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.

In this way, the testing provided in these scenarios is deeper: It examines 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 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 7-1 Answers

1:	Design the addressing scheme for the site so that summarization can be implemented at a later stage.
A1:	An addressing scheme for the Los Angeles site could be as shown in Figure 7-3. Figure 7-3. Scenario 7-1 Answer
2:	Determine the configuration that will be implemented across the Frame Relay cloud.
A2:	The Frame Relay configuration is a hub-and-spoke topology. Because Los Angeles is the central hub of the company, it is logical that it is also the network hub. The configuration in Frame Relay would therefore be a point-to-multipoint one. This avoids the DR/BDR election process, because it treats all the PVC links as a collection of point-to-point links, forming adjacencies across each link even though they are not separate point-to-point subinterfaces. Having separate links removes the need for the DR/BDR. This is a good solution if three different companies have a multivendor environment, because it conforms to the RFC standards. Example 7-13 shows a configuration that could be implemented. Example 7-13. Answer to Scenario 7-1 Configuration Question 2 Los Angeles interface serial 0 encapsulation frame-relay ip address 10.255.0.35 255.255.255.248 ip ospf network point-to-multipoint router ospf 100 network 10.0.0.0 0.255.255.255 area 0 San Francisco interface serial 0 encapsulation frame-relay ip address 10.255.0.36 255.255.255.248 ip ospf network point-to-multipoint router ospf 100 network 10.0.0.0 0.255.255.255 area 0 London interface serial 0 encapsulation frame-relay ip address 10.255.0.37 255.255.255.248 ip ospf network point-to-multipoint router ospf 100 network 10.0.0.0 0.255.255.255 area 0 If individual point-to-point networks are chosen , then a separate PVC and IP subnet will be required for the configuration. This is illustrated in Example 7-14. Example 7-14. Answer to Scenario 7-1 Configuration Question 2 Los Angeles interface serial 0 no IP address encapsulation frame-relay interface serial0.1 point-to-point ip address 10.255.0.35 255.255.255.252 frame-relay interface-dlci 21 interface serial0.1 point-to-point ip address 10.255.0.49 255.255.255.252 frame-relay interface-dlci 28 router ospf 100 network 10.0.0.0 0.255.255.255 area 0 San Francisco interface serial 0 no IP address encapsulation frame-relay interface serial0.1 point-to-point ip address 10.255.0.36 255.255.255.252 frame-relay interface-dlci 44 router ospf 100 network 10.0.0.0 0.255.255.255 area 0 London interface serial 0 no IP address encapsulation frame-relay interface serial0.1 point-to-point ip address 10.255.0.50 255.255.255.252 frame-relay interface-dlci 66 router ospf 100 network 10.0.0.0 0.255.255.255 area 0 Note that the Frame Relay cloud is a continuation of Area 0. This is a logical first step; it is advisable to change this configuration when OSPF is being run throughout the organization. When the other sites are up and running OSPF, the Los Angeles site could become another area. This would allow the summarization of routes across the Frame Relay cloud, which would reduce the traffic, cost, and possibility for congestion.
3:	State the configuration commands required to implement OSPF on the routers. Note that all the routers are to be in Area 0.
A3:	The configuration on the Los Angeles routers, not including the Frame Relay configuration, is shown in Example 7-15. Example 7-15. Answer to Scenario 7-1 Configuration Question 3 Router A: router ospf 100 network 10.0.0.0 area 0 interface Ethernet 0 ip address 10.1.1.65 255.255.255.224 ip ospf priority 10 ________________________________________________________________ Router B: router ospf 100 network 10.0.0.0 0.255.255.25 area 0 interface Ethernet 0 ip address 10.1.1.66 255.255.255.224 interface Ethernet 1 ip address 10.1.2.1 255.255.255.0 ________________________________________________________________ Router C router ospf 100 network 10.0.0.0 0.255.255.255 area 0 interface ethernet 0 ip address 10.1.1.67 255.255.255.224 interface ethernet 1 ip address 10.1.3.0 255.255.255.0 Note that Router A has been given a priority of 10, ensuring that it becomes the DR. Although this is not essential, it is a clear configuration and is advisable because this router is a larger system and is very reliable. For the same reasons, it is also considered good system management to define the priority for the BDR.