CyberSecurity & DevSecOps Expert: Develop, PenTest, and Deploy Secure Applications

**Theoretical Recap** A subnet (subnetwork) is a logical subdivision of an IP network. The core tool for defining subnets is CIDR (Classless Inter-Domain Routing) notation, written as an IP address followed by a prefix length (e.g., 192.168.1.0/24). ...

**Theoretical Recap** An IP address in IPv4 is a 32-bit number divided into two parts: the network portion and the host portion. CIDR notation (Classless Inter-Domain Routing) expresses this split using a suffix like /24 or /26, which indicates how m...

Understanding how IP addresses are organized and divided is a fundamental skill for anyone working in cybersecurity or network administration. You have already explored ports, transport protocols, and packet capture with tools like Wireshark and Nmap...

**Theoretical Recap** DNS (Domain Name System) is the protocol responsible for translating human-readable domain names (e.g., google.com) into IP addresses that machines can route. By default, DNS operates over UDP on port 53 — a deliberate design ch...

When you open Wireshark and start a capture on a busy network interface, you are immediately flooded with hundreds or even thousands of packets per second. Without a way to narrow down what you see, finding the traffic you care about becomes nearly i...

**Theoretical Recap** The TCP three-way handshake is the mechanism by which two hosts establish a reliable connection before any data is exchanged. It consists of three segments: SYN (client initiates, proposes an Initial Sequence Number), SYN-ACK (s...

Wireshark is one of the most widely used network protocol analyzers in the world. It allows you to capture and interactively browse the traffic running on a computer network. In the context of cybersecurity and DevSecOps, Wireshark is an essential to...

**Theoretical Recap** A port is a logical endpoint at the transport layer (Layer 4) that allows a host to run multiple network services simultaneously — this is the multiplexing concept you studied in the previous lesson. When you connect to a web se...

When a computer receives data over a network, it faces an immediate challenge: multiple applications are running simultaneously — a browser, an email client, a file transfer tool — and all of them may be receiving data at the same time. How does the ...

**Theoretical Recap** The TCP (Transmission Control Protocol) three-way handshake is the foundational mechanism by which two hosts establish a reliable connection before any data exchange occurs. It operates at Layer 4 (Transport) of the OSI model an...

Now that you have explored the first three layers of the OSI model — Physical, Data Link, and Network — you have seen how data travels as electrical signals, how Ethernet frames are built, and how routers forward packets across networks using IP addr...

## Project Overview In this mini-project, you will consolidate everything you have learned about OSI layers 1 through 3 by tracing, capturing, and documenting the complete journey of a network packet from your machine to a public website. This is not...

THEORETICAL RECAP Traceroute is a network diagnostic tool that maps the path packets take from your machine to a destination host, revealing each intermediate router (hop) along the way. It works by sending packets with incrementally increasing TTL (...

THEORETICAL RECAP Traceroute (or tracert on Windows) is a network diagnostic tool that maps the path packets take from your machine to a destination host, revealing each intermediate router — called a 'hop' — along the way. It operates at Layer 3 (Ne...

INTRODUCTION AND POSITIONING IN THE OSI MODEL You have already explored Layers 1 and 2 of the OSI model. You know that Layer 1 (Physical) handles signals and transmission media, and that Layer 2 (Data Link) manages the framing of data, error detectio...

THEORETICAL RECAP An Ethernet frame is a structured unit of data that operates at Layer 2 (Data Link) of the OSI model. It carries a payload from one MAC address to another within the same network segment. A standard Ethernet frame contains the follo...

THEORETICAL RECAP An Ethernet frame is the fundamental unit of data at Layer 2 (Data Link) of the OSI model. When two devices communicate on a local network, data is broken down into frames before being transmitted over the physical medium. Each Ethe...

Now that you have explored Layer 1, which deals with physical signals, cables, and transmission media, it is time to move up one level in the OSI model. Layer 2, called the Data Link layer, sits directly above the physical layer and adds the first la...

THEORETICAL RECAP At OSI Layer 1 (Physical), the cable is not just a wire — it is a medium that determines speed, distance, interference resistance, and ultimately, the reliability of your entire network stack. Three main cable families dominate ente...

You have already explored what the OSI model is, how encapsulation works, and what IP addresses and packets look like in practice. You even observed real network traffic with tools like ping and Wireshark. Now it is time to go deeper into the foundat...

**Theoretical Recap** The OSI model (Open Systems Interconnection) is a conceptual framework that standardizes network communication into 7 distinct layers: Physical (1), Data Link (2), Network (3), Transport (4), Session (5), Presentation (6), and A...

In the previous activities, you explored the basic vocabulary of networks, learned to identify IP addresses, observed packets with the ping command, and distinguished between switches and routers. You now have a solid mental picture of what a network...

**Theoretical Recap** Before diving into the simulator, let's consolidate what you've covered so far. A network is a set of interconnected devices (hosts) that exchange data through links in the form of packets. Each packet carries a source and desti...

Before diving into the differences between a switch and a router, it is essential to understand what a network topology is and why it matters for anyone working in cybersecurity or DevSecOps. A network topology describes the physical or logical arran...

**Theoretical Recap** An IP address (Internet Protocol address) is a unique numerical identifier assigned to every device connected to a network. IPv4 addresses are written in dotted-decimal notation (e.g., 192.168.1.1), composed of four octets rangi...