| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Source Port | Destination Port | ||||||||||||||||||||||||||||||
| Sequence Number | |||||||||||||||||||||||||||||||
| Acknowledgment Number | |||||||||||||||||||||||||||||||
| Offset | Reserved | Flags | Window Size | ||||||||||||||||||||||||||||
| Checksum | Urgent Pointer | ||||||||||||||||||||||||||||||
| Options (optional) | |||||||||||||||||||||||||||||||
TCP Header Contents
Common TCP Well-Known Sever Ports 7 echo 110 pop3 19 chargen 111 sunrpc 20 ftp-data 119 nntp 21 ftp-control 139 netbios-ssn 22 ssh 143 imap 23 telnet 179 bgp 25 smtp 389 ldap 53 domain 443 https (ssl) 79 finger 445 microsoft-ds 80 http 1080 socks Offset Number of 32-bit words in TCP header; minimum value = 5 Reserved 4 bits; set to 0 ECN bits (used when ECN employed; else 00) CWR (1= sender has cut congestion window in half) ECN-Echo (1= receiver cuts congestion window in half) Flag (UAPRSF) U (1 = Urgent pointer valid) A (1 = Acknowledgement field value valid) P (1 = Push data) R (1 = Reset connection) S (1 = Synchronize sequence numbers) F (1 = no more data; Finish connection) Checksum covers pseudoheader and entire TCP segment Urgent Pointer Points to the sequence number of the byte following urgent data. Options 0 End of Options list 3 Window scale 1 No operation (pad) 4 Selective ACK ok 2 Maximum segment size 8 Timestamp