🧑🏽‍💻 What REALLY Happens When You Type Localhost?

Summary

This video delves into the concept of 'localhost' and the loopback IP address (127.0.0.1), explaining how it works behind the scenes when you run a local server or test an application. It explores how the host file maps 'localhost' to this IP and why it’s essential for developers to test applications locally. The video also compares IPv4 (127.0.0.1) and IPv6 (::1) for localhost, touches on private vs. public IP addresses, and emphasizes localhost’s importance for secure, fast, and efficient testing and development, without requiring an internet connection.

Takeaways

• 😀 Local Host is a reserved domain name that always points back to your own machine, acting like a home address for your computer.
• 😀 When you type 'Local Host', your computer bypasses the DNS system and directly routes the request to itself using the loopback interface.
• 😀 The IP address 127.0.0.1 is commonly associated with Local Host, and it is hardcoded to reference the loopback interface.
• 😀 The loopback interface is a virtual network interface that sends data back to the same device, similar to throwing a tennis ball against a wall and having it bounce back.
• 😀 127.0.0.1 is the standard loopback address, but the entire 127.x.x.x range is reserved for loopback communication.
• 😀 Modifying the host file allows you to map custom names to the loopback IP, making it possible to use names like 'bem' instead of 'Local Host'.
• 😀 Local Host allows developers to test applications, APIs, and debug code locally without needing an internet connection.
• 😀 Local Host is also used for security purposes because requests to it never leave the machine, making it safe for testing sensitive applications.
• 😀 The loopback interface processes requests very quickly since there's no external routing, improving networking efficiency.
• 😀 Local Host can resolve to either IPv4 (127.0.0.1) or IPv6 (::1), depending on the system's network configuration, which JavaScript explicitly checks.
• 😀 IPv4 and IPv6 are both addressing systems for identifying devices on a network. IPv4 has limited address space, while IPv6 solves this with a much larger range of unique addresses.

Q & A

What is localhost and how does it work?

Localhost is a reserved domain name that always points back to your own machine, functioning like a home address for your computer. When you type 'localhost', your system routes the request directly to itself, skipping the DNS lookup process.

What is the significance of the IP address 127.0.0.1?

The IP address 127.0.0.1, often referred to as 'localhost', is a loopback address that always points back to your own device. It is used for network testing and internal communication on the same machine.

What is the loopback interface and how does it relate to localhost?

The loopback interface is a virtual network interface that sends data back to the same device. When you use 'localhost' or the IP address 127.0.0.1, your system processes the request internally without leaving the machine, thanks to this interface.

How does the operating system handle localhost requests?

When you type 'localhost', the operating system doesn’t query external DNS servers. Instead, it refers to the hosts file, where 'localhost' is mapped to 127.0.0.1, and then processes the request locally.

What happens if you modify the hosts file to map a custom name to 127.0.0.1?

If you modify the hosts file to map a custom name, such as 'bem', to 127.0.0.1, typing 'bem' in your browser or terminal will resolve the address to 127.0.0.1 and behave the same as 'localhost'.

What are the benefits of using localhost for developers?

Using localhost allows developers to test applications locally without needing an internet connection. It also provides security by ensuring requests stay on the local machine and offers fast processing through the loopback interface.

What is the difference between IPv4 and IPv6?

IPv4 is the traditional addressing system that supports around 4.3 billion unique addresses, while IPv6 was introduced to address the growing number of devices, offering 340 undecillion unique addresses, allowing every device to have its own unique address.

Why is localhost important for security testing?

Localhost provides a secure environment for testing sensitive applications because requests made to localhost never leave the machine, ensuring that no external network interference occurs.

How do Java, Python, and JavaScript handle localhost resolution?

Java and Python typically rely on the operating system's resolution mechanism to resolve localhost to 127.0.0.1. JavaScript, however, explicitly checks whether localhost resolves to IPv4 or IPv6, providing more control over the network behavior.

What is the difference between private IPs and localhost?

Private IPs are used within local networks and are not accessible from the internet. Localhost, on the other hand, is a special IP (127.x.x.x) reserved for internal communication on the same device, and it never leaves the machine.