TCP (Transmission Control Protocol) is a fundamental protocol for network communication, ensuring reliable data transmission between devices. For Apple users, particularly those using macOS, understanding how to establish and manage TCP connections can be crucial for tasks such as network troubleshooting, software development, and system administration. This article will guide you through the process of working with TCP connections on macOS, leveraging built-in tools and commands.

Examples:

1. Checking Active TCP Connections:

On macOS, you can use the netstat command to display active TCP connections. Open Terminal and run the following command:

   netstat -an | grep tcp

This command lists all active TCP connections, showing details such as local and remote addresses and the connection state.

2. Establishing a TCP Connection Using Telnet:

Although telnet is deprecated on macOS, you can still install it using Homebrew. First, install Homebrew if you haven't already:

   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Then, install telnet:

   brew install telnet

Now, you can establish a TCP connection to a server (e.g., example.com on port 80) using:

   telnet example.com 80

3. Using nc (Netcat) for TCP Connections:

Netcat (nc) is a versatile command-line tool available on macOS for managing TCP connections. To connect to a server:

   nc example.com 80

You can also use nc to listen for incoming TCP connections on a specific port:

   nc -l 1234

4. Monitoring Network Traffic with tcpdump:

tcpdump is a powerful packet analyzer tool available on macOS. To capture TCP traffic on a specific interface (e.g., en0):

   sudo tcpdump -i en0 tcp

This command captures and displays TCP packets in real-time.