Firewall

Firewall

A firewall is a security device or software that monitors, allows, or blocks network traffic based on predefined security rules.

Think of a firewall as a security guard at a building entrance:

Allowed traffic enters
Suspicious traffic is blocked
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Internet
|
Firewall
|
Internal Network
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What Does a Firewall Do?

A firewall can:

✅ Allow approved traffic

✅ Block unauthorized traffic

✅ Monitor connections

✅ Log network activity

✅ Protect against attacks

✅ Control access to resources

Network Firewall vs Host Firewall

These are the two major firewall types you'll see on the Network+ exam.

1. Network Firewall

A network firewall protects an entire network.

It sits between networks and filters traffic for many devices at once.

Example
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Internet
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Network Firewall
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PC Server Printer
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The firewall protects the entire company network.

Common Locations
Edge of a network
Between LAN and Internet
Between network segments
Examples
Cisco Firepower
Palo Alto Networks
Fortinet FortiGate
Check Point
SonicWall
Advantages of a Network Firewall

✅ Protects many devices

✅ Centralized management

✅ High performance

✅ Enterprise security features

Disadvantages

❌ Cannot fully protect devices from local threats already inside the network

❌ Single point of failure if not configured with redundancy

2. Host Firewall

A host firewall runs directly on an individual computer, server, or device.

Example
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Internet
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Laptop
|
Windows Firewall
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Each device has its own firewall.

Examples
Windows Defender Firewall
Linux iptables/nftables
macOS Firewall
Advantages of a Host Firewall

✅ Protects the individual device

✅ Works even outside the company network

✅ Can block application-specific traffic

✅ Protects against threats from the local network

Disadvantages

❌ Must be managed on each device

❌ Uses local system resources

Network Firewall vs Host Firewall
Feature	Network Firewall	Host FirewallProtects	Entire Network	One Device
Location	Network Edge	Installed on Computer
Management	Centralized	Per Device
Performance Impact	Firewall Appliance	Local Device
Example	Cisco Firepower	Windows Defender Firewall
Real-World Example
Network Firewall
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Internet
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Cisco Firewall
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Office Network
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The Cisco firewall filters traffic for everyone in the office.

Host Firewall
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Office Network
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Employee Laptop
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Windows Firewall
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The laptop's firewall protects that specific device.

Best Practice: Use Both

Most organizations use both network and host firewalls.

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Internet
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Network Firewall
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Corporate Network
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PC Server
| |
Host Host
Firewall Firewall
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This is called defense in depth because multiple security layers are protecting systems.

Common Firewall Types
Packet Filtering Firewall

Examines:

Source IP
Destination IP
Port numbers

Fast but basic.

Stateful Firewall

Tracks active connections and remembers session information.

Most modern firewalls are stateful.

Next-Generation Firewall (NGFW)

Provides:

Deep packet inspection
Malware detection
Application awareness
Intrusion prevention

Common in enterprises.

Network+ Exam Tips
Remember
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Hub = Layer 1
 
Switch = Layer 2
 
Router = Layer 3
 
Firewall = Security Device
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Key Difference

Network Firewall

Protects the entire network
Located between networks

Host Firewall

Protects a single device
Installed on the device itself
Quick Memory Trick
Plain Text
Network Firewall = Protects Everybody
 
Host Firewall = Protects Me
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Simple Definition

A firewall is a security device or software that controls network traffic based on security rules. A network firewall protects an entire network from external threats, while a host firewall runs on an individual computer or server and protects that specific device.

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