Chapter 1: LAN Design

Chapter 1

LAN Design

Note for Instructors

These presentations are the result of a collaboration among the instructors at St. Clair College in Windsor, Ontario.

• Thanks must go out to Rick Graziani of Cabrillo College. His material and additional information was used as a reference in their creation.

• If anyone finds any errors or omissions, please let me know at:

• tdame@stclaircollege.ca.

Switched LAN Architecture

When building a LAN that satisfies the needs of a small or medium-sized business, your plan is more likely to be successful if a hierarchical design model is used.

• Divided into discrete layers.

• Each layer has a specific purpose.

• Becomes modular – maintenance, performance.

Switched LAN Architecture

Interfaces with end devices.

• Routers, switches, bridges, wireless access points.

• Provides a means of connecting and controlling which devices are allowed to communicate on the network.

Distribution Layer

• Aggregates (funnels) Access Layer traffic.

• Controls traffic flow with security or routing policies.

• Defines broadcast domains.

• Routing of VLANs (Virtual LANs).

Core Layer

• High speed backbone of the network.

• Must be highly available and redundant.

• Must be capable of quickly forwarding large amounts of data.

• Smaller networks – collapsed model (Core and Distribution).

Medium Sized Business

Logical Layout

Physical Layout

Benefits of a Hierarchical Network

+ Benefits:

• Scalability

• Redundancy

• Performance

• Security

• Manageability

Benefits of a Hierarchical Network

Scalability                                                                                                                                                 
Hierarchical Networks can be expanded easily.

Benefits of a Hierarchical Network

Redundancy

Redundancy at the core and distribution layers ensure availability.

Benefits of a Hierarchical Network

Performance

Link aggregation and high performance distribution and core

switches provide near-wire speed at all layers.

Benefits of a Hierarchical Network

Security

Port security at the access layer and policies at the distribution

layer make the network more secure.

Benefits of a Hierarchical Network

Manageability

Consistency among switches at each layer makes

more simple.

The modular design allows a network to scale easily without

becoming over-complicated or burdensome.

Principles of Hierarchical Network Design

*Just because a network is hierarchical, it doesn’t mean it’s well designed.

+ Network Diameter:

• The number of devices that a packet has to cross before it reaches its destination.

+ Bandwidth Aggregation:

• After the bandwidth requirements of the network are known, links between specific switches can be aggregated or combined to provide higher bandwidth.

+ Redundancy:

• The practice of providing multiple paths to a destination or multiple instances of a device.

Principles of Hierarchical Network Design

+ Network Diameter:                                         • For PC1 to

communicate with PC3, the

data must traverse 6

intermediate switches.

• In this case, the network diameter is 6.

• Each switch introduces some latency.

• In a hierarchical network, network diameter is always

going to be a predictable number of hops between the

source and destination devices.

Principles of Hierarchical Network Design

+ Bandwidth                                              

 Aggregation:

• Link aggregation allows 
multiple switch port links to be 
combined soas to achieve higher 
throughput between switches.

• The determining factor is using link aggregation is the

requirements of the user applications.

What is a Converged Network?

+ A Converged Network is one where voice and video

communications have been combined on a single data

network.

• Legacy Equipment:

• Until now, mainly feasible on large enterprise

networks.

What is a Converged Network?

+  Advanced Technology:

• More popular to medium and small sized businesses.

• Can be a difficult decision considering current

investments in technology.

• Benefit:

• Only one network to manage.

What is a Converged Network?

+ New Options:

• You can now tie voice and video communications directly

into an employee's personal computer system.

• Software integrated on a PC eliminates an expensive

handset.

• Add a webcam and video conference.

Considerations for Network Switches

+ Traffic Flow Analysis:                  

• The process of measuring the

bandwidth usage on a network and

analyzing the data.

• Performance tuning.

• Capacity planning.

• Hardware improvement decisions.

User Community Analysis:

• The process of identifying various groupings of users and

their impact on network performance.

Considerations for Network Switches

+ Data Stores and Data Servers Analysis:

• When analyzing traffic on a network, consider the location

of the data stores and data servers.

• Consider both client-server and server-server traffic.

Switch Features

+ Switch Form Factors:

• When selecting a switch, you need to decide between

• Fixed configuration or modular configuration.

• Stackable or non-stackable.

• The switch form factor (physical size) is important

depending upon where the switch will be installed.

• Wiring closet with limited space.

• Computer room with free standing racks.

• Shelf in a central area.

+  Fixed Configuration Switches:

• Fixed in their configuration.

• You cannot add features or options to the switch beyond

those that originally came with the switch.

Switch Features

+ Modular Switches:

• Offer more flexibility.

• Typically come with different sized chassis that allow for

the installation of different numbers of modular line cards.

• The line cards actually contain the ports.

+ Stackable Switches:

• Interconnected using a special backplane cable that

provides high-bandwidth throughput between the

switches (Cisco StackWise).

• The stacked switches effectively operate as a single,

larger switch.

• Desirable when fault tolerance and bandwidth availability

are critical and a modular switch is too costly to

implement.

Switch Performance

+ When selecting a switch for the access, distribution, or core

layer, consider the ability of the switch to support:

• Port Density.

• Forwarding Rate.

• Bandwidth Aggregation Requirements.

+ Port Density:

• Port density is the number of ports available on a single

switch.

+ Forwarding Rate:

• Defines the processing capabilities of a switch by rating

how much data the switch can process per second.

• If the switch forwarding rate is too low, it cannot

accommodate full wire-speed communication across all

of its switch ports.

• A 48 port Gigabit switch is capable of switching 48

Gigabits of traffic.

+ Forwarding Rate:

• Access layer switches typically do not need to operate at

full wire speed because they are physically limited by

their uplinks to the distribution layer.

• Allows the use of:

• Less expensive, lower performing switches at the

access layer.

• More expensive, higher performing switches at the

distribution and core layers, where the forwarding rate

makes a bigger difference.

+ Link Aggregation:

• As part of bandwidth aggregation, you should determine if

there are enough ports on a switch to aggregate to

support the required bandwidth.

+ Power over Ethernet (PoE):

• Allows the switch to deliver power to a device over the

existing Ethernet cabling.

+ Layer 3 Functionality:

• Switches typically operate at Layer 2 of the OSI Model.