netstat

netstat displays network statistics — active connections, listening ports, routing tables, and interface statistics.

Common flags

netstat -natup

• -n — Show numerical addresses instead of resolving hostnames
• -a — Show all sockets (listening and established)
• -t — TCP connections only
• -u — UDP connections only
• -p — Show the process/PID associated with each socket

netstat -i

Shows a table of per-interface network statistics (packets sent/received, errors, drops).

Related

• tcpdump — capture and analyze live network traffic
• ss — modern replacement for netstat (part of iproute2)