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LAN Design
Semester 3, Chapter 4
Allan Johnson
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Table of Contents
Go There!
Go There!
Go There!
Go There!
Go There!
Design Goals & Components
Network Design Methodology
Layer 1 Design
Layer 2 Design
Layer 3 Design
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Design Goals &
Components
Table of Contents
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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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