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TASK

Parse TCP segment headers

TCP headers contain source/destination ports, sequence numbers, flags, and window size. Learn to decode TCP headers for network analysis.

  1. 1

    A TCP header is 20-60 bytes. Fields: source port (2 bytes), dest port (2 bytes), sequence number (4), acknowledgment number (4), data offset + flags (2), window size (2), checksum (2), urgent pointer (2), options (0-40). Flags: SYN, ACK, FIN, RST, PSH, URG, ECE, CWR.

  2. 2
    Hex Decoder →

    Decode the hex representation of a TCP header. The first 4 bytes are source and destination ports. For example, 0x0050 is port 80 (HTTP). Decode each field according to its offset and size.

  3. 3
    Binary Decoder →

    Decode the flags byte in binary. Each bit represents a flag: FIN (0x01), SYN (0x02), RST (0x04), PSH (0x08), ACK (0x10), URG (0x20). SYN+ACK = 0x12 = 00010010 in binary. This reveals the connection state.

Frequently asked questions

What do the TCP flags mean?
SYN: synchronize sequence numbers (connection start). ACK: acknowledgment number is valid. FIN: finish (graceful close). RST: reset (abort connection). PSH: push data immediately. URG: urgent pointer is valid. The combination of flags indicates the connection phase (SYN, SYN-ACK, ACK for handshake).
What is the TCP window size?
It indicates how many bytes the receiver can accept without acknowledgment — flow control. A larger window means higher throughput (less waiting for ACKs). Window scaling (RFC 7323) allows windows larger than 65535 by using a scale factor in the options.

Workflows that solve this

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Hex encode then decode round-trip
Encode text to hexadecimal and decode it back to verify the round-trip preserves the original data.
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Convert Hex to Base32
Decode hex and re-encode as Base32 for DNS-safe use.
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Convert Hex to Base64
Decode a hexadecimal string into raw bytes and re-encode it as Base64 for compact transport.
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Learn more

Want to understand why?

How to Convert Hex to Binary
Convert hexadecimal strings to binary representation and understand the relationship between the two.
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Deploy DNS Security Extensions (DNSSEC) to authenticate DNS responses with cryptographic signatures, preventing DNS spoofing and cache poisoning.
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Base16
Base16 is hexadecimal encoding: every 4 bits map to one hexadecimal character (0-9, A-F), making it the simplest member of the Base family defined by RFC 4648.
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Hexadecimal
Hexadecimal (hex) is the base-16 numeral system, using 0-9 and A-F for 0-15; it is one of the most common radix notations in computing.
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