Network Security Fundamentals; Firewall and IDS; VPN — Virtual Private Network — Data Communication and Networking

Network Security Fundamentals

Common Network Attacks

Attack	Description
DoS (Denial of Service)	Overwhelm target with traffic to make it unavailable
DDoS	Distributed DoS — from many compromised machines
MITM (Man-in-the-Middle)	Attacker intercepts communication between two parties
Phishing	Trick users into revealing credentials via fake websites
ARP Spoofing	Send fake ARP replies to redirect traffic
DNS Spoofing	Redirect domain names to malicious IPs
SQL Injection	Insert malicious SQL into application inputs
Port Scanning	Discover open ports and services (Nmap)
Sniffer/Eavesdropping	Capture network traffic to read data
Ransomware	Encrypt victim's files and demand ransom

Security Measures

Measure	Description
Encryption	Encrypt data in transit (SSL/TLS, IPSec)
Firewall	Block unauthorized network traffic
IDS/IPS	Detect/prevent intrusions
VPN	Encrypted tunnel for remote access
Network segmentation	Isolate sensitive network segments
Access control	Authenticate and authorize users
Patch management	Keep systems updated
Monitoring	Log and analyze network traffic

Firewall and IDS

Firewall

A firewall filters network traffic based on rules to allow or block packets.

Types:

Type	Description
Packet Filter	Checks source/destination IP, port, protocol
Stateful Inspection	Tracks connection state; allows return traffic
Application Layer (WAF)	Inspects application-layer content
Next-Generation Firewall (NGFW)	Combines all above with deep packet inspection

Firewall Rules:

Rule 1: Allow TCP to port 80 (HTTP) from any source → PERMIT
Rule 2: Allow TCP to port 443 (HTTPS) from any source → PERMIT
Rule 3: Allow TCP from 192.168.1.0/24 to any → PERMIT (internal outbound)
Rule 4: Deny all other traffic → DROP (default deny)

IDS vs IPS

Feature	IDS	IPS
Full form	Intrusion Detection System	Intrusion Prevention System
Action	Detect and alert	Detect and block
Position	Passive (mirror port)	Inline
Response	Logs and notifies admin	Automatically blocks traffic

VPN — Virtual Private Network

What is VPN?

A VPN creates an encrypted tunnel over the internet to connect remote users or sites to a private network securely.

Remote Worker → [Encrypted VPN Tunnel] → [VPN Gateway] → Corporate Network
(Home/Hotel)         Internet                               (Private)

VPN Types

Type	Description	Use Case
Site-to-Site VPN	Permanent connection between two offices	Branch office connectivity
Remote Access VPN	Temporary connection for individual users	Work from home
SSL VPN	VPN via web browser (port 443)	Clientless access
IPSec VPN	IP Security protocol	Most enterprise VPNs

VPN Protocols

Protocol	Security	Speed	Notes
OpenVPN	High	Moderate	Open-source, widely trusted
WireGuard	High	Fast	Modern, efficient
IPSec/IKEv2	High	Fast	Standard enterprise protocol
L2TP/IPSec	High	Moderate	Common for mobile
PPTP	Low	Fast	Old, insecure — avoid

Network Security Fundamentals; Firewall and IDS; VPN — Virtual Private Network