TCP Socket States

Question 1

LISTEN

Answer 1

A TCP socket is ready and is listening for incoming connections. Server-side only.

Question 2

SYN_SENT

Answer 2

A synchronization request has been sent, but the connection hasn’t been established yet. Client-side only

Question 3

SYN_RECEIVED

Answer 3

A socket previously in a LISTEN state has received a synchronization request and has sent a SYN/ACK back. Server-side only

Question 4

ESTABLISHED

Answer 4

The TCP connection is in working order and both sides are free to send each other data. Seen on both Client and Server.

Question 5

FIN_WAIT

Answer 5

A FIN has been sent, but the corresponding ACK from the other end has not been received yet.

Question 6

CLOSE_WAIT

Answer 6

The connection has been closed at the TCP layer, but the application that opened the socket hasn’t released it’s hold on the socket yet.

Question 7

CLOSED

Answer 7

The connection has been fully terminated and no further communication is possible