D-Link DFL-1660 User Manual page 189

4.3. Policy-based Routing
the core interface (which are routes to NetDefendOS itself).
4. Click OK
Routing Rules can use IPv4 or IPv6 Addresses
Routing rules support either IPv4 or IPv6 addresses as the source and destination network for a
rule's filtering properties.
However both the source and destination network must be either IPv4 or IPv6. It is not permissible
to combine IPv4 and IPv6 addresses in a single rule. For further discussion of this topic, see
Section 3.2, "IPv6 Support".
The Forward and Return Routing Table can be Different
In most cases, the routing table for forward and return traffic will be the same. In some cases it can
be advantagous to have different values.
Take the example of a firewall with two hypothetical interfaces wan1 and wan2 connected to two
ISPs plus a protected network lannet on the lan interface. There are two routing tables, the main
routing table and an isp2 routing table which look like the following:
The main routing table
Index #
1
2
The isp2 routing table
Index #
1
If traffic coming through wan2 is to have access to lannet then a routing rule needs to constructed as
follows:
Source
Interface
wan2
This rule allows the forward traffic through the wan2 table to find the route for lannet in the main
routing table. The return traffic will use the isp2 table so it can reach the initiator of the connection.
This example should also have some address transation rules since lannet will probably be a private
IP network. For simplicity, that has been omitted.
The Routing Table Selection Process
When a packet corresponding to a new connection first arrives, the processing steps are as follows
to determine which routing table is chosen:
1. The routing rules are first looked up but to do this the packet's destination interface must be
determined and this is always done by a lookup in the main routing table. It is therefore
important that a match for the destination network is found or at least a default all-nets route
Interface
lan
wan1
Interface
wan2
Source Destination
Network Interface
all-nets any
189
Network
lannet
all_nets
Destination
all_nets
Destination Forward
Network Routing Table
lannet main
Chapter 4. Routing
Gateway
isp1_ip
Gateway
isp2_ip
Return
Routing Table
isp2