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|
TCP Header | |||||||||||||||||||||||||||||||
| Bit Number |
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 1 0 | 1 1 | 1 2 | 1 3 | 1 4 | 1 5 | 1 6 | 1 7 | 1 8 | 1 9 | 2 0 | 2 1 | 2 2 | 2 3 | 2 4 | 2 5 | 2 6 | 2 7 | 2 8 | 2 9 | 3 0 | 3 1 |
| Source Port | Destination Port | ||||||||||||||||||||||||||||||
| Sequence Number | |||||||||||||||||||||||||||||||
| Acknowledgment Number | |||||||||||||||||||||||||||||||
| Offset | Reserved | Flags | Window | ||||||||||||||||||||||||||||
| Checksum | Urgent Pointer | ||||||||||||||||||||||||||||||
| Options (optional) | |||||||||||||||||||||||||||||||
| TCP Header Contents |
| Common TCP Well-Known Server 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 on 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) | ||
| Flags (UAPRSF) | ||
| U | (1 = Urgent pointer valid) | |
| A | (1 = Acknowledgement field value valid) | |
| P | (1 = Push data) | |
| R | (1 = Rest 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 | Windows scale | |
| 1 | No operation (pad) | 4 | Selective ACK ok | |
| 2 | Maximum segment size | 8 | Timestamp | |