D-Link DFL-1660 User Manual page 242

4.7.1. Overview
forward the packet to the destination. If the route was a Switch Route, no specific information about
the destination is available and the firewall will have to discover where the destination is located in
the network.
Discovery is done by NetDefendOS sending out ARP as well as ICMP (ping) requests, acting as the
initiating sender of the original IP packet for the destination on the interfaces specified in the Switch
Route. If an ARP reply is received, NetDefendOS will update the CAM table and Layer 3 Cache
and forward the packet to the destination.
If the CAM table or the Layer 3 Cache is full, the tables are partially flushed automatically. Using
the discovery mechanism of sending ARP and ICMP requests, NetDefendOS will rediscover
destinations that may have been flushed.
Enabling Transparent Mode
The following steps are required to enable NetDefendOS Transparent Mode:
1. The interfaces that are to be transparent should be first collected together into a single Interface
Group object. Interfaces in the group should be marked as Security transport equivalent if
hosts are to move freely between them.
2. A Switch Route is now created in the appropriate routing table and the interface group
associated with it. Any existing non-switch routes for interfaces in the group should be
removed from the routing table.
For the Network parameter in the switch route, specify all-nets or alternatively, specify a
network or range of IP addresses that will be transparent between the interfaces (this latter
option is discussed further below).
3. Create the appropriate IP rules in the IP rule set to allow the desired traffic to flow between the
interfaces operating in Transparent Mode.
If no restriction at all is to be initially placed on traffic flowing in transparent mode, the
following single IP rule could be added but more restrictive IP rules are recommended.
Action
Allow
Restricting the Network Parameter
As NetDefendOS listens to ARP traffic, it continuously adds single host routes to the routing table
as it discovers on which interface IP addresses are located. As the name suggests, single hosts routes
give a route for a single IP address. The number of these routes can therefore become large as
connections are made to more and more hosts.
A key advantage of specifying a network or a range of IP addresses instead of all-nets for the
Network parameter is that the number of routes automatically generated by NetDefendOS will be
significantly smaller. A single host route will only be added if the IP address falls within the
network or address specified. Reducing the number of routes added will reduce the processing
overhead of route lookups.
Specifying a network or address range is, of course, only possible if the administrator has some
knowledge of the network topology and often this may not be the case.
Multiple Switch Routes are Connected Together
The setup steps listed above describe placing all the interfaces into a single interface group object
which is associated with a single switch route.
Src Interface Src Network
any all-nets
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Dest Interface Dest Network
any all-nets
Chapter 4. Routing
Service
all_services