Description
This article is from the Firewalls
FAQ, by Matt Curtin cmcurtin@interhack.net and Marcus J. Ranum
mjr@nfr.com with numerous contributions by others.
17 What are the basic types of firewalls?
Conceptually, there are two types of firewalls:
1. Network layer
2. Application layer
They are not as different as you might think, and latest technologies are
blurring the distinction to the point where it's no longer clear if either
one is ``better'' or ``worse.'' As always, you need to be careful to pick
the type that meets your needs.
Which is which depends on what mechanisms the firewall uses to pass traffic
from one security zone to another. The International Standards Organization
(ISO) Open Systems Interconnect (OSI) model for networking defines seven
layers, where each layer provides services that ``higher-level'' layers
depend on. In order from the bottom, these layers are physical, data link,
network, transport, session, presentation, application.
The important thing to recognize is that the lower-level the forwarding
mechanism, the less examination the firewall can perform. Generally
speaking, lower-level firewalls are faster, but are easier to fool into
doing the wrong thing.
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security, Internet, firewalls, ssl, port, protection, application layer, proxy server, packet screening, filtering rules, viruses, terms
