Top-Down Network Design, Second Edition

Selecting Internetworking Devices for a Campus Network Design 341

Selecting Internetworking Devices for a Campus

Network Design

At this point in the network design process, you have developed a network topology and

should have an idea of which segments will be shared with hubs or repeaters, bridged with

bridges or switches, or routed using routers. Table 10-6 provides a review of the major

differences between hubs (repeaters), bridges, switches, and routers.

After you have designed a network topology and made some decisions regarding the

placement and scope of shared, switched, and routed network segments, you should then

recommend actual hubs, switches, bridges, and routers from various vendors. This section

covers selection criteria you can use when making decisions.

Criteria for selecting internetworking devices in general include the following:

• The number of ports

• Processing speed

• The amount of memory

• The amount of latency introduced when the device relays data

Table 10-6 Comparing Hubs, Bridges, Switches, and Routers

OSI Layers

Implemented

How Bandwidth

Domains Are

Segmented

How Broadcast

Domains Are

Segmented

Typical

Deployment

Typical Additional

Features

Hub 1 All ports are in the

same bandwidth

domain.

All ports are in the

same broadcast

domain.

Connects indi-

vidual devices

in small LANs

Autopartitioning to

isolate misbehaving

nodes

Bridge 1–2 Each port delineates

a bandwidth

domain.

All ports are in the

same broadcast

domain.

Connects

networks

User-configured

packet filtering

Switch 1–2 Each port delineates

a bandwidth

domain.

All ports are in the

same broadcast

domain.

Connects indi-

vidual devices

or networks

Filtering, ATM

capabilities, cut-

through processing,

multimedia (multicast)

features

Router 1–3 Each port delineates

a bandwidth

domain.

Each port

delineates a

broadcast domain.

Connects

networks

Filtering, firewalling,

high-speed WAN

links, compression,

advanced queuing and

forwarding processes,

multimedia (multicast)

features

342 Chapter 10: Selecting Technologies and Devices for Campus Networks

• Throughput in packets per second (or cells per second for ATM)

• LAN and WAN technologies supported

• Autosensing of speed (for example, 10 or 100 Mbps)

• Autodetection of half- versus full-duplex operation

• Media (cabling) supported

• Ease of configuration

• Manageability (for example, support for Simple Network Management Protocol

[SNMP] and remote monitoring [RMON], status indicators)

• Cost

• Mean time between failure (MTBF) and mean time to repair (MTTR)

• Support for packet filters and other security measures

• Support for hot-swappable components

• Support for redundant power supplies

• Support for QoS features

• Availability and quality of technical support

• Availability and quality of documentation

• Availability and quality of training (for complex switches and routers)

• Reputation and viability of the vendor

• Availability of independent test results that confirm the performance of the device

For switches and bridges (including wireless bridges), the following criteria can be added

to the first bulleted list in this section:

• Bridging technologies supported (transparent bridging, spanning-tree algorithm,

remote bridging, and so on)

• Advanced spanning-tree features supported (rapid reconfiguration of spanning trees

[802.1w] and multiple spanning trees [802.1s])

• The number of MAC addresses that the switch or bridge can learn

• Support for port security (802.1X)

• Support for cut-through switching

• Support for adaptive cut-through switching

• VLAN technologies supported, such as the Virtual Trunking Protocol (VTP), Inter-

Switch Link (ISL) protocol, and IEEE 802.1Q

• Support for multicast applications (for example, the ability to participate in the

Internet Group Management Protocol [IGMP] to control the spread of multicast

packets)