網(wǎng)絡(luò)協(xié)議結(jié)構(gòu)體

    // i386 is little_endian.   
    #ifndef LITTLE_ENDIAN   
    #define LITTLE_ENDIAN   (1)   //BYTE ORDER   
    #else   
    #error Redefine LITTLE_ORDER   
    #endif  

    //Mac頭部，總長(zhǎng)度14字節(jié)   
    typedef struct _eth_hdr  
    {  
        unsigned char dstmac[6]; //目標(biāo)mac地址   
        unsigned char srcmac[6]; //源mac地址   
        unsigned short eth_type; //以太網(wǎng)類(lèi)型   
    }eth_hdr;

 
    //IP頭部，總長(zhǎng)度20字節(jié)   
    typedef struct _ip_hdr  
    {  
        #if LITTLE_ENDIAN   
        unsigned char ihl:4;     //首部長(zhǎng)度   
        unsigned char version:4, //版本    
        #else   
        unsigned char version:4, //版本   
        unsigned char ihl:4;     //首部長(zhǎng)度   
        #endif   
        unsigned char tos;       //服務(wù)類(lèi)型   
        unsigned short tot_len;  //總長(zhǎng)度   
        unsigned short id;       //標(biāo)志   
        unsigned short frag_off; //分片偏移   
        unsigned char ttl;       //生存時(shí)間   
        unsigned char protocol;  //協(xié)議   
        unsigned short chk_sum;  //檢驗(yàn)和   
        struct in_addr srcaddr;  //源IP地址   
        struct in_addr dstaddr;  //目的IP地址   
    }ip_hdr; 

    //TCP頭部，總長(zhǎng)度20字節(jié)   
    typedef struct _tcp_hdr  
    {  
        unsigned short src_port;    //源端口號(hào)   
        unsigned short dst_port;    //目的端口號(hào)   
        unsigned int seq_no;        //序列號(hào)   
        unsigned int ack_no;        //確認(rèn)號(hào)   
        #if LITTLE_ENDIAN   
        unsigned char reserved_1:4; //保留6位中的4位首部長(zhǎng)度   
        unsigned char thl:4;        //tcp頭部長(zhǎng)度   
        unsigned char flag:6;       //6位標(biāo)志   
        unsigned char reseverd_2:2; //保留6位中的2位   
        #else   
        unsigned char thl:4;        //tcp頭部長(zhǎng)度   
        unsigned char reserved_1:4; //保留6位中的4位首部長(zhǎng)度   
        unsigned char reseverd_2:2; //保留6位中的2位   
        unsigned char flag:6;       //6位標(biāo)志    
        #endif   
        unsigned short wnd_size;    //16位窗口大小   
        unsigned short chk_sum;     //16位TCP檢驗(yàn)和   
        unsigned short urgt_p;      //16為緊急指針   
    }tcp_hdr; 

    //UDP頭部，總長(zhǎng)度8字節(jié)   
    typedef struct _udp_hdr  
    {  
        unsigned short src_port; //遠(yuǎn)端口號(hào)   
        unsigned short dst_port; //目的端口號(hào)   
        unsigned short uhl;      //udp頭部長(zhǎng)度   
        unsigned short chk_sum;  //16位udp檢驗(yàn)和   
    }udp_hdr; 

    //ICMP頭部，總長(zhǎng)度4字節(jié)   
    typedef struct _icmp_hdr  
    {  
        unsigned char icmp_type;   //類(lèi)型   
        unsigned char code;        //代碼   
        unsigned short chk_sum;    //16位檢驗(yàn)和   
    }icmp_hdr;