What is Firewall?
A control that allows or blocks network traffic according to rules.
In plain English
A firewall sits between networks, or on a single device, and checks traffic against a rule set: which addresses, ports and protocols are permitted. Simple firewalls filter packets. Newer ones also track connections or inspect applications. Rules normally start by denying everything and then allowing only what is needed.
Example
A rule that allows inbound web traffic on port 443 to a web server and blocks everything else.
Easy to confuse with
- IDS and IPS: A firewall enforces allow and block rules. An IDS or IPS looks for signs of attack in traffic that the rules already allow.
Where you will meet it
This idea belongs to the subject area of these practice tests. We do not publish or predict real exam questions.
Related terms
- IDS and IPS: An IDS detects suspicious traffic and raises an alert. An IPS sits in the path and can block it.
- Zero trust: A security approach that never assumes a request is safe just because it comes from inside the network.
Quick answers
What is Firewall?
A control that allows or blocks network traffic according to rules.
What is the difference between Firewall and IDS and IPS?
A firewall enforces allow and block rules. An IDS or IPS looks for signs of attack in traffic that the rules already allow.
Test yourself
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