How To Use netstat

Introduction

netstat (network statistics) is a command line tool for monitoring network connections both incoming and outgoing as well as viewing routing tables, interface statistics etc. netstat is available on all Unix-like Operating Systems and also available on Windows OS as well. It is very useful in terms of network troubleshooting and performance measurement. netstat is one of the most basic network service debugging tools, telling you what ports are open and whether any programs are listening on ports.

Listing all the LISTENING Ports of TCP and UDP connections

$ netstat -a | more

Listing TCP Ports connections

Listing only TCP (Transmission Control Protocol) port connections:

$ netstat -at

Listing UDP Ports connections

Listing only UDP ( User Datagram Protocol ) port connections:

$ netstat -au

Listing All LISTENING Connections

Listing all active listening ports connections:

$ netstat -l

Listing All TCP Listening Ports

Listing all active listening TCP ports:

$ netstat -lt

Listing All UDP Listening Ports

Listing all active listening UDP ports:

$ netstat -lu

Listing all UNIX Listening Ports

Listing all active UNIX listening ports:

$ netstat -lx

Showing Statistics by Protocol

Displays statistics by protocol. By default, statistics are shown for the TCP, UDP, ICMP, and IP protocols. The -s parameter can be used to specify a set of protocols:

$ netstat -s

Showing Statistics by TCP Protocol

Showing statistics of only TCP protocol:

$ netstat -st

Showing Statistics by UDP Protocol

Showing statistics of only UDP protocol:

$ netstat -su

Displaying Service name with PID

Displaying service name with their “PID/Program Name”:

$ netstat -tp

Displaying Promiscuous Mode

Displaying Promiscuous mode with -ac switch, netstat print the selected information or refresh screen every five second. Default screen refresh in every second.

$ netstat -ac 5 | grep tcp

Displaying Kernel IP routing

Display Kernel IP routing table with netstat and route command:

$ netstat -r

Showing Network Interface Transactions

Showing network interface packet transactions including both transferring and receiving packets with MTU size:

$ netstat -i

Showing Kernel Interface Table

Showing Kernel interface table, similar to ifconfig command:

$ netstat -ie

Displaying IPv4 and IPv6 Information

Displays multicast group membership information for both IPv4 and IPv6:

$ netstat -g

Print netstat Information Continuously

To get netstat information every few second, then use the following command, it will print netstat information continuously, say every few seconds

$ netstat -c