ZyXEL 35 Guia Do Utilizador

 

 

All contents copyright (c) 2006 ZyXEL Communications Corporation.   

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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. 

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.   

1.  The ZyWALL's firewall inspects packets contents and IP headers. It is applicable to all protocols, 

that understands data in the packet is intended for other layers, from network layer up to the 

application layer.   

2.  The ZyWALL's firewall performs stateful inspection. It takes into account the state of connections 

it handles so that, for example, a legitimate incoming packet can be matched with the outbound 

request for that packet and allowed in. Conversely, an incoming packet masquerading as a 

response to a nonexistent outbound request can be blocked.   

3.  The ZyWALL's firewall uses session filtering, i.e., smart rules, that enhance the filtering process 

and control the network session rather than control individual packets in a session.   

4.  The ZyWALL's firewall is fast. It uses a hashing function to search the matched session cache 

instead of going through every individual rule for a packet.