Consider the following network. ISP B provides national backbone service to regional ISP A. ISP C provides national backbone service to regional ISP D. Each ISP consists of one AS. B and C peer with each other in two places using BGP. Consider traffic going from A to D. B would prefer to hand that traffic over to C on the West Coast (so that C would have to absorb the cost of carrying the traffic cross-country), while C would prefer to get the traffic via its East Coast peering point with B (so that B would have carried the traffic across the country). a. What BGP mechanism B might use so that C would hand over D-to-A traffic at its West Coast peering point?

b. Given parts a and b, does the traffic from A-to-D and the traffic from D-to-A go through the same path (using the same gateway routers in each AS) in opposite directions? Explain.

c. How can B and C advertise routes such that the paths from A to D and D to A are the same but in opposite directions?