Public IP vs. Private IP and Port Forwarding (Explained by Example)

Summary

This video explains the differences between public and private IP addresses and how to expose a local application to the internet. It covers the role of routers in assigning IPs, the concept of port forwarding, and how to configure a router to allow external access to a local application. The video also highlights security concerns when exposing internal networks. Using a basic Node.js application as an example, the presenter demonstrates how to set up port forwarding for public access while explaining potential risks and precautions.

Takeaways

• 🌐 Public IP vs Private IP: The video explains the difference between public and private IPs and why using a public IP doesn't always expose your application to the internet.
• 💻 Router's Role: The router is the device that gets the public IP address, while the rest of your devices receive private IPs on your local network (LAN).
• 🔑 Addressing in LAN: Devices in the LAN get internal IPs like 192.168.x.x, which are not accessible on the internet.
• ❌ Access Error: If someone tries to access your app using your private IP, they will get an error because private IPs aren't routable over the public internet.
• 🔁 Port Forwarding: To expose your local application to the public, you need to configure port forwarding on your router, linking a specific public port to your local machine's internal IP and port.
• ⚠️ Static IP Recommendation: It's recommended to use a static IP for your public IP, as dynamic IPs may change, causing your port forwarding setup to break.
• 🛡️ Security Risks: Exposing your local network to the public via port forwarding can be risky, so it's advised to only do this on non-critical machines.
• 👩‍💻 Demonstration: The video shows a practical example of setting up port forwarding to make a Node.js app publicly accessible.
• 📱 Mobile Test: The presenter demonstrates accessing the app from a mobile device using 4G (outside the local network) after configuring port forwarding.
• 🔧 Router Setup: The video explains how to configure port forwarding through the router's firewall options, specifying the internal device and port to forward traffic to.

Q & A

What common problem do developers face when moving an application from their local network to the public internet?

Developers often face issues where an application works fine on their local network using a private IP but fails to work when accessed from outside the local network, even when switching to a public IP.

Why can’t you use a private IP for external access to an application?

Private IPs, like '192.168.1.9', are only accessible within a local network and are not addressable on the public internet. External users will receive errors because private IPs are meant for internal use.

What is the role of a router in connecting local devices to the internet?

A router connects all devices on a local network to the internet by obtaining a public IP address. It assigns private IPs to local devices, enabling internal communication, but it blocks direct access from the outside unless configured otherwise.

What is port forwarding and how does it help in exposing local applications to the internet?

Port forwarding is a method where you instruct the router to forward requests from a specific public IP and port (e.g., 8080) to a specific private IP and port within your local network, making local applications accessible from the internet.

How do you configure port forwarding on a typical router?

You access the router’s settings, usually under the firewall or port forwarding section, and create a rule that maps an external port (e.g., 8080) to your machine’s private IP (e.g., 192.168.1.9) and port (e.g., 8080).

Why is it risky to expose your internal network through port forwarding?

Exposing your internal network can make it vulnerable to external attacks, as unauthorized users might gain access to your application or other sensitive data on your machine.

What is the importance of using a static public IP address for port forwarding?

A static public IP ensures that the external IP address does not change, allowing users to consistently access the application. If the IP changes frequently, you would need to update the port forwarding settings each time.

What alternative methods are available for exposing local applications to the internet besides port forwarding?

Other methods include using VPNs, reverse proxies, or services like Ngrok, which securely tunnel local applications to the public internet without modifying router settings.

Why might someone still face errors after using their public IP for external access?

Even after switching to a public IP, errors can occur if the router does not know how to forward traffic to the correct internal machine. This happens if port forwarding is not set up correctly.

What precaution should be taken if you decide to expose your application using port forwarding?

You should use port forwarding on a machine you don’t mind being exposed, apply security measures such as firewalls, and avoid exposing sensitive internal systems to reduce the risk of unauthorized access.