Planet Technology G.SHDSL.bis Bridge Router GRT-504 - Manual (Page 16)

GRT-504 4-Wire G.SHDSL.bis Firewall Router User’s Manual
3 Getting to know Firewall feature
3.1 Introduction
A firewall protects networked computers from intentional hostile intrusion that could compromise
confidentiality or result in data corruption or denial of service. It must have at least two network
interfaces, one for the network it is intended to protect, and one for the network it is exposed to. A
firewall sits at the junction point or gateway between the two networks, usually a private network
and a public network such as the Internet.
A firewall examines all traffic routed between the networks. The traffic is routed between the
networks if it meets certain criteria; otherwise, it is filtered. A firewall filters both inbound and
outbound traffic. Except managing the public access to private networked resources such as host
applications, the firewall is capable of log all attempts to enter the private network and trigger
alarms when hostile or unauthorized entry is attempted. Firewalls can filter packets based on their
IP addresses of source and destination. This is known as address filtering. Firewalls can also filter
specific types of network traffic by port numbers, which is also known as protocol filtering because
the decision of traffic forwarding is dependant upon the protocol used, for example HTTP, ftp or
telnet. Firewalls can also filter traffic by packet attribute or state.
An Internet firewall cannot prevent the damage from the individual users with router dialing into or
out of the network, which bypass the firewall altogether. The misconduct or carelessness of
employee is not in the control of firewalls either. Authentication Policies, which is involved in the
use and misuse of passwords and user accounts, must be strictly enforced. The above
management issues need to be settled during the planning of security policy, but cannot be solved
with Internet firewalls alone.
Internet
Internet
Local User Internet
Allowed Traffic Out to Internet
Specified Allowed Traffic
Access to Specific
Destination
Restricted Traffic
Unknown Traffic
Firewall
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