Consider the network shown in Figure 4.29, in which horizontal lines represent transit providers and numbered vertical lines are interprovider links.

(a) How many routes to P could provider Q’s BGP speakers receive?

(b) Suppose Q and P adopt the policy that outbound traffic is routed to the closest link to the destination’s provider, thus minimizing their own cost. What paths will traffic from host A to host B and from host B to host A take?

(c) What could Q do to have the B−→A traffic use the closer link 1?

(d) What could Q do to have the B−→A traffic pass through R?

Figure 4.29)

A 1 Provider Q B 2 3 Provider P Provider R