Transcript Semester 3 Chapter 4 - Institute of Technology Sligo

Institute of Technology,
Sligo Dept of Computing
LAN Design
Semester 3, Chapter 4
Table of Contents
Design Goals & Components
Network Design Methodology
Layer 1 Design
Layer 2 Design
Layer 3 Design
Institute of Technology,
Sligo Dept of Computing
Design Goals & Components
LAN Design Goals
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Critical to design is insuring a fast and stable
network that will scale well as the organization
grows
Design steps are...
1. Gather & establish design goals based 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
Establish the Design Goals
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Although organizations are unique to the
customer, the following requirements tend to be
generic to all. The network must have...
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Functionality--speed and reliability
Scalability--ability to grow without major changes
Adaptability--easily implements new technologies
Manageability--facilitates monitoring and ease of
management
Critical Components of LAN
Design
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With the emergence of high-speed
technologies and complex LAN
technologies, the following critical
components need addressing in design
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Function & placement of Servers
Collision Detection
Microsegmentation
Bandwidth v. Broadcast domains
Placement of Servers
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Servers now perform special functions and can
be categorized as either...
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Enterprise Servers--supports all users on the
network
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DNS and mail servers
should be placed in the MDF
or...
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Workgroup Servers--supports a specific set of users
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file serving such as specialized databases
should be place in the IDF closest to users
Intranets & Collisions
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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...
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Type of data to be accessed
Server privileges
Outfitting desktops with faster connectivity
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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.
Broadcasts & Segmentation
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Layer 2 devices
segment collision
domains
Layer 3 devices
segment broadcast
domains
Bandwidth v. Broadcast
Domains
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A bandwidth domain is
shared by all devices
on a single switched
port.
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Synonymous with
collision domain
A broadcast domain is
shared by all devices
on a single router
interface.
Institute of Technology,
Sligo Dept of Computing
Network Design Methodology
Gathering & Analyzing
Requirements
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Gathering data
about the
organization
includes the
bullets in the
graphic.
Network Availability
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Network design seeks to
provide the greatest
availability for the least cost.
Factors that affect
availability include...
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Throughput
Response time
Access to resources
In the graphic, what type of
server is each and where
should each be placed?
Physical Topologies
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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.
Institute of Technology,
Sligo Dept of Computing
Layer 1 Design
Ethernet Cable Runs
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The physical cabling (also called the cable plant)
is the most important Layer 1 issue to consider
when designing a network.
Design issues include...
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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.
MDF & Other 568A Acronyms
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Whether the LAN is a star
or extended star, the
MDF is the center of the
star.
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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)
10BaseT and 100BaseT Ethernet
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100 BaseT (also called Fast Ethernet) is now the
standard for connecting IDFs to the MDF.
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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?
Layer 1 Logical Documentation
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Layer 1 logical
documentation is concerned
with...
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exact location of MDF/IDF
type & quantity of cabling
room locations & # of drops
port numbers
cable 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.
Institute of Technology,
Sligo Dept of Computing
Layer 2 Design
Common Layer 2 Devices
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The two most common
Layer 2 devices are...
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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...?

Sizing Collision Domains
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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?
Migrating to 100BaseT
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As long as your workstations all
have 10/100 NICs, increasing
the bandwidth is easy.
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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.
Institute of Technology,
Sligo Dept of Computing
Layer 3 Design
Routers and Design
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Routers provide both
physical and logical
segmentation.
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Physically, routers segment
what?
Logically, routers segment
according to Layer 3
addressing dividing the LAN
into logical segments called
subnets.
VLANs & Broadcast Domains
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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.
Diagramming a LAN with
Routers
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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.
Logical & Physical Network
Maps
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After determining your Layer 1, 2, and 3 design,
you can create your addressing (logical) and
physical maps. These are invaluable. They:
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Give a snapshot of the network
Show subnet mask info
Help in troubleshooting