.20.0和192.168.20.15
192.168.20.15为广播地址
192.168.20.1一般为网关
192.168.20.0为网络地址
网络掩码为 11111111.11111111.11111111.11110000
跟IP地址 "&" ,就得出了这些IP地址
11111111.11111111.11111111.11110000 (255.255.255.240)
& 11000000.10101000.00010100.00000010 (192.168.20.2)
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11000000.10101000.00010100.00000010 (192.168.20.2)
192.168.20.0/28
192.168.20.1-192.168.20.30