Free preview lesson from Network Security & Firewall Management.
Firewalls and intrusion detection only help if they are configured around a clear picture of what matters on the network and how it could be attacked. That picture is a threat model.
Four questions
- What assets matter? Servers, data stores, user devices, management interfaces.
- How does traffic flow? Sketch the main zones — internet, DMZ, internal, management — and the connections between them.
- What could go wrong? For each connection, consider spoofing, interception, unauthorized access and denial of service.
- What controls exist? Note the firewall rules, segmentation, encryption and monitoring already in place.
Default deny
A core principle is to block traffic by default and allow only what is needed. Every allowed rule should have a stated business reason and an owner.
Exercise
Draw a simple network diagram of a home or small-office network. Mark the zones, list the traffic that genuinely needs to cross between them, and write the minimum set of firewall rules to allow only that.
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