D-Link 800 - DFL 800 - Security Appliance, User Manual

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4.2. Static Routing
The most basic form of routing is known as Static Routing. The term static refers to the fact that
entries in the routing table are manually added and are therefore permanent (or static) by nature.
Due to this manual approach, static routing is most appropriate to use in smaller network
deployments where addresses are fairly fixed and where the amount of connected networks are
limited to a few. For larger networks however (or whenever the network topology is complex), the
work of manually maintaining static routing tables will be time-consuming and problematic. As a
consequence, dynamic routing should be used in those cases.
For more information about the dynamic routing capabilities of NetDefendOS, please see
Section 4.5, “Dynamic Routing”. Note however, that even if you choose to implement dynamic
routing for your network, you will still need to understand the principles of static routing and how it
is implemented in NetDefendOS.
4.2.1. The Principles of Routing
IP routing is the mechanism used in TCP/IP based networks for delivering IP packets from their
source to their ultimate destination through a number of intermediary network devices. These
devices are most often referred to as routers or firewalls.
In each router, one or more routing tables contain a list of routes and these are consulted to find out
where to send a packet so it can reach its destination. The components of a single route are
discussed next.
The Components of a Route
When a route is defined it consists of the following parameters:
• Interface
The interface to forward the packet on in order to reach the destination network. In other words,
the interface to which the destination IP range is connected, either directly or through a router.
The interface might be a physical interface of the firewall or it might be VPN tunnel (tunnels are
treated like physical interfaces by NetDefendOS).
• Network
This is the destination network IP address range which this route will reach. The route chosen
from a routing table is the one that has a destination IP range which includes the IP address
being sought. If there is more than one such matching route, the route chosen is the one which
has the smallest IP address range.
The destination network all-nets is usually always used in the route for public Internet access via
an ISP.
• Gateway
The IP address of the gateway which is the next router in the path to the destination network.
This is optional. If the destination network is connected directly to the interface, this is not
needed.
When a router lies between the D-Link Firewall and the destination network, a gateway IP must
be specified. For example, if the route is for public Internet access via an ISP then the public IP
address of the ISP's gateway router would be specified.
• Local IP address
This parameter usually doesn't need to be specified. If it is specified, NetDefendOS responds to
4.2. Static Routing Chapter 4. Routing
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