Scenario Answers

The answers provided in this section are not necessarily the only possible answers to the questions. The questions are designed to test your knowledge and to give practical exercise in certain key areas. This section is intended to test and exercise skills and concepts detailed in the body of this chapter.

If your answer is different, ask yourself whether it follows the tenets explained in the answers provided. Your answer is correct not if it matches the solution provided in the book, but rather if it has included the principles of design laid out in the chapter.

If you do not get the correct answer, refer back to the text and review the subject tested. Be certain to also review your notes on the question to ensure that you understand the principles of the subject.

Scenario 4-1 Answers

1.What needs to be done in addition to solve the problems caused by EIGRP? State the configuration commands necessary to activate this solution on Router A.
The WAN is a Frame Relay cloud, and Router A is the hub in the hub-and-spoke configuration. Each VC is 56 kbps.

In addition to readdressing the network, summarization would limit the query range of the routers. This would prevent the routes in the topology table being SIA, which seriously affects the performance of the network.

The commands required are as follows:

RouterA(config)# router eigrp 63
RouterA(config)# no auto-summary
RouterA(config)# network
RouterA(config)# int serial 0
RouterA(config-if)# ip summary-address eigrp 63
2.Give the commands to configure Router A for EIGRP over this NBMA cloud.
The configuration on Router A is as follows:
RouterA(config)# interface serial 0
RouterA(config-if)# frame-relay encapsulation
RouterA(config-if)# bandwidth 178

3.Give the commands to configure Router B for EIGRP over this NBMA cloud.
The configuration on Router B is as follows:
RouterB(config)# interface serial 0
RouterB(config-if)# frame-relay encapsulation
RouterB(config-if)# bandwidth 56

Scenario 4-2 Answers

1.How much bandwidth has each circuit been allocated? Why was this value chosen by the administrator?
Because a maximum of 256 kbps is available, you cannot allow any individual PVC to handle more than 25 kbps (256/10). Note that EIGRP will not use more than 22.5 kbps (90 percent of 25 kbps) on this interface, even though its capacity is 56 kbps. This configuration will not affect user data capacity, which will still be able to use the entire 56 kbps, except when EIGRP is using 22 kbps.
2.What bandwidth utilization is available to EIGRP? Why was this value chosen by the administrator?
Because this data rate is low, and because you do not expect very much user data traffic, you can allow EIGRP to use up to 90 percent of the bandwidth.
3.If Router A fails, what would the effect be on the network?
If Router A fails, there would be no communication between the routers in the WAN because Router A is the hub. Each site would function, but they would all be isolated from each other. The neighbor tables would fail to hear the hellos from the other routers connecting to the WAN and would time out all routes that they had heard from these routers. The topology table would be updated, and the routers would send updates to all their other neighbors.
4.Is summarization possible only on the routers entering the WAN cloud, or is it possible on the networks not shown in the figure, that are on the other side of the routers? Give reasons for your answers.
Summarization is possible on all interfaces in EIGRP, as long as the addressing scheme allows for it to be implemented. This is one of the major advantages of EIGRP over OSPF. OSPF can summarize only at ABRs.