LAN Design

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LAN Design

• Semester 3, Chapter 4
• Allan Johnson

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Table of Contents
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 and stable
  network that will scale well as the organization
  grows
• Design steps are...
• Gather establish design goals based on user
  requirements
• Determine data traffic patterns now in the
  future
• Define Layer 1, 2, 3 devices the LAN/WAN
  topologies
• 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 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

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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 accessed
• Server 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 as users attempt to access the same
  server.
• As weve seen, switches can provide dedicated
  bandwidth to minimize or eliminate collsions.

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Broadcasts Segmentation

• Layer 2 devices segment collision domains
• Layer 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.

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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...
• 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, 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.

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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)

Graphic
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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 100BaseT
  cabling (twisted pair), the distance limitation
  means fiber is most often used
• The 100BaseT standard running on twisted pair 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 cabling
• room locations of drops
• port numbers
• cable labels
• Notice Layer 1s 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.

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Layer 2 Design
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Common Layer 2 Devices

• The two most common Layer 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 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 ports 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
  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 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. They
• Give a snapshot of the network
• Show subnet mask info
• Help in troubleshooting

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Table of Contents
End Slide Show
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What is the diameter of each of the three
catchment areas? (Click on graphic to return to
previous slide)