A TCP handshake is a three-way exchange of messages between a client and a server to establish a TCP connection. The client initiates the handshake by sending a SYN packet with a sequence number to the server. The server responds with a SYN-ACK packet with its own sequence number and an acknowledgment number that is the client's sequence number plus one. The client completes the handshake by sending an ACK packet with an acknowledgment number that is the server's sequence number plus one. If the remote server is not receiving an SYN-ACK packet from the local server, it means that the TCP handshake is not completed and the connection is not established. This could be caused by various factors, such as network congestion, firewall rules, packet filtering, or misconfiguration of the TCP parameters on either end. Reference:= Understanding Cisco Cybersecurity Operations Fundamentals (CBROPS) - Cisco, page 177; TCP 3-Way Handshake Process - GeeksforGeeks