点对点ping主机typedef struct icmp_hdr { unsigned char icmp_type; // 消息类型 unsigned char icmp_code; // 代码 unsigned short icmp_checksum; // 校验和 // 下面是回显头 unsigned short icmp_id; // 用来惟一标识此请求的ID号,通常设置为进程ID unsigned short icmp_sequence; // 序列号 unsigned long icmp_timestamp;