[NETWORK] Packet Header 의 구조.

IP Header 0   16   version -4 header length -4 type of service (TOS) -8 total length (byte) – 16 identification-16 flags-3 fragment offset-13 time to live(TTL)-8 protocol-8 header checksum-16 source IP address-32 destination IP address-32 options (if any) data   UDP Header 0 16 source port number-16 destination port number-16 UDP length-16 UDP checksum-16 data(if any)   TCP Header 0   16   source port number-16 destination port number-16 sequence number-32 acknowledgment number-32 header length-4 reserved -6 U R G A C K P S H R S T S Y N F I N window size-16 TCP checksum-16 urgent pointer-16 options (if any) data (if any)

 

 

/* eternet header */
 struct ether_header
 {
  u_char  dst_host[6];
  u_char  src_host[6];
  u_short  frame_type;
 }ether_header;

 

 

/* IPv4 header */

typedef struct ip_header
 {
  u_char ver_ihl;  // Version (4 bits) + Internet header length (4 bits)
  u_char tos;   // Type of service
  u_short tlen;   // Total length
  u_short identification; // Identification
  u_short flags_fo;  // Flags (3 bits) + Fragment offset (13 bits)
  u_char ttl;   // Time to live
  u_char proto;   // Protocol
  u_short crc;   // Header checksum
  ip_address saddr;  // Source address
  ip_address daddr;  // Destination address
  u_int op_pad;   // Option + Padding
 }ip_header;

 

 

 /* UDP header*/
 typedef struct udp_header
 {
  u_short sport;   // Source port
  u_short dport;   // Destination port
  u_short len;   // Datagram length
  u_short crc;   // Checksum
 }udp_header;

 

 

// 20 bytes TCP Header
typedef struct tcp_header

{
  u_short sport; // Source port
  u_short dport; // Destination port
  u_int seqnum; // Sequence Number
  u_int acknum; // Acknowledgement number
  u_char hlen; // Header length
  u_char flags; // packet flags
  u_short win; // Window size
  u_short crc; // Header Checksum
  u_short urgptr; // Urgent pointer...still don't know what this is...
}tcp_header;