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How Linux Works
book

How Linux Works

by Brian Ward
May 2004
Beginner content levelBeginner
368 pages
8h 44m
English
No Starch Press
Content preview from How Linux Works

Firewalls

A firewall is a machine that sits between a network and the rest of the Internet, attempting to ensure that nothing "bad" from the Internet harms the network. You can also set up firewall features for each machine, where the machine screens all of its incoming and outgoing data at the packet level (as opposed to the application layer, where server programs usually try to perform some access control of their own). Firewalling on individual machines is sometimes called IP filtering.

To understand how firewalls work, consider that there are three times when a system can filter packets:

  • When the system receives a packet

  • When the system sends a packet

  • When the system forwards (routes) a packet to another host or gateway

With no firewalling in ...

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Publisher Resources

ISBN: 9781593270353Errata