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15.04.2022
Netstat is a console command that can provide detailed information about network connections, routing table, interface statistics, and similar network connection information.
The
netstat command is used with various parameters. These parameters and their meanings are as follows:
-a : Prints all TCP and UDP connections to the screen. -e : Displays statistics of incoming and outgoing packet counts. -n : Displays all connections
numerically. -o : Lists all connections by PID number and application name. -p : Prints the application and PID numbers used by connections to the screen. -s : Prints statistical data according to rules to the screen. -r : Displays the contents of the IP routing
table.
Meanings of Connection States in Netstat Output
ESTABLISHED : The socket connection has been established. SYN_SENT : The socket is trying to establish a connection. SYN_RECV : A connection request has arrived from the network. FIN_WAIT1 : The
socket has been closed, the connection is about to be terminated. FIN_WAIT2 : The connection has been terminated. The socket is waiting for the other end to terminate the connection. TIME_WAIT : The socket is waiting to receive packets that may arrive after it closes.
CLOSED : The socket is not in use. CLOSE_WAIT : The other end has closed the connection. The socket is waiting to close. LAST_ACK : The other end has terminated the connection and closed the socket. Waiting for confirmation. LISTEN : The socket is in listening mode
for incoming connections. CLOSING : Local and remote sockets have been closed but have not sent all their data. Sockets do not close until all data has been sent.
Some Example Commands to Get Netstat Output via SSH
Lists All TCP and UDP
Connections
netstat -ntu
Prints SYN_SENT and SYN_RECV connection states among all TCP and UDP connections to the screen. You can change the part after grep to your preference and see other connections on the screen.
netstat -ntu | grep
SYN
Prints only ESTABLISHED connections to the screen.
netstat -ntu | grep ESTABLISHED
The following command sorts the entire IP list including values printed with the ffff table from smallest to largest. You can also add grep to the command to list
by connection state.
netstat -ntu | awk ‘ {print $5} ’ | awk ‘ {sub(“::ffff:”,“”);print} ’ | cut -f1 -d ‘:’ | sort | uniq -c | sort -n | grep -v -e server -e Address 127.0.0.1 -e 0.0.0.0
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