January 2015
Intermediate to advanced
432 pages
13h 23m
English
Content preview from Linux® Firewalls: Enhancing Security with nftables and Beyond, Fourth EditionBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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2. Packet-Filtering Concepts
What is a firewall? Over the years, the term has changed in meaning. According to RFC 2647, “Benchmarking Terminology for Firewall Performance,” a firewall is “a device or group of devices that enforces an access control policy between networks.” This definition is very broad, purposefully so in fact. A firewall can encompass many layers of the OSI model and may refer to a device that does packet filtering, performs packet inspection and filtering, implements a policy on an application at a higher layer, or does any of these and more.
A nonstateful, or stateless, firewall usually performs some packet filtering based solely on the IP layer (Layer 3) of the OSI model, though sometimes higher-layer protocols are involved ...
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