In the example shown here, Site A has contracted with ISP 1 and Site B has contracted with ISP 2 for commodity Internet services. Because the GigaPOP's router will have a single best route for Destination C, traffic from both Site A and Site B will follow this best route (from ISP 1).

Without the ability to perform explicit routing--in other words, routing based on source and destination, rather than just destination--the GigaPOP cannot ensure that traffic intended for Destination C is following the path contracted by the traffic source.