Setting Up Loopback Interfaces With Routing Tables - D-Link NetDefendOS User Manual

Figure 3.9. Setting Up Loopback Interfaces with Routing Tables
A more detailed description of these steps is as follows:
1. Create a pair of loopback interfaces called LB1 and LB2, each has the other as its Loop to
parameter. Also define LB1 as a member of routing table RT1 and LB2 as a member of RT2.
2. Two configuration additions are now needed:
i. Define a route in RT1 that routes all-nets traffic (traffic to the Internet) to the loopback
interface LB1.
ii. Define an IP rule which allows Internet traffic to flow from LAN1 to LB1.
3. The Internet traffic that is sent through loopback interface LB1 will automatically arrives at
its partner LB2. Because LB2 is a member of the routing table RT2 that contains the all-nets
route, traffic can be successfully routed to the Internet.
However, two additions are still needed:
i. An IP rule needs to be defined which allows traffic to flow from LB2 to the Internet. This
could be in the same IP rule set as the previous rule and will probably be a NAT rule
which makes use of a single external IP address.
ii. A route needs to be defined which routes LAN1 traffic on the LB2 interface. This is
needed for traffic returning from the Internet.
The relationship of loopback interfaces with the routing tables and networks in this example is
illustrated below.
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Chapter 3: Fundamentals