关于一道Cisco的题目,哪位高手解释下?特别是subnet zero什么意思?

问题描述:

关于一道Cisco的题目,哪位高手解释下?特别是subnet zero什么意思?
Which three IP address can be assigned to hosts if the subnet mask is /27 and subnet zero is usable?(choose three)
A10.15.32.17
B 17.15.66.128
C 66.55.128.1
D 135.1.64.34
E129.33.192.192
F 192.168.5.63
答案是选择A C D 为什么求解释

在启了0子网,子网掩友为/27时哪三个IP地址可以分配给主机?
/27 = 255.255.255.224
块地址= 256-224=32
B/C是个网络地址
F是个广播地址.