Internet Protocols and Network Layers and Security

Physical Infrastructure: Previous lessons established the hardware base required for computers to communicate over a network. This infrastructure includes essential devices such as: * Servers. * Routers. * Switches.
Role of Protocols: While physical hardware provides the connection, protocols serve as the set of rules that dictate how these devices interact. Protocols are essential for the Internet's function as it scales.
Uniformity and Scaling: The Internet has grown to include more people and devices because of protocol uniformity. All components operate under the same assumptions, allowing the network to incorporate new devices over time without major service interruptions or structural changes.

Initial Transmission: Computers begin transmitting data to a larger network through technologies such as: * Ethernet. * Wireless Local Area Networks (LANs).
Introduction to IP: IP stands for Internet Protocol. It is the fundamental rule for how the Internet functions within the network layer.
IP Addressing: Every device connected to the Internet is assigned an IP address. This address acts as a unique identifier, analogous to a physical home address. This ensures: * Clear knowledge of where information is originating. * Precise destination for where information is being sent. * No confusion between destinations on the network.
Evolution of IP Versions: * Internet Protocol Version $4$ (IPv4): This version was used previously and supported a large number of devices, but eventually, the supply of addresses was exhausted by the growing number of connected devices. * Internet Protocol Version $6$ (IPv6): This is the upgraded version. It utilizes more bits and bytes to represent addresses, providing significantly more options than IPv $4$ to accommodate the expanding Internet.

The Transport Layer: Once the destination is known via the network layer, the transport layer determines how the information is sent. This layer is primarily composed of two protocols: TCP and UDP.
TCP (Transmission Control Protocol): TCP is described as a meticulous and organized protocol that prioritizes accuracy and complete data delivery. * Acknowledgments: TCP uses internal signals known as acknowledgments, which function similarly to "read receipts." * Mechanism: Every time a piece of data arrives at its destination, an acknowledgment is sent back. If the sender does not receive this acknowledgment, it assumes the data was lost and sends that specific package again. * Reliability: This ensures that the entire message, in all its constituent parts, arrives safely. * Drawback: The "double-checking" nature of TCP makes it slower than other methods.
UDP (User Datagram Protocol): UDP is described as a "fast and loose" protocol that prioritizes speed over absolute reliability. * Lack of Verification: UDP does not take the time to check if every piece of data has arrived at the destination. * Use Cases: It is frequently used for real-time applications where minor data loss is acceptable, such as: * Zoom calls. * YouTube videos. * User Interaction: In some cases, such as a dropped signal on a Zoom call, humans perform the role of TCP by manually asking others to repeat information if data bits were lost.

Definition: The application layer is the final layer of the Internet. It interprets information to help the computer understand what data represents and how to display it effectively to the user.
HTTP (Hypertext Transfer Protocol): This protocol dictates how computers send, receive, and display HTML code.
HTML (Hypertext Markup Language): This is the standard language used to create web pages. Every webpage viewed on a computer consists of HTML code delivered via the HTTP protocol.

Addressing Security Gaps: Standard Internet protocols and HTTP do not inherently ensure that information is transmitted in a private or secure manner.
HTTPS (Hypertext Transfer Protocol Secure): This provides an additional layer of security beyond regular HTTP. * Verification: It verifies that malicious code hasn't been injected into the HTML and ensures there are no hidden bugs in the web pages. * Indicators: Users can verify security by checking for "HTTPS" in the browser's address bar and looking for a lock icon next to the URL.
URL (Uniform Resource Locator): URLs like www.youtube.com provide a user-friendly way to navigate the Internet. * Abstraction from IP: URLs prevent users from having to memorize specific numerical IP addresses for every website. * Security Benefit: Because URLs are consistent and uniform, they help prevent users from accidentally visiting fake websites designed to steal information. * Stability: While physical street addresses stay the same, IP addresses for devices change every time a device reconnects to a network. The URL stabilizes this change, preventing network confusion.

Layer 1: Addressing: The Network Layer uses the Internet Protocol (IP) to assign unique IP addresses to every device.
Layer 2: Transmission: The Transport Layer uses TCP (reliable/slower) or UDP (fast/less reliable) to move data between devices.
Layer 3: Application: The Application Layer uses HTTP to transmit and present HTML code in a user-friendly format.
Security Layer: HTTPS and URLs provide safety and stable navigation across the network.