Linux Commands | Network | netstat Check Network Status

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netstat Command

Short for network statistics, netstat is software or a tool that shows statistics for network interfaces or protocols. It is commonly used to measure network status and performance and to identify problems on the network.

netstat Usage

netstat [options] [| grep port-number or service-name]

Options:

  • -l (listen): Listening state
  • -n (number port): Port number
  • -t (tcp): TCP
  • -u (udp): UDP
  • -p (Program name / PID): Program name / PID. Shows which process is using the communication.
  • -a (all): All. Shows socket information for all states, not only ESTABLISHED.

netstat Usage Example

$ netstat
Active Internet connections
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)    
tcp4       0      0  192.168.0.1.62123      111.111.11.111.https   ESTABLISHED
  • Proto: Indicates the protocol used by the communication.
  • Recv-Q, Send-Q: Indicates the socket-size buffer used by the communication. Recv-Q means data that has not yet been processed through recv(), and Send-Q means the size of data sent through send() that has not yet been completely sent outside.
  • Local Address, Foreign Address: The local address and destination address used by the communication.
  • (state): Indicates a state such as ESTABLISHED or LISTEN.

NOTE

Port

A port is like an open door on a server and is represented by a number.
When connecting to a server by IP, the server may have multiple ports.

TCP and UDP

TCP: lower speed, bidirectional communication (higher reliability), request-response supported, stream
UDP: higher speed, one-way communication (lower reliability), no request-response, datagram (dgram)

Common netstat options

The netstat options are often used as -lntup.
Other combinations such as -antup, -ltup, and -atup are also used.

/etc/services

/etc/services is a file that defines service names and ports, and it can be used to check port numbers.