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struct ipheader {
unsigned char ip_hl:4, ip_v:4;
unsigned char ip_tos;
unsigned short int ip_len;
unsigned short int ip_id;
unsigned short int ip_off;
unsigned char ip_ttl;
unsigned char ip_p;
unsigned short int ip_sum;
unsigned int ip_src;
unsigned int ip_dst;
}; /* total ip header length: 20 bytes (=160 bits) */

struct tcpheader {
unsigned short int th_sport;
unsigned short int th_dport;
unsigned int th_seq;
unsigned int th_ack;
unsigned char th_x2:4, th_off:4;
unsigned char th_flags;
unsigned short int th_win;
unsigned short int th_sum;
unsigned short int th_urp;
}; /* total tcp header length: 20 bytes (=160 bits) */

IP Header: h t t p://lxr.linux.no/linux+v3.1.2/include/linux/ip.h#L85
TCP Header: h t t p://lxr.linux.no/linux+v3.1.2/include/linux/tcp.h#L24

Hey Guys,
What about options field in IP header? IP header length can be from 20 bytes to 60 bytes... (that is why 4 bit varying header length field .)