NetComm NB712 manual Firewall

2 Firewall

A firewall protects networked computers from an 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 two networks to see if it meets certain criteria. If it does, it is routed between the networks, otherwise it is stopped. A firewall filters both inbound and outbound traffic. It can also manage public access to private networked resources such as host applications. It can 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 source and destination addresses and port numbers. This is known as address filtering. Firewalls can also filter specific types of network traffic. This is known as protocol filtering because the decision to forward or reject traffic is dependant upon the protocol used, for example HTTP, ftp or telnet. Firewalls can also filter traffic by packet attribute or state.

It is important to note that an Internet firewall cannot prevent individual users with modems from dialling into or out of the network. By doing so they bypass the firewall altogether and open the network to attack. However, these are management issues that should be raised during the planning of any security policy and cannot be solved with Internet firewalls alone.

			Unknown Traffic
NB714 or NB712
G.SHDSL Modem Router	Access to Specific Destination		Specified Allowed Traffic
(Note: NB714 model shown)				Internet
	Allowed Traffic		Out to Internet
	Restricted Traffic	Firewall

PC PC PC PC

8	NB712 / NB714 User Guide
	YML829 Rev1