Answers to Chapter 15 Review Questions

Answers to Chapter 15 Review Questions

1:

This chapter mentioned many advantages to using the multilayer model. List as many as possible.

A:

The advantages of using the multilayer model are as follows:

• Modularity

• Scalability

• Ease of maintenance and troubleshooting

• Improved multicast support

• Deterministic traffic flows

• It is a media-independent design (for example, the core can use either Ethernet or ATM)

• It is very resilient and offers fast failover via intelligent Layer 3 routing protocols

• It provides a high degree of control

2:

This chapter also mentioned many disadvantages to using campus-wide VLANs. List as many as possible.

A:

The disadvantages of using campus-wide VLANs are as follows:

• A lack of hierarchy

• Spanning Tree and other problems can quickly spread and cripple the entire network

• Spanning Tree load blanacing can be extremely difficult if not impossible to implement

• Troubleshooting is difficult

• It is difficult to expand the network

• Connecting multiple VLANs to multiple servers through mutli-VLAN NICs like LANE, ISL, and 802.1Q often results in low performance and can overwhelm the servers with broadcast traffic from many VLANs

• They often require that redundancy be eliminated to achieve stability

3:

List some of the issues concerning management VLAN design.

A:

Some of the issues concerning management VLAN design are as follows:

• Always have separate management and end-user VLANs

• Having loop-free management VLANs can improve stability

4:

What are some factors to be considered when determining where to place Root Bridges?

A:

• Place in the paths of high-bandwidth data flows

• Use devices that can carry the aggregate load presented to Root Bridges

• Use a stable device

• Use centralized Root Bridges to facilitate network simplicity

• Use distributed Root Bridges to increase aggregate throughput at the expense of a more complex network design

5:

List five techniques that are available for campus load balancing.

A:

Five techniques that are available for campus load balancing include:

• The Spanning-Tree Protocol

• HSRP

• IP Routing

• ATM

• EtherChannel

6:

What is the primary difference between using routing switches (MLS) and switching routers in MDF/distribution layer devices?

A:

The primary difference between routing switches and switching routers concerns their handling of Layer 2 and Layer 3 functions. Routing switches are, first and foremost, Layer 2 devices that have been enhanced with a variety of Layer 3 functionality. However, they continue to maintain a strong Layer 2 orientation. As a result, they do not automatically create any Layer 3 barriers in the network (this must be done through manual pruning of VLANs from trunk links). On the other hand, switching routers such as the Catalyst 8500s are essentially high-speed versions of traditional Cisco routers. Therefore, they require no special configuration to partition the network into separate Layer 2 domains (creating a more scalable design).

Note that both types of Layer 3 switches can be used to create essentially identical designs. The distinctions being made here reflect the default behavior of these devices and should be kept in mind when designing and building a campus network.

7:

What are the pros and cons of using ATM?

A:

Table A-1 lists the pros and cons of using ATM.

Table A-1. ATM Pros and Cons

Pros

Cons

High available bandwidth

Complexity

Sophisticated bandwidth sharing

Cost

QoS

Ethernet is growing in sophistication and in its capability to handle features previously only supported by ATM (such as COS/QoS)

Support for timing-critical applications such as voice and video

Many new voice and video applications do not require ATM service

Distance

 

Interoperability