[리눅스] netstat 명령어

netstat 명령어

netstat - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships

netstat 상태(State)

state	description
ESTABLISHED	The socket has an established connection.
SYN_SENT	The socket is actively attempting to establish a connection.
SYN_RECV	A connection request has been received from the network.
FIN_WAIT1	The socket is closed, and the connection is shutting down.
FIN_WAIT2	Connection is closed, and the socket is waiting for a shutdown from the remote end.
TIME_WAIT	The socket is waiting after close to handle packets still in the network.
CLOSE	The socket is not being used.
CLOSE_WAIT	The remote end has shut down, waiting for the socket to close.
LAST_ACK	The remote end has shut down, and the socket is closed. Waiting for acknowledgement.
LISTEN	The socket is listening for incoming connections. Such sockets are not included in the output unless you specify the --listening (-l) or --all (-a) option.
CLOSING	Both sockets are shut down but we still don't have all our data sent.
UNKNOWN	The state of the socket is unknown.

 

출처-https://www.ictshore.com/wp-content/uploads/2016/12/1017-01-TCP_States_diagram.png

 

TCP endpoints state transmission

이미지 출처-https://totozhang.github.io/2016-01-23-tcp-connection-status-transit/TCPState2.png

tcp flags

state	description
SYN (synchronize)	Packets that are used to initiate a connection.
ACK (acknowledgment)	Packets that are used to confirm that the data packets have been received, also used to confirm the initiation request and tear down requests
RST (reset)	Signify the connection is down or maybe the service is not accepting the requests
FIN (finish)	Indicate that the connection is being torn down. Both the sender and receiver send the FIN packets to gracefully terminate the connection
PSH (push)	Indicate that the incoming data should be passed on directly to the application instead of getting buffered
URG (urgent)	Indicate that the data that the packet is carrying should be processed immediately by the TCP stack

출처-https://www.ictshore.com/wp-content/uploads/2016/12/1017-02-TCP_States_in_a_connection.png

performance diagram

출처-https://i.stack.imgur.com/ntC1q.png

 

참고URL

- netstat 명령어 : https://scbyun.com/395

- https://www.ictshore.com/free-ccna-course/transmission-control-protocol-advanced/

- https://totozhang.github.io/2016-01-23-tcp-connection-status-transit/TCPState2.png