TCP Three-way Handshake and Four-way Teardown Demo
Visualize TCP three-way handshake and four-way teardown process to learn complete TCP connection establishment and termination
TCP Connection States
Handshake States
- LISTEN: Server waiting for connection
- SYN_SENT: Client has sent SYN
- SYN_RCVD: Server received SYN and sent SYN+ACK
- ESTABLISHED: Connection established
Teardown States
- FIN_WAIT_1: Client has sent FIN
- CLOSE_WAIT: Server received FIN
- FIN_WAIT_2: Client waiting for server FIN
- LAST_ACK: Server waiting for last ACK
- TIME_WAIT: Client waiting for timeout
- CLOSED: Connection closed
Half-Open Connection States
Half-open connections refer to intermediate states during TCP connection establishment, primarily including SYN_SENT and SYN_RCVD states. Connections in these states are not fully established and can be vulnerable to network attacks.
Common Half-Open Connection Issues
SYN Flood
SYN Flood Attack: Attackers send numerous SYN packets without completing handshakes, exhausting server resources
Server Not Responding
Server Not Responding: Server doesn't reply with SYN+ACK after receiving SYN, client remains in SYN_SENT state
Client Not Responding
Client Not Responding: Server doesn't receive ACK after sending SYN+ACK, server remains in SYN_RCVD state
Network Issues
Network Issues: Network latency or packet loss interrupts handshake process, connection remains in half-open state