Ch04 Lan Design

8/13/2019 Ch04 Lan Design

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LAN Design

Semester 3, Chapter 4

Allan Johnson


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Table of Contents

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Design Goals & Components

Network Design Methodology

Layer 1 Design

Layer 2 Design

Layer 3 Design


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Design Goals &

Components

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LAN Design Goals

Critical to design is insuring a fast andstable network that will scale well as

the organization grows

Design steps are...1. Gather & establish design goalsbased on user

requirements

2. Determine data traffic patterns now & in the future

3. Define Layer 1, 2, & 3 devices & the LAN/WAN

topologies

4. Document physical & logical network implementation


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Establish the Design Goals

Although organizations are unique to thecustomer, the following requirements

tend to be generic to all. The network

must have...

Functionality--speed and reliability

Scalability--ability to grow without major changes

Adaptability--easily implements new technologies

Manageability--facilitates monitoring and ease of

management


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Critical Components of LAN Design

With the emergence of high-speedtechnologies and complex LAN

technologies, the following critical

components need addressing in design

Function & placement of Servers

Collision Detection

Microsegmentation

Bandwidth v. Broadcast domains


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Placement of Servers

Servers now perform special functionsand can be categorized as either...

Enterprise Servers--supports all users on the network

DNS and mail servers

should be placed in the MDF

or...

Workgroup Servers--supports a specific set of users

file serving such as specialized databases

should be place in the IDF closest to users

Graphic


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Intranets & Collisions

Intranets are internal to the organization and are not accessible bythe public over the Internet.

Intranet Servers use browsers to provide access to authorized users.

This has caused an increase in needed bandwidth. Therefore,

design must address...Type of data to be accessedServer privileges

Outfitting desktops with faster connectivity

More processing power

10/100Mbps NICs to provide migration to switched technologies

Collision detection and minimization has become a major concern asusers attempt to access the same server.

As weve seen, switches can provide dedicated bandwidth tominimize or eliminate collsions.


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Broadcasts & Segmentation

Layer 2 devicessegment collisiondomains

Layer 3 devicessegmentbroadcastdomains


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Bandwidth v. Broadcast Domains

A bandwidth domain isshared by all devices on a

single switched port.

Synonymous with collision

domain

A broadcast domain is shared

by all devices on a single

router interface.


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Network Design

Methodology

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Gathering & Analyzing Requirements

Gathering dataabout the

organizationincludes:


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Network Availability

Network design seeks toprovide the greatest

availability for the least cost.

Factors that affect availabilityinclude...

Throughput

Response time

Access to resources

In the graphic, what type of

server is each and where

should each be placed?


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Physical Topologies

In the CCNA curriculum, weconcentrate on thestar/extended star physicaltopology which typically

uses the Ethernet 802.3standard.

Why? Because it is themost popular topology used

in LANs. The next three sections,

evaluate the extended starby layers.


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Layer 1 Design

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Ethernet Cable Runs

The physical cabling (also called the cable plant) is the mostimportant Layer 1 issue to consider when designing a

network.

Design issues include...Type of cable to use (twisted-pair, coax, fiber)

Where to use each type (e.g. fiber on the backbone)

How far each run must travel before being terminated (twisted-pair is

limited to what distance?) In an existing LAN, a cable audit is performed to determine

where upgrading and/or replacement of bad cables is

needed.


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MDF & Other 568A Acronyms

Whether the LAN is a staror extended star, the MDFis the center of the star.From the workstation to the

telecommunications outlet,the patch cable should be nomore than 3m.

From there to the patchpanel, called the HCC, no

more than 90m.From the patch panel (the

HCC) to the switch, no morethan 6m.


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MDF & Other 568A Acronyms

When distances to the MDFare more than 100m, an IDF isnormally added.

The cable run from the IDF to

the MDF is called the VCCand is usually fiber.

VCC is just another name forthe backbone.

By adding more wiring closets(more IDFs), you createmultiple catchment areas(Click of graphic button)

Graphic


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10BaseT and 100BaseT Ethernet

100 BaseT (also called Fast Ethernet) isnow the standard for connecting IDFs to

the MDF.

Although you can run Fast Ethernet over 10BaseT cabling(twisted pair), the distance limitation means fiber is most

often used

The 100BaseT standard running on twisted paid is called

100BaseTX On fiber, it is called what?

What is Gigabit Ethernet called?


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Layer 1 Logical Documentation

Layer 1 logical documentationis concerned with...exact location of MDF/IDF

type & quantity of cabling

room locations & # of drops

port numbers

cable labels

Notice Layer 1s logicaldocumentation shows nothing

about logical addressing The Logical Diagram and Cut

Sheet are primary tools fordesign, but are crucial to thetech who is troubleshooting.


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Layer 2 Design

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Common Layer 2 Devices

The two most commonLayer 2 devices are...

Bridges and

LAN Switches

Both provide the added

benefit of what?

Segmenting collision

domains into microsegments. Switches can also provide connections of unlike

bandwidth (e.g., 100Mbps to the server & 10Mbps to

workstations). This is called...?


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Sizing Collision Domains

In a switched LAN environmentusing hubs, the bandwidth of each

switched port is shared by all the

devices. Therefore, they also share

the same collision domain.

To determine the bandwidth per

host, simply divide the ports

bandwidth by the number of hosts

(see graphic).

In a pure switched LAN environmentwhere each host has its own port,

the size of the collision domain is 2.

If running full-duplex, then the

collision domain is eliminated. Why?


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Migrating to 100BaseT

As long as your workstations allhave 10/100 NICs, increasing the

bandwidth is easy.

Replace the hub with a 100Mbps

capable hub and patch the HCC

into a 100Mbps port on the switch.

In addition, you can add another

100Mbps VCC from the IDF to the

MDF, which provide 200 Mbps tothe IDFs switch.

In the graphic, the red lines

represent migrating to 100Mbps.


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Layer 3 Design

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Routers and Design

Routers provide bothphysical and logical

segmentation.

Physically, routers segment

what?

Logically, routers segment

according to Layer 3

addressing dividing the LANinto logical segments called

subnets.


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VLANs & Broadcast Domains

As we learned in Chapter3, VLAN capable switcheshelp routers containbroadcasts.

The graphic shows twobroadcast domains.

Notice there are also twosubnets. How do we know

that? The router provides

communication betweenthe two VLANs.


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Diagramming a LAN with Routers

Notice in the graphic thatthe two networks are keptseparate by the router.

Each switch serves a

different network regardlessof the physical location ofthe devices.

To create another physical

network in a structuredLayer 1 wiring scheme,simply patch the HCC andVCC into the correct switch.


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Logical & Physical Network Maps

After determining your Layer 1, 2, and 3 design, you cancreate your addressing (logical) and physical maps. These

are invaluable. They

Give a snapshot of the network

Show subnet mask info

Help in troubleshooting


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Table of Contents

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Ch04 Lan Design