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 capability 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 2-1 Answers

Using the network address 10.0.0.0, designing a summarized addressing scheme is straightforward.

When the last three octets are written in binary notation, it is easy to determine the bit allocation needed to fulfill the requirements.

Location	Campus	Building	Floor	Hosts
0000	0000	.0000	0000	.00000000

This design provides 16 locations, 16 campuses, and 16 buildings . This would allow 254 hosts per floor or building subnet. Therefore, there is a lot of flexibility in this design for future growth.

1:

Draw the topology map for one of the locations.

A1:

See Figure 2-13.

Figure 2-13. Topology Map of One of the Locations

2:

Using the network address 10.0.0.0, design an addressing scheme that can be summarized. Apply the binary notation for the bit allocation to your diagram.

A2:

See Figure 2-13.

3:

List the range of hosts on one of the subnets allocated to a floor in a building.

A3:

If one of the floors is given the subnet:

Location	Campus	Building	Floor	Hosts
0000	0000	.0000	0000.	.00000000
Subnet in binary notation: 00001010.00010010.00100010.00000000
Subnet in decimal notation: 10.18.34.0
Range of hosts on that subnet: 10.18.34.1 to 10.18.34.254

4:

Indicate how summarization would work within the location.

A4:

Summarization would work within a location because every device and subnet would share the same four high-order bits of the second octet. The following example demonstrates this:

Location	Campus	Building	Floor	Hosts
Using network 10.0.0.0, the four high-order bits of the second octet identify the location.
00001010.0000	0000	.0000	0000	.00000000
Subnet in binary notation:
00001010.0001	0010 .0010 0010 .00000000
Subnet in decimal notation: 10.18.34.0

The summarized address advertised out of the location router would be 10.16.0.0/12.

5:

Allocate a subnet to be used for VLSM to address the WAN links between the locations.

A5:

Many spare subnets are available in the addressing scheme designed. To address the WAN links, it would be sensible to select one of the subnets allocated to the floors and to reassign it to be further subnetted . For example:

Location	Campus	Building	Floor	Hosts
0000	0000	.0000	0000.	.00000000
Subnet in binary notation: 10000000.10001000.00000000
Subnet in decimal notation: 10.128.128.0/30

This allows 64 subnets, with each subnet allowing two hosts (ideal for point-to-point lines). The use of 128.128 in the second and third octets eases network management by readily identifying the serial connections.

6:

Is it possible to summarize the WAN subnets?

A6:

It would not be easy to summarize these WAN subnets because they have a longer bit pattern than the other subnets beneath them. If summarization is possible, they could be summarized down to 10.128.128.0. It is equally sensible to use any easily recognizable address for WAN links (for example, 10.100.100.0).

Scenario 2-2 Answers

1:

To address this network, what class of address would you apply to the Internet?

A1:

You can address the network using a Class C address.

2:

Could you use VLSM? Give reasons for your answer.

A2:

You can use VLSM as long as you use a routing protocol to support the propagation of the subnet mask. It would be useful to have VLSM for the WAN links, but not essential.

3:

If you could use VLSM, write out the masks that you would deploy in binary notation.

A3:

The bit allocation of the fourth octet could be as follows:

Remote Subnet Locations	Hosts
000	00000

This would allow for six remote subnet locations, with 30 hosts on each subnet. The assumption was that the company was more likely to expand each existing location than to increase the number of remote sites. If the reverse were true, the mask would no longer be appropriate, and a single Class C may no longer be sufficient.

Because there are only three remote sites, with five networks to address and three WAN point-to-point links, and because there are six available subnets, one of the subnets could be further subnetted. This subnet would be used to address the WAN links. Another alternative is to use ip unnumbered on the serial links.

Remote Subnet Locations	Hosts
000	00000
110	00000 taken for WAN links
New mask:
110000	00

This would allow 14 WAN links to be identified.

NOTE

It is possible to address more links with the use of subnet zero.

4:

Could summarization be implemented?

A4:

In this size of a network, summarization is not a concern and would not be possible; also, there is no hierarchy in the physical design.

It should be noted that this design does not allow for much network growth, and the organization might want to consider using a private Class B network. Private addressing is discussed in Chapter 3.