SYN
SYN is a control flag in the TCP protocol used to initiate a connection between two network devices. It is part of the three-step handshake process that ensures both devices synchronize their communication parameters before exchanging data.
The three steps of the handshake involve:
1. The client sends a TCP packet with the SYN flag set to initiate a connection.
2. The server responds with a packet containing both the SYN and ACK flags, indicating acknowledgment and synchronization.
3. The client sends an acknowledgment, completing the handshake and establishing the connection.
The SYN flag plays an essential role in setting up the sequence numbers for communication between devices. However, it can be exploited in a SYN flood attack, a type of denial-of-service attack where an attacker sends many SYN requests without completing the handshake, overwhelming the target system.
The full documentation on SYN and its role in TCP can be found in RFC 793 at https://www.rfc-editor.org/rfc/rfc793.txt.