LAN Design

Semester 3, Chapter 3

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Design Goals & Components

Network Design Methodology

Layer 1 Design

Layer 2 Design

Layer 3 Design

Design Goals & Components

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LAN Design Goals

Critical to design is insuring a fast and stable network that will scale well as the organization growsDesign steps are...1. Gather & establish design goals based on user

requirements2. Determine data traffic patterns now & in the future3. Define Layer 1, 2, & 3 devices & the LAN/WAN

topologies4. Document physical & logical network implementation

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Establish the Design Goals

Although organizations are unique to the customer, 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-speed technologies 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 functions and can be categorized as either... Enterprise Servers--supports all users on the network

DNS and mail serversshould be placed in the MDF

or... Workgroup Servers--supports a specific set of users

file serving such as specialized databasesshould be place in the IDF closest to users

GraphicGraphic

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Intranets & Collisions

Intranets are internal to the organization and are not accessible by the 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 privilegesOutfitting 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 as users attempt to access the same server.

As we’ve seen, switches can provide dedicated bandwidth to minimize or eliminate collsions.

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Broadcasts & Segmentation

Layer 2 devices segment collision domainsLayer 3 devices segment broadcast domains

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Bandwidth v. Broadcast Domains

A bandwidth domain is shared 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.

Network Design Methodology

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Gathering & Analyzing Requirements

Gathering data about the organization includes the bullets in the graphic.

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Network Availability

Network design seeks to provide the greatest availability for the least cost.

Factors that affect availability include...ThroughputResponse timeAccess 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, we concentrate on the star/extended star physical topology which typically uses the Ethernet 802.3 standard.

Why? Because it is the most popular topology used in LANs.

The next three sections, evaluate the extended star by layers.

Layer 1 Design

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Ethernet Cable Runs

The physical cabling (also called the cable plant) is the most important 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 star or extended star, the MDF is the center of the star.From the workstation to the

telecommunications outlet, the patch cable should be no more than 3m.

From their to the patch panel, called the HCC, no more than 90m.

From the patch panel (the HCC) to the switch, no more than 6m.

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MDF & Other 568A Acronyms

When distances to the MDF are more than 100m, an IDF is normally added.

The cable run from the IDF to the MDF is called the VCC and is usually fiber.

VCC is just another name for the backbone.

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

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10BaseT and 100BaseT Ethernet

100 BaseT (also called Fast Ethernet) is now 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 documentation is concerned with...exact location of MDF/IDF type & quantity of cablingroom locations & # of dropsport numberscable labels

Notice Layer 1’s logical documentation shows nothing about logical addressing

The Logical Diagram and Cut Sheet are primary tools for design, but are crucial to the tech who is troubleshooting.

Layer 2 Design

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Common Layer 2 Devices

The two most common Layer 2 devices are...Bridges andLAN 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 environment

using 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 port’s bandwidth by the number of hosts (see graphic).

In a pure switched LAN environment where 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 all have 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 to the IDF’s switch.

In the graphic, the red lines represent migrating to 100Mbps.

Layer 3 Design

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Routers and Design

Routers provide both physical and logical segmentation. Physically, routers segment

what? Logically, routers segment

according to Layer 3 addressing dividing the LAN into logical segments called subnets.

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VLANs & Broadcast Domains

As we learned in Chapter 3, VLAN capable switches help routers contain broadcasts.

The graphic shows two broadcast domains.

Notice there is also two subnets. How do we know that?

The router provides communication between the two VLANs.

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Diagramming a LAN with Routers

Notice in the graphic that the two networks are kept separate by the router.

Each switch serves a different network regardless of the physical location of the devices.

To create another physical network in a structured Layer 1 wiring scheme, simply patch the HCC and VCC into the correct switch.

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Logical & Physical Network Maps

After determining your Layer 1, 2, and 3 design, you can create your addressing (logical) and physical maps. These are invaluable. TheyGive a snapshot of the networkShow subnet mask infoHelp in troubleshooting

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