https://learn.kalschatzi.com/module2/index.html Computer Networks Module Objectives This model will cover computer networks, how they are structured, their protocolos and some deep-dives into how the internet as a whole works. What we’ll cover: OSI Model TCP and UDP HyperText Transfer Protocol Networking Concepts What happens when I enter a URL on a browser? Traffic Routing Hugo en-us https://learn.kalschatzi.com/module2/1-osi-model/index.html Mon, 01 Jan 0001 00:00:00 +0000 https://learn.kalschatzi.com/module2/1-osi-model/index.html The OSI (Open Systems Interconnection) model is a conceptual framework used to understand how different networking protocols interact in a layered architecture. It standardizes network communication into seven layers, each responsible for a specific function. This model helps different systems communicate, ensuring interoperability between devices and software from different vendors. There are seven layers in the OSI model 1 - Physical Layer Deals with the physical transmission of data over a medium (cables, fiber optics, radio waves). Converts digital bits into electrical, optical, or radio signals. Includes hardware components like network cables, switches, and repeaters. 2 -Data Link Layer Ensures error-free transmission of data between two directly connected nodes. Divided into two sublayers: MAC (Media Access Control) – Controls access to the physical medium. LLC (Logical Link Control) – Manages frame synchronization and error checking. Examples: Ethernet, Wi-Fi, MAC addresses. https://learn.kalschatzi.com/module2/2-tcp-and-udp/index.html Mon, 01 Jan 0001 00:00:00 +0000 https://learn.kalschatzi.com/module2/2-tcp-and-udp/index.html There are two main protocols the internet is based on, TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) These are both layer 4 protocols. TCP - Transmission Control Protocol TCP is the most widely used protocol. A lot of other protocols are based on it, including HTTP. Key points: Connection-oriented – Establishes a connection before data transfer (via a three-way handshake: SYN (Synchronize) – Client sends a SYN packet to request a connection. SYN-ACK (Synchronize-Acknowledge) – Server responds with SYN-ACK to acknowledge the request. ACK (Acknowledge) – Client sends an ACK to confirm the connection is established. Reliable – Ensures all data is received in the correct order with retransmissions if packets are lost. Error checking – Uses checksums and acknowledgments to verify data integrity. Flow control – Adjusts data transmission speed based on network conditions. TCP is used when you need a reliable connectivity without any packet loss. https://learn.kalschatzi.com/module2/3-http/index.html Mon, 01 Jan 0001 00:00:00 +0000 https://learn.kalschatzi.com/module2/3-http/index.html HyperText Transfer Protocol (HTTP) is an application-layer protocol used for transferring hypertext (web pages, images, videos, etc.) between clients (browsers) and servers. It is stateless, meaning each request is independent and does not retain session information. This protocol is built on top of TCP Workflow Client Request: A web browser or app sends an HTTP request to a web server. Server Processing: The server processes the request, retrieves the requested resource, and generates a response. Server Response: The server sends an HTTP response, which includes the requested data and metadata (headers, status codes). Rendering: The client processes the response (e.g., a web browser renders an HTML page). HTTP Request Structure A request consists of: https://learn.kalschatzi.com/module2/4-networking-concepts/index.html Mon, 01 Jan 0001 00:00:00 +0000 https://learn.kalschatzi.com/module2/4-networking-concepts/index.html IP Addresses What is an IP? An IP address (Internet Protocol address) is a unique identifier for a device on a network. It’s like a street address for your computer. There are two types: IPv4 Most common. Format: xxx.xxx.xxx.xxx (e.g. 192.168.1.10) Each part is called an octet (range: 0 to 255) This uses 32-bit addresses. This means there are 2³² = 4,294,967,296(~4.3 billion) possible unique IPv4 addresses. Example: 192.168.1.1 Considering there are 8 billion people on earth, this number feels short. Which is why there is an IPv4 exhaustion. https://learn.kalschatzi.com/module2/5-i-visit-a-website/index.html Mon, 01 Jan 0001 00:00:00 +0000 https://learn.kalschatzi.com/module2/5-i-visit-a-website/index.html When you input a URL (Uniform Resource Locator) into a browser, a series of processes occur to retrieve the requested resource (like a webpage). Here are all the steps: 1 - User Enters URL You type a URL (e.g., https://learn.kalschatzi.com) into the browser’s address bar. 2 - DNS Resolution (Domain Name System) DNS Lookup: The browser first checks if the domain (e.g., learn.kalschatzi.com) is already cached from previous visits. If not, it queries a DNS server to resolve the domain name into an IP address (e.g., 192.0.2.1). https://learn.kalschatzi.com/module2/6-traffic-routing/index.html Mon, 01 Jan 0001 00:00:00 +0000 https://learn.kalschatzi.com/module2/6-traffic-routing/index.html Reverse Proxy This is server that is used as the entrypoint to your machine, using then the request Host and Path requested (layer 7) to route traffic to the appropriate machine. Let’s imagine you have multiple servers running in your LAN. You would expose your reverse proxy to the internet, that proxy would receive all request and the route then accordingly. For example kalschatzi.com routes to one internal IP and port, and learn.kalschtzi.com to another different pair of IP and port.