IP地址的合法性及子网号的判断//判断IP地址是否合法//判断子网号是否合法//判断IP是否为子网成员，判断子网号与掩码是否匹配，以及子网号、主机号全0全1问题-Whether the IP address s validity and the subnet number s judgment does // judge the IP address legitimate // judgment subnet number whether legitimate // does judge IP whether is the subnet member, judgment subnet number and mask whether to match, as well as subnet number, main engine number entire 0 entire 1 question