# Networking Crash Course for the cloud Networking is the backbone of cloud computing. Whether you're deploying applications, managing virtual networks, or securing data, understanding core networking concepts is essential. In this crash course, we'll explore key networking topics as follows: * **OSI Model** * **TCP/IP Model** * **What is TCP?** * **What is UDP?** * **TCP vs UDP** * **DNS** * **SSH** * **IP Address and Subnetting** * **IP Classes** * **CIDR** ### **OSI Model** The **OSI (Open Systems Interconnection)** model provides a conceptual framework for understanding how data flows through a network. It has **7 layers**, each with specific responsibilities: ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1733323948043/c4a5774a-555e-4ac5-946d-5a7bc4287223.png align="center") 1. **Physical Layer** Manages the transmission of raw data bits over physical media (e.g., cables, Wi-Fi). *Example*: Ethernet cables. 2. **Data Link Layer** Ensures error-free data transfer between adjacent nodes. Includes MAC addresses. *Example*: Ethernet, Wi-Fi (802.11). 3. **Network Layer** Handles routing and addressing using IP addresses. *Example*: IPv4, IPv6. 4. **Transport Layer** Ensures reliable delivery (TCP) or faster, connectionless transfer (UDP). *Example*: TCP, UDP. 5. **Session Layer** Manages sessions and controls connections between applications. *Example*: Remote Desktop Protocol (RDP). 6. **Presentation Layer** Translates data formats for applications. Handles encryption and compression. *Example*: SSL/TLS encryption. 7. **Application Layer** Interfaces directly with users. *Example*: HTTP, FTP, DNS. ### **TCP/IP Model** The **TCP/IP model** - is essentially a condensed version of the OSI model widely used in modern networking. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1733324443958/9681d071-5f10-47e3-a62c-2e17637bbd99.png align="center") 1. **Link Layer** Combines the OSI Physical and Data Link layers. *Example*: Ethernet. 2. **Internet Layer** Maps to the OSI Network layer. Handles IP addressing and routing. *Example*: IPv4, IPv6. 3. **Transport Layer** Supports reliable (TCP) or best-effort (UDP) delivery of data. *Example*: TCP, UDP. 4. **Application Layer** Combines OSI Application, Presentation, and Session layers. *Example*: HTTP, FTP. ### **TCP vs. UDP** **What is TCP?** Transmission Control Protocol (TCP) is a communications standard that allows devices and applications to exchange data over a network. It's a fundamental protocol in the Internet Protocol (IP) suite and is a key part of the Internet's rules. TCP is responsible for ensuring that data is delivered **reliably** and in the correct order. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1733357992070/2670fe74-b57d-492e-9201-8fe39f22489e.png align="center") **TCP (Transmission Control Protocol)** * Ensures reliable data delivery through acknowledgment and retransmission. * Establishes a connection using a three-way handshake. * Suitable for applications needing accuracy (e.g., web browsing, file transfers). **What is UDP?** UDP stands for User Datagram Protocol, a communication protocol used to send data between computers on a network. UDP is often used for time-sensitive applications that require speed over reliability. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1733358174949/645add88-b525-42f8-a803-e7c4ec4c88da.png align="center") **UDP** * Focuses on speed and low latency. * Does not guarantee delivery, order, or error correction. * Ideal for real-time applications (e.g., video streaming, gaming). **Comparison Table** | **Feature** | **TCP** | **UDP** | | --- | --- | --- | | Reliability | Reliable | Unreliable | | Speed | Slower | Faster | | Use Cases | Web, file transfer | Streaming, gaming | ### **Domain Name System** **Domain Name System (DNS)** is the "phonebook" of the internet, translating human-friendly domain names like [`example.com`](http://example.com) into IP addresses `192.168.4.4` . This is required because nodes in a network need to know their “address” - in other words - IP - to reach and communicate. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1733957808307/3e6a7637-2060-46dd-ba74-2c403efb11a5.png align="center") * **Key Components**: * **DNS Servers**: Store mappings of domain names to IPs. * **DNS Records**: Types include: * **A Record**: Maps domain to IPv4. * **AAAA Record**: Maps domain to IPv6. * **CNAME**: Points to another domain. ### SSH Secure SHell is a network protocol that allows users to securely access and manage remote computers and systems over an unsecured network. It is commonly used in Linux environments. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1733958381846/51aca3d0-1c00-40aa-84ae-8ff2fb96b1d1.png align="center") ### **IP Addressing and Subnetting** ### **IP Addressing** An **IP address** is a unique identifier for devices on a network. It comes in two versions: * **IPv4**: 32-bit (e.g., `192.168.1.1`). * **IPv6**: 128-bit (e.g., `2001:0db8::1`). ### **Subnetting** **Subnetting** divides a network into smaller subnetworks, improving efficiency and security. * **Subnet Mask**: Determines the network and host portions of an IP. *Example*: * IP: `192.168.1.1` * Subnet Mask: `255.255.255.0` * Network: `192.168.1.0` * Hosts: `192.168.1.1` to `192.168.1.254` ### **IP Classes** IP addresses are divided into **classes** to categorize networks based on their size and usage. IP classes were part of the original design of IPv4 and are used to define ranges of IP addresses. Below are the key classes: **Class A** * **Range:** `1.0.0.0` to `126.255.255.255` * **Default Subnet Mask:** `255.0.0.0` (or `/8`) * **Purpose:** Very large networks, typically used by organizations with a huge number of devices. * **Addressing:** * The **first octet** represents the network. * The remaining three octets represent the host. Example: `10.0.0.1` Network: `10.0.0.0` Hosts: Over 16 million addresses. **Class B** * **Range:** `128.0.0.0` to `191.255.255.255` * **Default Subnet Mask:** `255.255.0.0` (or `/16`) * **Purpose:** Medium-sized networks, such as universities or large businesses. * **Addressing:** * The **first two octets** represent the network. * The last two octets represent the host. Example: `172.16.0.1` Network: `172.16.0.0` Hosts: About 65,000 addresses. **Class C** * **Range:** `192.0.0.0` to `223.255.255.255` * **Default Subnet Mask:** `255.255.255.0` (or `/24`) * **Purpose:** Small networks, such as small businesses. * **Addressing:** * The **first three octets** represent the network. * The last octet represents the host. Example: `192.168.1.1` Network: `192.168.1.0` Hosts: Up to 254 addresses. **Class D** * **Range:** `224.0.0.0` to `239.255.255.255` * **Purpose:** Reserved for **multicasting** (sending data to multiple hosts simultaneously). * **Addressing:** Does not use subnetting. **Class E** * **Range:** `240.0.0.0` to `255.255.255.255` * **Purpose:** Reserved for **experimental** purposes. Not used for general networking. **Special Ranges** 1. **Private IP Addresses:** * Reserved for internal use within a network. * Class A: `10.0.0.0` to `10.255.255.255` * Class B: `172.16.0.0` to `172.31.255.255` * Class C: `192.168.0.0` to `192.168.255.255` 2. **Loopback Address:** `127.0.0.0` to `127.255.255.255` (used for testing and diagnostics). 3. **APIPA:** `169.254.0.0` to `169.254.255.255` (used for automatic addressing when DHCP fails). **Classes are less relevant today because of the following reasons:** * **Classless Inter-Domain Routing (CIDR):** Modern IP address allocation uses CIDR, which allows flexible subnetting regardless of class. * **IPv6:** The introduction of IPv6 reduces reliance on IPv4 classes. ### **CIDR: Efficient IP Allocation** **CIDR (Classless Inter-Domain Routing)** simplifies IP allocation using a **prefix notation** (e.g., `/24`). * **Example**: `192.168.1.0/24` * `/24` means the first 24 bits define the network. * Host range: `192.168.1.1` to `192.168.1.254`. **Why It Matters in the Cloud** CIDR is widely used in defining **virtual private networks (VPNs)**, configuring **VPCs** in AWS, or **VNets** in Azure. This concludes our networking crash course for the cloud.