Packet Headers

• author:: Nathan Acks
• date:: 2021-08-11

Important/Common TCP Packet Headers

• Time to Live (TTL) - How long a packet should live on the network before being discarded.
• Source port - A random (unused) port chosen by the sender.
• Destination port - The port on the receiving end, which normally is determined by the application being used.
• Source address - “From” IP address.
• Destination address - “To” IP address.
• Sequence number - A random number that identifies a given connection.
• Acknowledgement number - Starts at the sequence number and then increases by the number of bytes received in the previous packet (or 1 is the previous packet did not include a data segment). Used to ensure that no data is lost, and that packets are reassembled in the right order.
• Checksum - Integrity check.
• Data - The, well, data.
• Flag(s) - How the packet should be handled (SYN, ACK, FIN, RST, etc.).

There’s potentially a lot more detail then this in a TCP packet header, however.

• 2022-08-11 — DEF CON 30

Important/Common UDP Packet Headers

• Time to Live (TTL) - How long a packet should live on the network before being discarded.
• Source port - A random (unused) port chosen by the sender.
• Destination port - The port on the receiving end, which normally is determined by the application being used.
• Source address - “From” IP address.
• Destination address - “To” IP address.
• Data - The, well, data.