TCP/IP

Ports in TCP and UDP

/etc/protocols and /etc/services

Shell commands:

• nc (netcat) is a shell command for «just about everything under the sun invovling TCP, UDP or UNIX-domain sockets».
• ss

Windows binaries ARP.EXE, PING.EXE, NETSTAT.EXE

web

The .NET class System.Net.Sockets.TcpClient

SSH provies secure network services over insecure networks (which TCP/IP networks typically are).

RFC 793