railaran: Cyber

1. What is Network Security?

Network security involves policies, practices, and technologies designed to protect the confidentiality, integrity, and availability of data and resources across networks.

Key Goals (CIA Triad):

Confidentiality: Only authorized users can access data.
Integrity: Data cannot be altered without authorization.
Availability: Data and services are accessible when needed.
👉Network Security refers to the policies, practices, and technologies used to protect networked systems, data, and resources from unauthorized access, misuse, modification, or disruption.

Its primary objective is to ensure the CIA Triad:
Confidentiality
Ensures that information is accessible only to authorized users.
Examples: encryption, access control, authentication.
Integrity
Ensures that data remains accurate and is not altered or tampered with without authorization.
Examples: hashing, digital signatures, checksums.
Availability
Ensures that network services and data are accessible to authorized users when needed.
Examples: redundancy, backups, DDoS protection, fault tolerance.

In short, network security protects data and systems by preventing unauthorized access, detecting attacks, and ensuring reliable network operation.

👍

Network security works by using multiple layers of protection to safeguard data and systems as they move across or reside within a network. These layers work together to prevent unauthorized access, detect threats, and ensure secure communication.

Access Control
Only authorized users and devices are allowed to access the network. This is achieved through authentication methods such as usernames, passwords, biometrics, and multi-factor authentication (MFA).
Goal: Only authorized users/devices can access the network.

Example: Using Linux PAM (Pluggable Authentication Module) for user authentication
# Add a new user
sudo adduser alice

# Require a strong password
sudo passwd alice
Example: Multi-Factor Authentication (MFA) with Google Authenticator
```
sudo apt install libpam-google-authenticator
google-authenticator
# Follow prompts to set up MFA for the user
```
For network devices: Use ACLs (Access Control Lists) to allow/block specific IPs:
```
access-list 100 permit ip 192.168.1.0 0.0.0.255 any
```
2. Firewalls

Goal: Filter traffic according to security rules.

Linux example using ufw:
```
# Enable UFW
sudo ufw enable

# Allow SSH
sudo ufw allow 22/tcp

# Deny all other incoming traffic by default
sudo ufw default deny incoming
```
Cisco example:
```
interface GigabitEthernet0/1
 ip access-group 100 in
```
3. Encryption

Goal: Protect data in transit.

Example: Using OpenSSL to create an encrypted file
```
openssl enc -aes-256-cbc -salt -in secret.txt -out secret.enc
openssl enc -d -aes-256-cbc -in secret.enc -out secret.txt
```
Example: Enabling HTTPS on a web server
```
sudo apt install certbot python3-certbot-apache
sudo certbot --apache
```
4. Intrusion Detection and Prevention (IDS/IPS)

Goal: Detect/block suspicious traffic.

Example: Installing Snort IDS
```
sudo apt install snort
sudo snort -c /etc/snort/snort.conf -i eth0
```
Snort can alert or drop malicious packets depending on the configuration.

5. Network Monitoring and Logging

Goal: Track network activity for anomalies.

Example: Using tcpdump to monitor traffic
```
sudo tcpdump -i eth0
```
Example: Using syslog for logging
```
sudo tail -f /var/log/syslog
```
6. Regular Updates and Patch Management

Goal: Fix vulnerabilities promptly.

Linux example:
```
# Update all packages
sudo apt update && sudo apt upgrade -y
```
Windows example (PowerShell):
```
Install-Module PSWindowsUpdate
Get-WindowsUpdate
Install-WindowsUpdate -AcceptAll -AutoReboot
```
7. Backup and Redundancy

Goal: Ensure data/service availability.

Linux example using rsync for backup
```
rsync -av --progress /home/user/ /backup/
```
Windows example using PowerShell
```
Copy-Item C:\Users\Alice\Documents D:\Backup\Documents -Recurse
```
Redundancy: For servers, use clustering or failover setups. Example with keepalived on Linux for high availability:
sudo apt install keepalived # Configure /etc/keepalived/keepalived.conf

1. Firewalls

Linux (UFW) example:

# Enable firewall
sudo ufw enable

# Allow SSH (port 22)
sudo ufw allow 22/tcp

# Deny all other incoming traffic
sudo ufw default deny incoming

Cisco example:

access-list 100 permit ip 192.168.1.0 0.0.0.255 any
interface GigabitEthernet0/1
 ip access-group 100 in

2. IDS/IPS

Snort installation & basic run (Linux):

sudo apt install snort
sudo snort -c /etc/snort/snort.conf -i eth0
# Snort will monitor traffic and log suspicious activity

Suricata example:

sudo apt install suricata
sudo suricata -c /etc/suricata/suricata.yaml -i eth0

3. Antivirus / Anti-malware

Linux ClamAV example:

sudo apt install clamav
sudo freshclam   # Update virus definitions
sudo clamscan -r /home/user  # Scan directory recursively

Windows Defender (PowerShell):

Start-MpScan -ScanType Full
Update-MpSignature

4. VPN

OpenVPN server setup example (Linux):

sudo apt install openvpn easy-rsa
make-cadir ~/openvpn-ca
cd ~/openvpn-ca
# Configure keys and certificates
sudo systemctl start openvpn@server

Client config example (client.ovpn):

client
dev tun
proto udp
remote your-vpn-server.com 1194
resolv-retry infinite
nobind
cipher AES-256-CBC
auth SHA256

5. Access Control

Linux user & group example:

# Add user
sudo adduser alice

# Add to group with limited access
sudo usermod -aG restrictedgroup alice

Windows Group Policy (PowerShell):

New-ADGroup -Name "VPNUsers" -GroupScope Global -Path "OU=Users,DC=example,DC=com"
Add-ADGroupMember -Identity "VPNUsers" -Members "Alice"

6. Encryption

Encrypt file with OpenSSL:

openssl enc -aes-256-cbc -salt -in secret.txt -out secret.enc
openssl enc -d -aes-256-cbc -in secret.enc -out secret.txt

HTTPS configuration (Apache example):

sudo apt install certbot python3-certbot-apache
sudo certbot --apache

7. Network Segmentation

VLAN example (Cisco):

vlan 10
 name HR
vlan 20
 name Finance
interface GigabitEthernet0/1
 switchport mode access
 switchport access vlan 10

8. Wireless Security

Linux hostapd example (Wi-Fi WPA2):

interface=wlan0
ssid=SecureWiFi
hw_mode=g
channel=6
wpa=2
wpa_passphrase=StrongPassword123

9. SIEM

Splunk forwarder installation (Linux):

wget -O splunkforwarder.tgz 'https://download.splunk.com/...'
tar -xvzf splunkforwarder.tgz -C /opt
/opt/splunkforwarder/bin/splunk start --accept-license
/opt/splunkforwarder/bin/splunk add forward-server splunk-server:9997

1. Malware & Ransomware

Mitigation: Use antivirus, scanning, and restricted permissions.

Linux ClamAV example:

sudo apt install clamav
sudo freshclam               # Update virus definitions
sudo clamscan -r /home/user  # Scan directory recursively

Windows Defender (PowerShell):

Start-MpScan -ScanType Full
Update-MpSignature

Extra tip: Limit executable permissions on sensitive directories to reduce ransomware impact.

2. Phishing Attacks

Mitigation: Train users, use email filtering, and enable multi-factor authentication (MFA).

Gmail example: Enabling spam filter and security alerts (via admin console, no code required).

Two-Factor Authentication (Linux PAM example):

sudo apt install libpam-google-authenticator
google-authenticator  # Follow prompts to enable MFA

Browser-based anti-phishing tips: Ensure HTTPS enforcement and anti-phishing extensions.

3. Denial-of-Service (DoS/DDoS)

Mitigation: Use firewalls, rate-limiting, and specialized DDoS protection.

Linux iptables example to limit connections:

# Limit SSH connections to 3 per minute per IP
sudo iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set
sudo iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --update --seconds 60 --hitcount 3 -j DROP

Cloudflare or AWS Shield can be configured to mitigate large-scale DDoS attacks.

4. Man-in-the-Middle (MITM)

Mitigation: Encrypt traffic and use secure network protocols.

HTTPS enforcement with Apache:

sudo a2enmod ssl
sudo a2ensite default-ssl.conf
sudo systemctl restart apache2

VPN configuration (OpenVPN) to secure communication:

sudo apt install openvpn easy-rsa
sudo systemctl start openvpn@server

ARP spoofing detection with arpwatch on Linux:

sudo apt install arpwatch
sudo arpwatch -i eth0

5. Unauthorized Access / Hacking

Mitigation: Strong passwords, access control, patching, and intrusion detection.

Linux example: Force password complexity

sudo apt install libpam-pwquality
sudo nano /etc/pam.d/common-password
# Add: password requisite pam_pwquality.so retry=3 minlen=12

Enable UFW firewall:

sudo ufw enable
sudo ufw allow 22/tcp
sudo ufw default deny incoming

Intrusion detection with Snort:

sudo apt install snort
sudo snort -c /etc/snort/snort.conf -i eth0

Extra tip: Regular patching is key:

sudo apt update && sudo apt upgrade -y

💡 Summary Table (Practical Mitigation)

Threat	Mitigation Tools/Config	Example Commands/Config
Malware/Ransomware	Antivirus, limited permissions	`clamav` scan, Windows Defender
Phishing	MFA, email filtering, user training	`libpam-google-authenticator`
DoS/DDoS	Firewalls, rate-limiting, cloud services	`iptables` rate limit
MITM	HTTPS, VPN, ARP monitoring	`a2enmod ssl`, OpenVPN, `arpwatch`
Unauthorized Access/Hacking	Firewalls, strong passwords, IDS	`ufw`, PAM password rules, Snort

1. Regular Software Updates and Patching

Goal: Fix vulnerabilities to prevent attacks.

Linux example:

# Update package list and upgrade all packages
sudo apt update && sudo apt upgrade -y

# For automatic security updates
sudo apt install unattended-upgrades
sudo dpkg-reconfigure --priority=low unattended-upgrades

Windows example (PowerShell):

# Install Windows updates
Install-Module PSWindowsUpdate
Get-WindowsUpdate
Install-WindowsUpdate -AcceptAll -AutoReboot

2. Strong Passwords & Multi-Factor Authentication (MFA)

Goal: Make unauthorized access difficult.

Linux: Enforce strong passwords

sudo apt install libpam-pwquality
sudo nano /etc/pam.d/common-password
# Add: password requisite pam_pwquality.so retry=3 minlen=12

Linux: Enable MFA using Google Authenticator

sudo apt install libpam-google-authenticator
google-authenticator  # Follow prompts to enable MFA for user accounts

Windows example: Enable MFA for Office 365 or AD users
Configured via the admin console; can also use PowerShell:

Connect-MsolService
Set-MsolUser -UserPrincipalName user@example.com -StrongAuthenticationRequirements @(@{RelyingParty="*";State="Enabled"})

3. Network Monitoring & Audits

Goal: Detect anomalies, intrusions, and security breaches.

Linux: Using tcpdump to monitor traffic

sudo tcpdump -i eth0

Linux: Using Snort IDS

sudo apt install snort
sudo snort -c /etc/snort/snort.conf -i eth0

SIEM Example: Splunk forwarder installation

wget -O splunkforwarder.tgz 'https://download.splunk.com/...'
tar -xvzf splunkforwarder.tgz -C /opt
/opt/splunkforwarder/bin/splunk start --accept-license
/opt/splunkforwarder/bin/splunk add forward-server splunk-server:9997

4. User Awareness Training

Goal: Reduce human errors like falling for phishing or downloading malware.

Implementation:

Conduct periodic security training sessions.
Simulate phishing emails (e.g., using tools like GoPhish).
Require users to follow strong password and data handling policies.

Example: Setting a login banner on Linux to remind users of security policy

sudo nano /etc/motd
# Add message: "Warning: Unauthorized access is prohibited. Follow security policies."

5. Defense-in-Depth (Layered Security)

Goal: Use multiple security layers so if one fails, others still protect the network.

Implementation examples:

Firewall rules (UFW):

sudo ufw default deny incoming
sudo ufw allow 22/tcp
sudo ufw allow 443/tcp
sudo ufw enable

IDS/IPS (Snort):

sudo apt install snort
sudo snort -c /etc/snort/snort.conf -i eth0

VPN (OpenVPN):

sudo apt install openvpn easy-rsa
sudo systemctl start openvpn@server

Encryption (HTTPS for web traffic):

sudo a2enmod ssl
sudo a2ensite default-ssl.conf
sudo systemctl restart apache2

User authentication (Strong passwords + MFA):

sudo apt install libpam-google-authenticator
google-authenticator

💡 Summary:

Best Practice	Example Implementation / Commands
Regular updates & patching	`sudo apt update && sudo apt upgrade -y` / PowerShell `Install-WindowsUpdate`
Strong passwords & MFA	PAM password policy + Google Authenticator / Windows AD MFA
Network monitoring & audits	`tcpdump`, Snort, Splunk forwarder
User awareness training	Security banners, phishing simulations
Defense-in-depth (layered)	Firewall + IDS + VPN + Encryption + MFA

1. Defense-in-Depth

The idea is multiple layers of protection so that if one layer fails, others still protect the network.

Perimeter Layer

Firewalls (UFW example on Linux)

sudo ufw default deny incoming
sudo ufw allow 22/tcp   # SSH
sudo ufw allow 443/tcp  # HTTPS
sudo ufw enable

IDS/IPS (Snort example)

sudo apt install snort
sudo snort -c /etc/snort/snort.conf -i eth0

VPN (OpenVPN)

sudo apt install openvpn easy-rsa
sudo systemctl start openvpn@server

Internal Network

Network Segmentation (VLAN example on Cisco)

vlan 10
 name HR
vlan 20
 name Finance
interface GigabitEthernet0/1
 switchport mode access
 switchport access vlan 10

Network Access Control (NAC)
- Example: Using FreeRADIUS for device authentication:

sudo apt install freeradius
sudo systemctl start freeradius

Devices must authenticate before accessing internal network.

Endpoint Layer

Antivirus

sudo apt install clamav
sudo freshclam
sudo clamscan -r /home/user

Patch Management

sudo apt update && sudo apt upgrade -y

Data Layer

Encryption

openssl enc -aes-256-cbc -salt -in secret.txt -out secret.enc

Backup

rsync -av /home/user/ /backup/

Monitoring Layer

SIEM (Splunk forwarder)

/opt/splunkforwarder/bin/splunk add forward-server splunk-server:9997

Threat Intelligence: Integrate feeds into SIEM or IDS.

2. Zero Trust Model

Principles:

“Never trust, always verify.”
Authenticate every device/user.
Apply least privilege access.
Use MFA and micro-segmentation.

Example Configurations:

MFA with Google Authenticator (Linux)

sudo apt install libpam-google-authenticator
google-authenticator

Micro-segmentation with VLANs

vlan 30
 name Sales
interface GigabitEthernet0/2
 switchport access vlan 30

Least privilege (Linux sudoers)

sudo visudo
# Allow only specific commands for user 'alice'
alice ALL=(ALL) /usr/bin/systemctl

3. Wireless Security

Best Practices with Configurations:

Use WPA3 and strong passwords

interface=wlan0
ssid=SecureWiFi
hw_mode=g
channel=6
wpa=3
wpa_passphrase=StrongPassword123

Separate guest and internal networks

# VLANs for guest network
vlan 100
 name GuestWiFi
interface wlan1
 switchport mode access
 switchport access vlan 100

MAC Filtering

# Allow only specific MAC addresses
macaddr_acl=1
accept_mac_file=/etc/hostapd/allowed_macs

Contents of allowed_macs:

00:11:22:33:44:55
66:77:88:99:AA:BB

💡 Summary Table

Strategy	Example / Configuration
Perimeter	UFW firewall, Snort IDS, OpenVPN
Internal Network	VLAN segmentation, FreeRADIUS NAC
Endpoint	ClamAV antivirus, patch updates
Data	OpenSSL encryption, rsync backup
Monitoring	Splunk forwarder, threat feeds
Zero Trust	MFA, least privilege, micro-segmentation
Wireless Security	WPA3, VLAN guest network, MAC filtering

6. Network Security Architecture

1. Perimeter Security

Goal: Protect the network edge and public-facing servers.

Firewall (UFW example on Linux)

sudo ufw default deny incoming
sudo ufw allow 22/tcp    # SSH
sudo ufw allow 80/tcp    # HTTP
sudo ufw allow 443/tcp   # HTTPS
sudo ufw enable

DMZ for Public Servers

Separate public servers (web/mail) from internal network using VLANs or a dedicated subnet.
Example Cisco VLAN for DMZ:

vlan 50
 name DMZ
interface GigabitEthernet0/3
 switchport mode access
 switchport access vlan 50

2. Network Core Security

Goal: Secure internal routers and switches.

Router/Switch ACLs

# Cisco example: deny external access to internal subnet
access-list 101 deny ip any 192.168.1.0 0.0.0.255
access-list 101 permit ip any any
interface GigabitEthernet0/1
 ip access-group 101 in

Network Segmentation

Separate departments using VLANs:

vlan 10
 name HR
vlan 20
 name Finance
interface GigabitEthernet0/2
 switchport mode access
 switchport access vlan 10

3. Endpoint Security

Goal: Protect devices from malware, unauthorized access, and data loss.

Antivirus / EDR

Linux (ClamAV):

sudo apt install clamav
sudo freshclam
sudo clamscan -r /home/user

Windows Defender / EDR:

Start-MpScan -ScanType Full
Update-MpSignature

Encryption

File encryption (Linux OpenSSL):

openssl enc -aes-256-cbc -salt -in secret.txt -out secret.enc

4. Data Security

Goal: Protect data both in transit and at rest.

Encryption in Transit (SSL/TLS)

Apache HTTPS example:

sudo a2enmod ssl
sudo a2ensite default-ssl.conf
sudo systemctl restart apache2

OpenSSL test of HTTPS certificate:

openssl s_client -connect example.com:443

Encryption at Rest (AES/RSA)

AES file encryption:

openssl enc -aes-256-cbc -salt -in data.txt -out data.enc

RSA encryption (public/private key):

openssl genrsa -out private.pem 2048
openssl rsa -in private.pem -outform PEM -pubout -out public.pem
openssl rsautl -encrypt -inkey public.pem -pubin -in secret.txt -out secret.enc

5. Monitoring & Response

Goal: Detect threats, log events, and respond to incidents.

SIEM (Splunk Forwarder)

wget -O splunkforwarder.tgz 'https://download.splunk.com/...'
tar -xvzf splunkforwarder.tgz -C /opt
/opt/splunkforwarder/bin/splunk start --accept-license
/opt/splunkforwarder/bin/splunk add forward-server splunk-server:9997

IDS/IPS (Snort example)

sudo apt install snort
sudo snort -c /etc/snort/snort.conf -i eth0

Incident Response

Maintain a documented plan including detection, containment, eradication, recovery, and lessons learned.
Example: Set up alerting via email when Snort detects malicious activity:

# In snort.conf, enable output to syslog or email alerts
output alert_syslog: LOG_AUTH LOG_ALERT