ZyXEL Communications 2WG - Manual (Page 228)

ZyWALL 2WG Support Notes
All contents copyright (c) 2006 ZyXEL Communications Corporation.
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B01. What is a network firewall?
A firewall is a system or group of systems that enforces an access-control policy between two networks.
It may also be defined as a mechanism used to protect a trusted network from an un-trusted network. The
firewall can be thought of two mechanisms. One to block the traffic, and the other to permit traffic.
B02. What makes ZyWALL secure?
The ZyWALL is pre-configured to automatically detect and thwart Denial of Service (DoS) attacks such
as Ping of Death, SYN Flood, LAND attack, IP Spoofing, etc. It also uses stateful packet inspection to
determine if an inbound connection is allowed through the firewall to the private LAN. The ZyWALL
supports Network Address Translation (NAT), which translates the private local addresses to one or
multiple public addresses. This adds a level of security since the clients on the private LAN are invisible
to the Internet.
B03. What are the basic types of firewalls?
Conceptually, there are three types of firewalls:
1. Packet Filtering Firewall
2. Application-level Firewall
3. Stateful Inspection Firewall
Packet Filtering Firewalls generally make their decisions based on the header information in individual
packets. This header information includes the source, destination addresses and ports of the packets.
Application-level Firewalls generally are hosts running proxy servers, which permit no traffic directly
between networks, and which perform logging and auditing of traffic passing through them. A proxy
server is an application gateway or circuit-level gateway that runs on top of general operating system such
as UNIX or Windows NT. It hides valuable data by requiring users to communicate with secure systems
by mean of a proxy. A key drawback of this device is performance.
Stateful Inspection Firewalls restrict access by screening data packets against defined access rules. They
make access control decisions based on IP address and protocol. They also 'inspect' the session data to
assure the integrity of the connection and to adapt to dynamic protocols. The flexible nature of Stateful
Inspection firewalls generally provides the best speed and transparency, however, they may lack the
granular application level access control or caching that some proxies support.