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. But what if you want to route packets differently depending not only on the destination addresses but also on other packet fields such as source address, IP protocol, transport protocol ports or even packet payload? This is Policy Routing and this book tells you how to do it.