TCP Example

TCP SYN-ACK

Analyze a TCP SYN-ACK packet, the second step of the three-way handshake. Understand how both SYN and ACK flags are set, acknowledgment numbering, and TCP header fields.

Hex Data

01 BB 00 14 00 00 00 01 00 00 00 02 50 12 08 00 20 00 00 00 00 00 00 00 00
Note: Both SYN and ACK flags set, acknowledgment number = SYN sequence number + 1
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handshakesyn-ack

Field Breakdown

Source Port
Source port number
443
HTTPS
Destination Port
Destination port number
20
FTP Data
Sequence Number
Sequence number of the first data byte in this segment
1
Acknowledgment Number
Next sequence number the sender expects to receive
2
Data Offset
Size of TCP header in 32-bit words (minimum 5, maximum 15)
80
Reserved
Reserved for future use (must be zero)
0b1010000
Flags
Control flags (NS, CWR, ECE, URG, ACK, PSH, RST, SYN, FIN)
0b101000000010010
Window Size
Size of the receive window (flow control)
2048
Checksum
Checksum for error detection
0x2000
Urgent Pointer
Offset from sequence number indicating last urgent data byte
0

Related Resources

TCP Protocol Visualizer - Parse & Analyze TCP PacketsTCP Header Format and Fields Explained - ByteLensTCP Three-Way Handshake Packet Breakdown | ByteLensTCP Flags Explained - SYN, ACK, FIN, RST, PSH, URGTCP SYN Packet Example - ByteLensTCP ACK Packet Example - ByteLens

About TCP

Transmission Control Protocol (RFC 793)

Fields: 10
Endianness: big
Specification: RFC 793