| 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. 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. In this way, the testing provided in these scenarios is deeper: The scenarios examine not only your knowledge, but also your understanding and ability to apply that knowledge to problems. If you do not get the correct answer, refer back to the previous chapters 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 19-1 Answers | 1: | Offer some reasons why the routing protocol EIGRP has recently been implemented in the network, and give the reasons for its deployment in that particular area of the network. | | A1: | EIGRP is being run across the Frame Relay WAN in areas using incremental updates, which is a more efficient use of resources. The network routers are all Cisco devices capable of running the proprietary protocol EIGRP. Using EIGRP is far more efficient on a WAN because incremental updates can be sent across the limited bandwidth. In particular, if either AppleTalk or IPX is running at the access level, the routing updates can be sent in EIGRP, which gives control and flexibility. EIGRP is used because it converges quickly, is classless, and is easy to deploy and maintain. | | 2: | The ISP has decided that the company should set a default route into its domain. Write out the commands that would configure the default route. | | A2: | The configuration commands to establish a default route from the company's network to the ISP domain are as follows: Router(config)# router eigrp 100 Router(config-router)# network 10.0.0.0 Router(config-router)# network 140.100.10.0 Router(config)# ip default-network 140.100.0.0 | | 3: | Is the router that is connecting to the ISP the only router that needs configuration? If this is the case, explain the reasons for your decision. If other routers need configuration, explain why they are needed and state where they would be applied. | | A3: | All the routers require a basic EIGRP configuration, but the router connecting to the ISP is the only router that needs additional configuration to connect to the ISP. Redistribution between the EIGRP processes occurs within the ISP. EIGRP automatically creates a default route, which will be propagated to all the other EIGRP routers automatically. The routers connecting to the RIP network need the EIGRP routes redistributed. Default routes redistributed into an RIP environment might require the ip classless command to be configured; this is for routers that are downstream from the router that is dealing with the redistribution. Because the routers at the redistribution points will have routes redistributed into them by EIGRP, they will have no problem in the lookup. | | 4: | The ISP router connecting into the company network will need static routes configured. Write out the commands to configure the router. | | A4: | The configuration commands to establish static routes from the ISP domain into the company's network are as follows: Router(config)# ip route 140.100.10.0 255.255.255.0 140.100.60.3 Router(config)# ip route 200.10.20.0 255.255.255.0 140.100.60.3 Router(config)# ip route 199.56.10.0 255.255.255.0 140.100.60.3 Router(config)# ip route 222.22.10.0 255.255.255.0 140.100.60.3 | | 5: | Will these routes need to be redistributed into the ISP domain? If the answer is yes, explain the reason for your decision, and then write out the configuration commands. If the answer is no, explain the reasons for your decision. | | A5: | The static commands defined in the previous answer need to be redistributed into the ISP domain. Static routes are not redistributed automatically. The passive-interface command prevents EIGRP updates from being sent to the customer. The commands for redistribution of static routes are as follows: Router(config)# router eigrp 100 Router(config)# redistribute static Router(config)# default-metric 10000 100 255 1 1500 Router(config)# passive-interface s0 | | 6: | Are filters required in this design? If so, state why, describe the type of filters required, and explain how and where they would be applied. | | A6: | Because there are no redundant paths in the redistribution between protocols, no filters are required in the configuration of the routers. There will be no feedback between the protocols. Because there is no routing protocol running between the company and the ISP, there is no requirement for filters here, either. If any filters were required, they would be for internal security and traffic control and would be typically configured on the access routers entering the Frame Relay cloud. There could also be some distribute lists at the distribution layer to limit connectivity among the different regions . | | 7: | A consultant has suggested that EIGRP should be configured using summarization. If this plan were to be implemented, on which routers would it be configured, and why? | | A7: | Summarization would be configured at the access level to limit the number of updates that need to traverse the WAN. |
Scenario 19-2 Answers Refer to Figure 19-2 to see the topology for this scenario. | 1: | Router A was chosen as the designated router on the LAN in the OSPF domain. Explain why this design choice was made, and give the command that would ensure its selection as the designated router. | | A1: | The router was selected by the administrator to be the designated router because it is an Autonomous System Boundary Router (ASBR). This makes it the most sensible choice. All traffic must pass through it to reach another domain. It should also be a more powerful router, because it must calculate redistribution and filtering and handle the role of designated router. The configuration to ensure that this router is chosen as the designated router is as follows: Router(config)# router ospf 100 Router(config)# interface Ethernet0 Router(config-if)# ip ospf priority 100 The designated router will have been selected manually by using this priority command or by configuring the router with the highest OSPF ID. This is achieved by allocating a loopback address. The default priority value is 1. If the value is set to 0, the router is ineligible to be a designated router (DR). | | 2: | Redistribution is occurring between IGRP and OSPF on Router A; state the configuration commands that you would use for both IGRP and OSPF. | | A2: | The configuration commands for redistributing OSPF into IGRP and IGRP back into OSPF follow: Router(config)# router igrp 100 Router(config-router)# passive-interface Ethernet0 Router(config-router)# network 201.100.10.0 Router(config-router)# redistribute ospf 100 metric 10000 100 255 1 1500 ! Router(config)# router ospf 100 Router(config-router)# passive-interface e1 Router(config-router)# network 144.250.0.0 0.0.255.255 area 0 Router(config-router)# redistribute igrp 100 metric 30 metric-type 1 subnets The use of the passive interface is unnecessary because the routing processes do not use the same Internet number. These commands will allow full connectivity between the two domains. The metric has been specified as 30. This is the seed metric that will be used on the routes entering OSPF from EIGRP. Because the routes are external, the route is made to appear farther away than the connected routes. The metric type is identified as type 1 external, meaning that the route will include the internal cost to the ASBR added to the external cost reported by the ASBR. | | 3: | The new headquarters of the merged company is in the OSPF domain. Therefore, because the connection to the Internet is also in this domain, it has been decided that Router A will have a default route configured to point to the OSPF domain from the IGRP domain. It will be necessary to configure the ip classless command for the IGRP domain. Explain why the ip classless command is needed and what it achieves. | | A3: | Normally, a classful routing protocol tries to match a destination address to a subnet it is attached to or to a remote classful network. Failing to find a match in either case causes the traffic to be dropped. Using the ip classless command amends this behavior so that unmatched traffic is also compared to less-specific routes (supernets or the default route) to try to find a match. | | 4: | Explain the use of the subnet command in OSPF, and why it is required in redistribution. | | A4: | The subnet command is used to propagate subnetworks into the OSPF domain instead of propagating the larger classful address. | | 5: | In a more complex topology with multiple redistribution points, explain why it might be necessary to filter when redistributing, and what it achieves in this network. | | A5: | The filter prevents feedback from OSPF into IGRP, and vice versa. In a network with more than one redistribution point, the networks can be redistributed at point A and then redistributed back into the domain that originated the route. Filtering out these routes avoids routing loops . |
Scenario 19-3 Answers | 1: | Create a transition plan, showing how the final design will be implemented. | | A1: | Figure 19-4 shows the answer to this question. Figure 19-4. Answer Diagram for Scenario 19-3, Question 1  In Figure 19-4, the transition would start at the core and move down to the distribution layer routers. The first move would be to place EIGRP in the Frame Relay cloud to alleviate the network overhead. After this is operational, the second phase would be to implement EIGRP in the FDDI ring because there are no end stations on the ring that require IPX RIP/SAP. | | 2: | If the transition plan requires redistribution, indicate these points on the diagram and provide the configuration commands. | | A2: | The configuration commands for Router G that provide for the redistribution between the different routing protocols are as follows: Router(config)# router rip Router(config-router)# network 10.0.0.0 Router(config-router)# passive-interface Ethernet 0 Router(config-router)# passive interface Token 0 Router(config-router)# redistribute eigrp 100 Router(config-router)# default-metric 3 Router(config)# router eigrp 100 Router(config-router)# network 140.100.0.0 Router(config-router)# passive-interface FDDI 0 Router(config-router)# redistribute rip Router(config-router)# default-metric 10000 100 255 1 1500 | | 3: | The company has also decided to connect to the Internet using EIGRP, upon which the ISP that is providing Internet connectivity has agreed. Is any redistribution required? Give reasons for your answers. | | A3: | If the ISP is in the same autonomous system as the company, no redistribution is required between the company and the ISP. Within the ISP domain, however, it is likely that the router connecting to the company in question is the only router that is a part of the autonomous system of the company. This is for security reasons. Therefore, some form of redistribution probably will be required in the ISP domain. | | 4: | Explain the neighbors that you see on the LAN segment and the path selection on Router B to network 140.100.0.0. | | A4: | The neighbors that are seen on the FDDI ring are the six routers that share the physical medium. Router B chooses the path as a successor because it provided the shortest path to the network stated, that is, a direct route through H. | | 5: | Create a diagram that shows the final network design, with configuration commands for EIGRP on Router A. | | A5: | Figure 19-5 shows the answer. Figure 19-5. Answer Diagram to Scenario 19-3, Question 5  In Figure 19-5, the command ip summary-address can be configured where appropriate at the distribution layer (the routers entering the Frame Relay cloud): Router A Router(config)# router EIGRP 100 Router(config-router)# network 140.100.0.0 Router(config-router)# ip summary-address eigrp 140.100.0.0 255.255.0.0 | | 6: | Write out the configuration commands for Router B. | | A6: | The configuration commands for Router B are as follows: Router(config)# router eigrp 100 Router(config-router)# network 140.100.0.0 Router(config-router)# no auto-summary Router(config-router)# ip summary-address 140.100.64.0 255.255.224.0 |
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