What two methods discussed in this chapter could be used by D’Artagnan to determine that Route...

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Chapter 3: Understanding the OSI Reference Model



Task 3 for Scenario 3-1

D’Artagnan sends a packet to Porthos (source group-1.local-M, destination group-6.local-M).

D’Artagnan sends this packet inside an Ethernet frame to Router A. Given this information,

determine the following:

1. What two methods discussed in this chapter could be used by D’Artagnan to determine



that Router A is the router to send this packet to?

2. List the routing table entries in each router that are necessary for the packet to be delivered



to Aramis.

3. What type of data-link header or trailer is discarded by each router in that route?

4. What destination-only data link address is placed into the new data-link headers by each



router?

5. What routes must be in which routers to ensure that Aramis can send a return packet to



D’Artagnan?



04.35700737 CH03 Page 115 Wednesday, February 17, 1999 2:45 PM



Answers to Task 2 for Scenario 3-1

1



115



Scenario Answers

Answers to Task 1 for Scenario 3-1

Based on the network design illustrated in Figure 3-19, Task 1 for Scenario 3-1 asks you to

create the routing table in Router A; assume that all parts of the network are up and working

properly. The routing table for Router A is as follows:

Group



Outgoing Interface



Next Router



group-1



Ethernet 0



N/A



group-2



serial 0



N/A



group-3



serial 0



group-2.local-B



group-4



serial 0



group-2.local-B



group-5



serial 1



N/A



group-6



serial 1



group-5.local-D



group-7



serial 1



group-5.local-E



Answers to Task 2 for Scenario 3-1

Based on the network design illustrated in Figure 3-19, Task 2 for Scenario 3-1 states that

D’Artagnan sends a packet to Porthos (source group-1.local-M, destination group-6.local-M).

D’Artagnan sends this packet inside an Ethernet frame to Router A. The following are the

solutions to exercises 1 through 5 for Task 2.

1. Either the use of a default route or the use of a RIP request to broadcast asking for a router



to reply.

2. The routes to the attached groups used in the routes to group-4 must also be included. The



routing tables are as follows:

In Router A:

Group



Outgoing Interface



Next Router



group-2



serial 0



N/A



group-4



serial 0



group-2.local-B



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Chapter 3: Understanding the OSI Reference Model



In Router B:

Group



Outgoing Interface



Next Router



group-3



Ethernet 0



N/A



group-4



Ethernet 0



group-3.local-C



Group



Outgoing Interface



Next Router



group-4



Token ring 0



N/A



In Router C:



3. Router A discards the Ethernet and adds an HDLC header. Router B discards the HDLC



header and adds an Ethernet header. Router C discards the Ethernet and adds a Token Ring

header.

4. Router A places the never changing HDLC address (Hex 03) into the header. Router B



places Router C’s Ethernet MAC address into the destination address field. Router C

places Aramis’s Token Ring MAC address into the destination address field.

5. This is all noise if Aramis cannot get a packet back to D’Artagnan. The following routing



tables show the routes needed for both directions:

In Router A:

Group



Outgoing Interface



Next Router



group-1



Ethernet 0



N/A



group-2



serial 0



N/A



group-4



serial 0



group-2.local-B



Group



Outgoing Interface



Next Router



group-1



serial 0



group-2.local-A



group-2



serial 0



N/A



group-3



Ethernet 0



N/A



group-4



Ethernet 0



group-3.local-C



In Router B:



04.35700737 CH03 Page 117 Wednesday, February 17, 1999 2:45 PM



Answers to Task 3 for Scenario 3-1



117



In Router C:

Group



Outgoing Interface



Next Router



group-1



Ethernet 0



group-3.local-B



group-3



Ethernet 0



N/A



group-4



Token ring 0



N/A



Answers to Task 3 for Scenario 3-1

Based on the network design illustrated in Figure 3-19, Task 3 for Scenario 3-1 states that

D’Artagnan sends a packet to Porthos (source group-1.local-M, destination group-4.local-M).

D’Artagnan sends this packet, inside an Ethernet frame, to Router A. The following are the

solutions to exercises 1 through 5 for Task 3.

1. Either the use of a default route or the use of a RIP request to broadcast asking for a router



to reply.

2. The routes to the attached groups used in the routes to group-6 must also be included. The



routing tables are as follows:

In Router A:

Group



Outgoing Interface



Next Router



group-5



serial 1



N/A



group-6



serial 1



group-5.local-D



Group



Outgoing Interface



Next Router



group-6



Ethernet 0



N/A



In Router D:



3. Router A discards the Ethernet and adds a Frame Relay header. Router D discards the



Frame Relay header and adds an Ethernet header.

4. Router A places the Frame Relay DLCI for the VC connecting it to router D into the



address field in the header. Router D places Porthos’s Ethernet MAC address into the

destination address field.

5. This is all noise if Porthos cannot get a packet back to D’Artagnan. The following routing



tables show the routes needed for both directions:



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Chapter 3: Understanding the OSI Reference Model



In Router A:

Group



Outgoing Interface



Next Router



group-1



Ethernet 0



N/A



group-5



serial 1



N/A



group-6



serial 1



group-5.local-D



Group



Outgoing Interface



Next Router



group-1



serial 0



group-5.local-A



group-5



serial 0



N/A



group-6



Ethernet 0



N/A



In Router D:



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Answers to Task 3 for Scenario 3-1



119



05.35700737 CH04 Page 120 Wednesday, February 17, 1999 3:15 PM



The following table outlines the CCNA exam objectives that are reviewed in this chapter.

The numbers shown correspond to the master list of objectives found in Chapter 1, “What

Is CCNA?”



Objective



Description



46



Describe the advantages of LAN segmentation.



47



Describe LAN segmentation using bridges.



48



Describe LAN segmentation using routers.



49



Describe LAN segmentation using switches.



50



Name and describe two switching methods.



51



Describe full- and half-duplex Ethernet operation.



52



Describe network congestion problem in Ethernet networks.



53



Describe the benefits of network segmentation with bridges.



43



Describe the benefits of network segmentation with routers.



54



Describe the benefits of network segmentation with switches.



55



Describe the features and benefits of Fast Ethernet.



56



Describe the guidelines and distance limitations of Fast Ethernet.



57



Distinguish between cut-through and store-and-forward LAN switching.



58



Describe the operation of the Spanning-Tree Protocol and its benefits.



59



Describe the benefits of virtual LANs.



60



Define and describe the function of a MAC address.



05.35700737 CH04 Page 121 Wednesday, February 17, 1999 3:15 PM



CHAPTER



4



Understanding LANs and LAN

Switching

The depth of coverage of LAN-oriented topics on the CCNA exam is an elusive target to

hit. From the sheer volume of CCNA objectives, it might seem that these topics are the most

important on the entire exam. Of course, a closer examination shows that several of these

objectives overlap. The LAN switching topics are not covered in Training Path 2, and an

informal survey I did while writing this chapter showed about eight ICRC courses (Training

Path 2) being offered for every one CRLS course (Training Path 1) by the largest Training

Partners. However, LAN switching is very important in real networks, which is more

evidence that preparing yourself on those topics for the CCNA exam is important.

Products that do not use the IOS are unlikely to be covered on the CCNA exam. The

Training Paths cover several products that are not mentioned at all in the exam objectives,

namely, FastHub 300 and the 1900 and 2820 LAN switches. These products use a different

user interface than the command-line interface (CLI) of the IOS. However, these three

products are not likely to be the key products in typical Cisco installations. The LAN topics

that could be included in the future CCNA exam objectives include Catalyst 5000 series

product details and user interface details. Of course, predicting the future is not easy! If any

other user interface will be covered on the CCNA exam, in my opinion, it will be Catalyst

5000. However, the CCNP exams include detailed coverage of LAN switching and Catalyst

5000 series features. Therefore, Cisco has a dilemma of whether to overlap CCNA with

CCNP if they ever consider adding Catalyst 5000 to the CCNA exam.

So, are you wondering why I have diverged into these opposing opinions about what is on

the test? Well, for this simple reason: You need to make the best decision about what topics

to spend your time studying. My suggestion for how to treat LAN and LAN switching

topics for the CCNA exam are as follows:

1. Concentrate on the tables in this chapter, which summarize the information relating



to all the CCNA objectives listed at the start of this chapter.

2. Concentrate on objectives 47-49, 53, 54, 43, and 59. These are the most likely



objectives to be subject to interpretation, so I will take care to reflect the attitudes from

the courses from which these objectives were directly extracted.

3. Get the CCNA objectives from Cisco’s Web site (http://www.cisco.com) and search



for the word “Catalyst”. If it has been added, go to this book’s Web site at Cisco Press

Online (http://www.ciscopress.com/catalog/title_list.html). I will be posting some

additional materials on this topic, free of charge, if the CCNA covers Catalyst

switches in the future.



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Chapter 4: Understanding LANs and LAN Switching



How to Best Use This Chapter

By taking the following steps, you can make better use of your study time:



•

•



Take the “Do I Know This Already?” quiz and write down your answers. Studies show

retention is significantly increased through writing facts and concepts down, even if you

never look at the information again!



•



Figure 4-1 helps guide you to the next step in preparation for this topic area on the CCNA

exam.



How to Use This Chapter

Do I know this already? Quiz



Application

Presentation



Medium score



Session

Transport



Data Link



Review Chapter

using charts and

Network

tables

Data Link



Physical



Physical



Read Chapter

Network



High score

Host B

Application

High

scorePresentation

want Session

more

review Transport

Skip

NetworkChapter

Data Link

NA2603q3



Low score

Host A



Physical



Router 1

End-of-chapter

exercises



Next Chapter



NA260401



Figure 4-1



Keep your notes and answers for all your work with this book in one place for easy

reference.