TCP/IP header

Here is the full TCP/IP header:

Bytes	Description
0	bits 0-3: Version, bits 4-7: Internet Header Length (IHL)
1	Type of service (TOS)
2-3	Length
4-5	Identification
6-7	bits 0-3: Flags, bits 4-15: Offset
8	Time to live (TTL)
9	Type
10-11	Checksum
12-15	Source IP address
16-19	Destination IP address
20-IHL*4-1	Options + padding to round up to four bytes
0-1	Source Port
2-3	Destination Port
4-7	Sequence Number
8-11	Acknowledgement Number
12	bits 0-3: number of bytes of additional TCP Options / 4
13	Control
14-15	Window
16-17	Checksum
18-19	Urgent Pointer
20-20+Options*4	Options + padding to round up to four bytes
TCP Data begins at IHL*4+20+Options*4 and ends at Length-1