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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. |
TCP endpoints state transmission
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 |
performance diagram
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
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