D-Link DFL-700 [28/131] Firewall

Firewall

Policy

The Firewall Policy configuration section is the "heart" of the firewall. The policies are the

primary filter that is configured to allow or disallow certain types of network traffic through the

firewall. The policies also regulate how bandwidth management, traffic shaping, is applied to

traffic flowing through the WAN interface of the firewall.

When a new connection is being established through the firewall, the policies are

evaluated, top to bottom, until a policy that matches the new connection is found. The Action

of the rule is then carried out. If the action is Allow, the connection will be established and a

state representing the connection is added to the firewall's internal state table. If the action is

Drop, the new connection will be refused. The section below will explain the meanings of the

various action types available.

Policy modes

The first step in configuring security policies is to configure the mode for the firewall. The

firewall can run in NAT or No NAT (Route) mode. Select NAT mode to use DFL-1000 network

address translation to protect private networks from public networks. In NAT mode, you can

connect a private network to the internal interface, a DMZ network to the dmz interface, and a

public network, such as the Internet, to the external interface. Then you can create NAT mode

policies to accept or deny connections between these networks. NAT mode policies hide the

addresses of the internal and DMZ networks from users on the Internet. In No NAT (Route)

mode you can also create routed policies between interfaces. Route mode policies accept or

deny connections between networks without performing address translation. To use NAT

mode select Hide source addresses (many-to-one NAT) and to use No NAT (Route) mode

choose No NAT.

Action Types

Drop – Packets matching Drop rules will immediately be dropped. Such packets will be

logged if logging has been enabled in the Logging Settings page.

Reject – Reject works in basically the same way as Drop. In addition to this, the firewall

sends an ICMP UNREACHABLE message back to the sender or, if the rejected packet was a

TCP packet, a TCP RST message. Such packets will be logged if logging has been enabled

in the Logging Settings page.

Allow – Packets matching Allow rules are passed to the stateful inspection engine, which

will remember that a connection has been opened. Therefore, rules for return traffic will not be

required as traffic belonging to open connections is automatically dealt with before it reaches

the policies. Logging is carried out if audit logging has been enabled in the Logging Settings

page.