子网掩码(subnet mask)又叫网络掩码、地址掩码、子网络遮罩，它是一种用来指明一个IP地址的哪些位标识的是主机所在的子网以及哪些位标识的是主机的位掩码。子网掩码不能单独存在，它必须结合IP地址一起使用。子网掩码只有一个作用，就是将某个IP地址划分成网络地址和主机地址两部分-Subnet mask (subnet mask) also known as the network mask, mask address, subnet mask, it is used to indicate which bits of an IP address identifies the host on the same subnet and which bits identify the host of bit masks. Subnet mask can not exist alone, it must be used in conjunction with an IP address. Subnet mask is only one role, that is, an IP address is divided into network and host addresses of two parts