typedef u_int32_t tcp_seq; struct tcp_header {	u_int16_t th_sport;		/* source port */	u_int16_t th_dport;		/* destination port */	tcp_seq	  th_seq;		/* sequence number */	tcp_seq	  th_ack;		/* acknowledgement number */#if BYTE_ORDER == LITTLE_ENDIAN	u_int8_t  th_x2:4,		/* (unused) */		  th_off:4;		/* data offset */#endif#if BYTE_ORDER == BIG_ENDIAN	u_int8_t  th_off:4,		/* data offset */		  th_x2:4;		/* (unused) */#endif	u_int8_t  th_flags;#define	TH_FIN	  0x01#define	TH_SYN	  0x02#define	TH_RST	  0x04#define	TH_PUSH	  0x08#define	TH_ACK	  0x10#define	TH_URG	  0x20	u_int16_t th_win;			/* window */	u_int16_t th_sum;			/* checksum */	u_int16_t th_urp;			/* urgent pointer */};struct ip_header {#if BYTE_ORDER == LITTLE_ENDIAN	u_int8_t  ip_hl:4,		/* header length */		  ip_v:4;		/* version */#endif#if BYTE_ORDER == BIG_ENDIAN	u_int8_t  ip_v:4,		/* version */		  ip_hl:4;		/* header length */#endif	u_int8_t  ip_tos;		/* type of service */	u_int16_t ip_len;		/* total length */	u_int16_t ip_id;		/* identification */	u_int16_t ip_off;		/* fragment offset field */#define	IP_RF 0x8000			/* reserved fragment flag */#define	IP_DF 0x4000			/* dont fragment flag */#define	IP_MF 0x2000			/* more fragments flag */#define	IP_OFFMASK 0x1fff		/* mask for fragmenting bits */	u_int8_t  ip_ttl;		/* time to live */	u_int8_t  ip_p;			/* protocol */	u_int16_t ip_sum;		/* checksum */	struct	  in_addr ip_src, ip_dst; /* source and dest address */};struct udp_header {	u_int16_t uh_sport;		/* source port */	u_int16_t uh_dport;		/* destination port */	u_int16_t uh_ulen;		/* udp length */	u_int16_t uh_sum;		/* udp checksum */};