Lessons

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Access Control Lists for Beginners

Access control lists (ACLs) provide a simple but effective layer of security in modern networks.

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A Beginner's Guide to Binary

Binary is just another way of counting. Instead of using base-10 (decimal), we use base-2 where each place value is a bit.

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Basic Regex Character Matching

Learn how to match standard character classes with regular expressions.

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Block Ciphers

Block ciphers operate on blocks of data of a particular size.

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ARP: The Address Resolution Protocol

ARP helps us match IP addresses to hardware (MAC) addresses.

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CDP and LLDP

CDP and LLDP are similar layer two protocols for discovering information about neighboring devices.

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Collision and Broadcast Domains

Collision and broadcast domains are important properties of an Ethernet network.

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Custom Sets in Regular Expressions

Learn to define your own sets of characters to be matched with a regular expression.

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DNS: The Domain Name System

DNS is used to resolve friendly names (e.g. www.example.com) to IP addresses (e.g. 1.2.3.4), making it vital to our use of the internet.

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Ethernet at the Data-Link Layer

At the data-link layer, Ethernet provides an interface between the physical layer and the higher network layers. It also specifies MAC address formats.

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Firewalls in Computer Networking

Firewalls play an important part in protecting modern computer networks.

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Hashes and Computer Security

A cryptographic hash is a one way function for which it is very difficult to get back the input when given just the output.

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Ethernet at the Physical Layer

Ethernet sits at the link layer in TCP/IP but what does it define about the OSI physical layer?

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How does HTTP work?

HTTP is used by web browsers and many other applications to retrieve websites and much more.

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How to use the man pages on Linux

Getting help on Linux with the 'man pages' and where else to look.

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How does traceroute work?

The traceroute command is useful tool installed on hosts and network devices for troubleshooting networking issues by tracing the route of a packet across a network.

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Introduction to IPv4 Routing

IP routing is at the heart of the internet. It enables us to get packets from A to B across the globe.

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Linux directory commands for beginners

All the basics you need to learn for moving around the filesystem on the command line.

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Matching a Certain Number of Repetitions with Regex

Use regular expressions to match on a certain number (or range) of repetions of a certain character or class of characters.

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NAT: Network Address Translation

NAT is the mapping of one address to another. It is a useful tool for conserving IP address space.

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Netcat Field Guide

Netcat (nc) is a simple but versatile utility for TCP and UDP communication.

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Ping and ICMP

Ping is a useful tool for checking network connectivity using the Internet Control Message Protocol (ICMP).

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Regex Subexpressions

Subexpressions let us split a regular expression up into smaller groups which we can use for many things!

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Regex Anchors

We can specify where we want to match with a regular expression using word and string boundaries.

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RIP and RIPv2, The Routing Information Protocol

RIP was one of the first routing protocols to be implemented. RIPv2 later added a number of improvements.

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Routing Between VLANs

To let devices on one VLAN talk to the devices on another, we need to be able to route between them.

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How does IPv4 work?

IPv4 has been at the heart of the TCP/IP stack since it's inception. It is slowly being replaced by IPv6.

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Stream Ciphers

Stream ciphers are encryption algorithms which encrypt data one bit at a time.

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Summary of the TCP/IP Model

An overview of TCP/IP, or the Internet Protocol Suite, which underpins all modern computer networks.

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Same layer and adjacent layer interactions

Learn about interactions at the same layer and between adjacent layers, including encapsulation and protocol data units (PDUs).

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TCP: The Transmission Control Protocol

TCP is a connection-oriented protocol used at the transport layer to support protocols such as HTTP.

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The Complete Guide to IPv4 Subnetting

Learn how to design subnets and calculate the number of hosts on each.

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The Linux Terminal and Shell

Learn about the Linux terminal and why it's so useful.

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Telnet vs SSH

Telnet and SSH are both protocols used for interacting with remote devices. Learn about the differences and the details.

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The OSI 7 Layer Reference Model

A conceptual network model which is often used as a reference but not implemented practically.

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Types of Memory in Computer Architecture

There are different types of memory available for storing data in a computer. Learn about what they are and what they are used for.

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UDP: User Datagram Protocol

UDP is a simple transport layer protocol.

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Virtual LANs (VLANs)

VLANs are used in modern computer networks to support logically separate LANs on a single device.

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VLSM Subnetting in Networks

VLSM helps make more efficient use of available IP address space.

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WAN Technologies - HDLC, PPP, Frame Relay and Ethernet

Wide Area Networks may use one of several layer 2 technologies to encapsulate data as it cross a service providers network between a customer’s sites.

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What are Regular Expressions?

Regular expressions are patterns specified with a defined syntax which are used to search text for specific sequences of characters with many practical applications.

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What do network switches do?

Learn what network switches do in a TCP/IP network and how they work.

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What is a computer network?

An overview of what might constitute a computer network.

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What is a LAN?

Learn about devices found on local-area networks and how they are connected.

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What is a WAN?

Wide area networks enable data to be transferred across large geographic distances.

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Network Sockets and Ports

Network sockets are software structures that represent the endpoints of a network connection. A pair of sockets fully specify a network connection, and these connections enable communication in both directions. There are three main types of network socket: datagram, stream and raw.

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Using tcpdump: Options, Filters and Examples

'tcpdump' is a command-line tool available for UNIX based systems (including macOS and Linux) that captures network traffic and displays it on screen or saves it to a file. It is a simple but powerful tool for troubleshooting network problems, understanding protocols, investigating suspicious network activity, and much more.