Policy Routing Using Linux®

Chapter 2. Policy Routing Theory

Traditional IPv4 routing is summarized as "All routing is a destination-driven process." When a router looks at an IPv4 packet it cares only about the destination address in the header of the packet. It uses this destination address to make a decision on where to forward the packet. This scenario works fine for simple networks where all of the machines in the network only need to get out to some place. Think of a standard driveway on a house. It starts at the house and goes to the road. When you get to the road you have two choices: turn right or turn left. The choice you make depends on where you want to go. Thus you make a destination-based routing choice. In the simplest case your driveway connects to a dead-end ...