netstat

The netstat command is a monitoring tool that displays a wide range of network information.

Status information	Command
To find the status of the configured network interfaces	`netstat -in`
To check the routing information	`netstat -rn`
To observe a system's mbuf usage	`netstat -m`
To view the number of mbuf errors	`netstat -v`
To see statistics for all protocols configured on the system	`netstat -s`
To list the active sockets for your system	`netstat -a`
For only one protocol	`netstat -p <protocol>`
To show statistics for the IP protocol	`netstat -p ip`
To show statistics for the Internet Control Message Protocol	`netstat -icmp`
To show statistics for the TCP protocol	`netstat -p tcp`
To show statistics for the UDP protocol	`netstat -p udp`
To get information about packets sent and received, as well as sent and received and dropped	`netstat -D`
To get the state of all sockets	`netstat -an`
To get information about the network buffer cache	`netstat -c`