CS 405: Cybersecurity

Module: Subnet Masks & Firewall Logic

Prof. Instructor

1. Concept Review: Understanding Masks

Firewalls use Masks to determine the "scope" of a rule. A mask defines how many bits of the IP address must match exactly.

Single Host (Scope: 1 Device)

IP: 192.168.1.10
Mask: 255.255.255.255 (/32)
Matches only this specific computer.

Entire Subnet (Scope: ~254 Devices)

IP: 192.168.1.0
Mask: 255.255.255.0 (/24)
Matches any device starting with 192.168.1.x

2. Activity: Traffic Simulation

Visualize how the firewall automatically handles "Established" traffic.

Waiting for traffic...

3. Lab: Manual Inspection with Masks

Define the source and destination details below. Note the new Mask fields, which determine if the rule applies to a specific host (/32) or a whole network (/24).

Connection State Table

Source IP Src Mask Dest IP Dst Mask Proto State Action
🔒 FIREWALL LOCKED