What information is exchanged during a TCP three-way handshake?

The TCP three-way handshake establishes a reliable connection between two hosts. During this process:

SYN: The client sends a TCP segment with the SYN flag set, including an initial sequence number (ISN) and port information.

SYN-ACK: The server responds with a SYN-ACK, which contains its own sequence number and acknowledgment of the client’s ISN.

ACK: The client replies with an ACK, confirming receipt of the server’s ISN.

Thus, port numbers (to identify the application endpoints) and sequence numbers (to ensure ordered and reliable data transfer) are exchanged.

Interfaces and application names are not exchanged during this process.

From Junos OS Fundamentals / TCP Concepts:

“The TCP three-way handshake establishes a reliable session by exchanging port numbers and sequence numbers between peers. This process synchronizes both sides before data transmission begins.”