SYN-ACK is a combination of the SYN (synchronize) and ACK (acknowledgment) flags in the Transmission Control Protocol (TCP) header. It plays a crucial role in the TCP three-way handshake, which is used to establish a connection between a client and a server.
Here’s a brief breakdown of how SYN-ACK fits into the TCP three-way handshake process:
- SYN: A client wanting to start a TCP connection with a server sends a TCP segment with the SYN flag set. This indicates its intent to establish a connection. Along with the SYN flag, the client also sends an initial sequence number.
- SYN-ACK: In response to the client’s SYN request, the server replies with a segment that has both the SYN and ACK flags set. The ACK flag acknowledges the receipt of the client’s SYN, while the SYN flag indicates the server’s sequence number and its readiness to establish a connection.
- ACK: The client then sends a segment with the ACK flag set back to the server, acknowledging the server’s SYN-ACK response. Once this step is completed, a TCP connection is established, and data transfer can commence.
In summary, the SYN-ACK is the server’s way of saying, “I received your request to establish a connection, and I’m also ready to establish that connection.”