TCP/IP Header Structure

// MAC header, total length 14 bytes Typedef struct _ eth_hdr {unsigned char dstmac [6]; // target MAC address unsigned char srcmac [6]; // source MAC address unsigned short eth_type; // Ethernet Type} eth_hdr; // IP header, total length: 20 bytes Typedef struct _ ip_hdr {# If little_endianunsigned char IHL: 4; // header length unsigned char version: 4, // version # else www.2cto.com unsigned char version: 4, // version unsigned char IHL: 4; // header length # endifunsigned char TOS; // service type unsigned short tot_len; // total length unsigned short ID; // flag unsigned short frag_off; // shard offset unsigned char TTL; // survival time unsigned char protocol; // protocol unsigned short chk_sum; // check and struct in_addr srcaddr; // source IP address struct in_addr dstaddr; // destination IP address} ip_hdr; // TCP Header, with a total length of 20 bytes Typedef struct _ tcp_hdr {unsigned short src_port; // source port number unsigned short dst_port; // destination port number unsigned int seq_no; // serial number unsigned int ack_no; // confirmation # If little_endianunsigned char reserved_1: 4; // retain the four-digit header length of the six-digit unsigned char Thl: 4; // TCP Header Length: unsigned char flag: 6; // The six-digit flag unsigned char reseverd_2: 2; // retain the two digits in the six digits # elseunsigned char Thl: 4; // The TCP Header Length unsigned char reserved_1: 4; // retain the four-digit header length of the six-digit unsigned char reseverd_2: 2; // retain the two-digit unsigned char flag: 6; // the six-digit sign # endifunsigned short wnd_size; // 16-bit window size unsigned short chk_sum; // 16-bit TCP test and unsigned short urgt_p; // 16 is an emergency pointer} tcp_hdr; www.2cto.com // UDP header, total length 8 bytes Typedef struct _ udp_hdr {unsigned short src_port; // remote slogan unsigned short dst_port; // destination port number unsigned short Uhl; // UDP header length unsigned short chk_sum; // 16-bit UDP check and} udp_hdr; // ICMP header, with a total length of 4 bytes Typedef struct _ icmp_hdr {unsigned char icmp_type; // type unsigned char code ;// Code Unsigned short chk_sum; // 16-bit check and} icmp_hdr;