Upskilld

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.

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Network Proxies: The Different Types Explained

Network proxies are seen in many networks and used by enterprises, service providers and individuals. Three of the primary uses for proxies are forward proxies (seen in enterprise networks), reverse proxies (which deliver web services) and privacy/anonymisation focused proxies.