network
2/+ connected devices (nodes) that can share resources
resources: data (file, image, msg), internet access
so computers can communicate and share information
How Digital Communication Works
- Everything is converted into binary (bits).
- Bits are 0s & 1s.
bits travel through:
- Electricity (copper cables)
- Light (fibre optic cables)
- Radio waves (Wi-Fi)
digital communication = sending 0s and 1s from one device to another.
What Is the Internet?
a global network of networks.
- Any device can join if it follows certain rules called protocols.
- protocol: set of communication rules.
Example: humans follow language rules to understand each other
2 Network Models (How Data Is Organised)
- TCP/IP Model (5 Layers)
- OSI Model (7 Layers)
models break communication into layers so we can understand each part separately.
PDNTA
TCP/IP 5-Layer Model (Very Important)
(delivery system)
Layer 1: Physical Layer
the hardware layer.
sends raw bits (0s and 1s) using:
Electrical signals
Light pulses
Radio waves
It does NOT understand data, just sends signals
Layer 2: Data Link Layer
- Groups bits into frames
- Adds sender and receiver MAC addresses
- Checks for errors using a checksum
A MAC address:
Is the physical address of your device
unique to each network card
used inside the same local network (LAN)
eg. house number inside a neighbourhood.
A Switch operates
It uses MAC addresses to send data to correct device.
Layer 3: Network Layer
uses IP addresses.
An IP address:
Identifies devices across diff networks
Allows communication across Internet
IP address has 2 parts
Network portion (which network you are on)
Host portion (which device you are)
A Router connects diff networks tgt
MAC address = house number
IP address = full street address (suburb + house number)
Layer 4: Transport Layer
Decides which application receives the data
Uses port numbers
Example:
Port 80 → Web browsing
Email uses different ports
2 main protocols:
TCP (reliable)
UDP (faster but less reliable)
Layer 5: Application Layer
what users see, allows applications to use network.
- HTTP (web browsing)
- HTTPS (secure browsing)
- SMTP (email)
OSI Model (7 Layers)
Extra layers:
Session Layer – manages conversations
Presentation Layer – formats and encrypts data
Types of Networks
LAN (Local Area Network)
- 1 physical location
- Example: Home Wi-Fi, UNSW building network
WAN (Wide Area Network)
- Connects multiple locations
- Example: Internet
3 network devices
HUB
Sends data to ALL devices
Causes collisions
Physical Layer device
SWITCH
Smarter than hub
Uses MAC addresses
Sends data only to correct device
Data Link Layer device
ROUTER
Connects different networks
Uses IP addresses
Network Layer device
3 Network Topologies (need?)
Topology = physical network layout.
Bus Topology
One backbone cable
If MAIN CABLE fails → entire network fails
Data collisions possible
Star Topology
All devices connect to central device
If CENTRAL SWITCH fails → network fails
Most common
Mesh Topology
Devices connected to each other
reliable & expensive
server vs hub
hub is unintelligent server and server is an intelligent hub
- Whensignals transmitted through server, able to be understood and transmitted,
- when signal (raw) sent to hub, unable to understand bits (info) given → unintelligent, doesnt go anywhere
- for signal to end need hub, (local network eg. your electronics only, simple)
If use WAN, internet, cloud –> use server
What Are Networking Protocols?
A network protocol is a set of rules that allows devices to communicate over a network.
just like humans need grammar and language rules to communicate clearly, computers need protocols to:
Format data
Send data
Receive data
Interpret data correctly
- operate at different layers (Transport, Application, etc.)
what ARP (Address Resolution Protocol) does
ARP finds the MAC address (physical address) of device when IP address known
Why this matters:
IP address = logical address
MAC address = physical hardware address
Devices need MAC addresses to COMMUNICATE inside a LOCAL network
ARP keeps a cache table mapping:
IP → MAC address
ARP Vulnerability: MITM Attack
An attacker can perform ARP poisoning:
1. Pretends to be the ROUTER
2. Redirects traffic to themselves
2 scenarios:
- Poisoning the client/server
Result:
Attacker INTERCEPTS/ MODIFIES DATA (Man-in-the-Middle attack)
Breaks CONFIDENTIALITY & INTEGRITY
DORA
what DHCP (Dynamic Host Configuration Protocol) does
automatically assigns IP addresses to devices
process:
DHCP DISCOVER (device broadcasts request)
DHCP OFFER (server offers IP)
DHCP REQUEST (device accepts)
DHCP ACK (server confirms)
This is how your laptop gets an IP when connect to WiFi.
DHCP Vulnerability (rogue DHCP server)
DHCP automatically assigns IP addresses to devices, clients typically accept DHCP responses without strong authentication.
- (MITM) Attacks
- can assign network settings that redirect traffic through a malicious system. may provide the attacker’s device as the default gateway.
- allows the attacker to intercept, monitor, or modify network traffic between the user and external networks.
- sensitive information such as login credentials or confidential data can be captured.
- Traffic Redirection and Phishing
an provide a fake DNS server address. When users attempt to access legitimate websites, the rogue DNS server can redirect them to malicious websites. phishing attacks where users unknowingly enter sensitive information on fraudulent pages.
- Denial of Service (DoS)
may provide incorrect /unusable network configurations. it might assign invalid IP addresses, incorrect subnet masks, or non-functional gateways. This can prevent devices from connecting to the network or accessing the internet, effectively causing a denial of service.
rogue DHCP server can:
An attacker may introduce fake DHCP server that:
Assigns incorrect IP settings
Provides attacker-controlled DNS
Routes traffic through attacker
Consequences:
Traffic interception
Phishing redirection
Network disruption
Loss of integrity and confidentiality
DHCP lacks authentication, making this possible
what (Network Address Translation) does
translates Private IP addresses → Public IP address
Example:
Your home network uses private IPs.
Your ROUTER translates them into one public IP to access internet.
NAT runs on routers.
- Saves IPv4 addresses
- Provides some privacy (internal IPs are hidden)
NAT (Network Address Translation) purpose
ranslates:
Private IP addresses → Public IP address
Private IP addresses are:
Not globally unique
Not routable on the internet
Public IP addresses:
Globally unique
NEEDED for internet communication
why NAT imp
Conserves IPv4 addresses.
Hides internal network structure.
Adds a basic layer of privacy.
NAT operates on routers connecting internal and external networks.
NAT security implications
converting info/data into a secret code using algorithms and keys to prevent unauthorized access
While NAT hides internal IP addresses, it is not true security.
It does not encrypt traffic or prevent sophisticated attacks.
Transport Layer Responsibilities
Segmentation of data
Reassembly of data
End-to-end communication
Ensuring delivery to correct application via port numbers
Reliability control (depending on protocol)
Two major protocols operate here: TCP and UDP.
TCP (Transmission Control Protocol)
Connection-oriented
Reliable
Ordered delivery
TCP 3-Way Handshake
SYN – Client requests connection.
SYN-ACK – Server acknowledges.
ACK – Client confirms.
then data transmitted.
Guarantees
No lost data (retransmission)
Correct order
No duplication
Error detection
TCP adds overhead but ensures reliability.
Used for:
Web browsing (HTTP/HTTPS)
Email
File transfers
UDP (User Datagram Protocol)
Connectionless
No handshake
No reliability guarantees
Sends data immediately
Does not confirm receipt
Does not ensure order
Used when speed is prioritised:
Video streaming
Gaming
VoIP
Trade-off:
Speed over reliability.
HTTP (Hypertext Transfer Protocol)
Transfers HTML documents between client and server
Uses:
TCP
Port 80
Process
User enters URL.
DNS resolves IP.
TCP connection established.
Client sends GET request.
Server returns HTML.
Browser renders page.
Security Issue
Unencrypted
Vulnerable to interception
Vulnerable to manipulation
HTTPS (HTTP over SSL/TLS)
HTTPS:
Uses TCP port 443
INFS1701_LecW2
Encrypts data
Authenticates server identity
SSL/TLS performs:
Handshake
Key exchange
Certificate verification
Indicated by:
https://
Padlock symbol
Prevents:
Eavesdropping
Data tampering
Man-in-the-middle attacks (when properly implemented)
