Using Local Ip Address With An Unbound Network - D-Link NetDefend DFL-210 User Manual

4.2.1. The Principles of Routing
• Interface: The interface on which the second network is found.
• Network: The IP address range of the second network.
• Local IP Address: An address within the second network's IP range.
When the Default Gateway of the second network's clients is now set to the same value as the Local
IP Address of the above route, the clients will be able to communicate successfully with the
interface. The IP address chosen in the second network isn't significant, as long as it is the same
value for the Default Gateway of the clients and the Local IP Address.
The effect of adding the route with the Local IP Address is that the NetDefendOS will act as a
gateway with the Local IP Address and respond to, as well as send out, ARP queries as though the
interface had that IP address.
The diagram below illustrates a scenario where this feature could be used. The network 10.1.1.0/24
is bound to a physical interface that has an IP address within the network of 10.1.1.1. If we now
attach a second network 10.2.2.0/24 to the interface via the switch, it is unbound since the interface's
IP address doesn't belong to it.
Figure 4.2. Using Local IP Address with an Unbound Network
By adding a NetDefendOS route for this second network with the Local IP Address specified as
10.2.2.1, the interface will then respond to ARP requests from the 10.2.2.0/24 network. The clients
in this second network must also have their Default Gateway set to 10.2.2.1 in order to reach the
NetDefend Firewall.
This feature is normally used when an additional network is to be added to an interface but it is not
desirable to change the existing IP addresses of the network. From a security standpoint, doing this
can present significant risks since different networks will typically be joined together through a
switch which imposes no controls on traffic passing between those networks. Caution should
therefore be exercised before using this feature.
All Traffic Must have Two Associated Routes
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Chapter 4. Routing