Firewall

A firewall is a control placed at the boundary between networks that permits or blocks traffic according to predefined rules — deciding who may talk to whom, on which ports and protocols.

Term

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A firewall is a control placed at the boundary between networks that permits or blocks traffic according to predefined rules — deciding who may talk to whom, on which ports and protocols.

Description

Traditional firewalls inspect source and destination address, port, and connection state. Next-generation firewalls (NGFW) add application awareness and user identity, so policy becomes "this application, for this user" rather than merely "port 443 allowed". Unlike a WAF, which protects a single web application, a network firewall sits at the boundary of an entire network or zone.

A firewall is not only a barrier at the entrance. Egress filtering is often more valuable: many intrusions surface only when a compromised host tries to reach its command-and-control server. If outbound traffic is left open "just in case", the firewall has done half its job.

What people often say

We have a firewall, so the network is secure.
A perimeter firewall is enough — internal traffic does not need filtering.

Covers / does not cover

Covers

Controlling permitted traffic between networks and zones
Blocking unauthorized access to externally exposed services
Restricting outbound (egress) traffic to unknown destinations
Application and user awareness of traffic (NGFW)

Does not cover

Attacks using permitted paths (e.g. phishing over allowed mail and web)
Threats within the same zone, where the firewall does not sit in the path
Encrypted traffic content when inspection is not performed

Mentioned in the news

Threats

reduces 8

Threats it reduces. Select one to open its page.

Techniques

neutralizes 7

Techniques it neutralizes. Select one to open its page.