Transcript Chapter 1

LAN DESIGN
Akhyari Nasir
TATiUC
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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...
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
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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

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
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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 collisions.
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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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LAN Design Methodology
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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
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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 and IDF
 Short for main distribution frame, a cable rack
that interconnects and manages the
telecommunications wiring between itself and any
number of IDFs (Intermediate Distribution
Frames). Unlike an IDF, which connects internal
lines to the MDF, the MDF connects private or
public lines coming into a building with the internal
network. For example, an enterprise that
encompasses a building with several floors may
have one centralized MDF on the first floor and
one IDF on each of the floors that is connected to
the MDF.
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MDF & Other 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 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)

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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

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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 1’s
logical documentation
shows nothing about
logical addressing
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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
port’s bandwidth by the
number of hosts (see
graphic).

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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.
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Collision and Broadcast domains
 Hub

A hub receives a packet (chunk) of data (a frame in Ethernet
lingo) at one of its ports from a PC on the network, it transmits
(repeats) the packet to all of its ports and, thus, to all of the
other PCs on the network. If two or more PCs on the network
try to send packets at the same time a collision is said to occur.
 Switch

An Ethernet switch automatically divides the network into
multiple segments, acts as a high-speed, selective bridge
between the segments, and supports simultaneous connections
of multiple pairs of computers which don't compete with other
pairs of computers for network bandwidth. It accomplishes
this by maintaining a table of each destination address and its
port.
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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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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.

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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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Switched LANs, access layer
overview
The hierarchical design model includes the following three layers:
 The access layer provides users in workgroups access to the
network.
 The distribution layer provides policy-based connectivity.
 The core layer provides optimal transport between sites.
 The core layer is often referred to as the backbone.
Access layer switches
 Access layer switches operate at Layer 2 of the OSI model and
provide services such as VLAN membership.
 The main purpose of an access layer switch is to allow end users
into the network.
 An access layer switch should provide this functionality with low
cost and high port density.
 Catalyst 1900 series
 Catalyst 2820 series
 Catalyst 2950 series
 Catalyst 4000 series
 Catalyst 5000 series
Distribution Layer
 The purpose of this layer is to provide a boundary definition in which
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packet manipulation can take place.
Networks are segmented into broadcast domains by this layer.
Policies can be applied and access control lists can filter packets.
The distribution layer also prevents problems from affecting the core
layer.
Switches in this layer operate at Layer 2 and Layer 3.
The distribution layer includes several functions such as the following:
 Aggregation of the wiring closet connections
 Broadcast/multicast domain definition
 Virtual LAN (VLAN) routing
 Any media transitions that need to occur
 Security
Distribution layer switches
2926G
6500
 Distribution layer switches are the aggregation points for multiple access
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layer switches.
The switch must be able to accommodate the total amount of traffic from
the access layer devices.
The distribution layer combines VLAN traffic and is a focal point for
policy decisions about traffic flow.
For these reasons distribution layer switches operate at both Layer 2 and
Layer 3.
The following Cisco switches are suitable for the distribution layer:
 Catalyst 2926G
 Catalyst 5000 family
 Catalyst 6000 family
Core Layer
 The core layer is a high-speed switching backbone.
 If they do not have an associated router module, an external
router is used for the Layer 3 function.
 This layer of the network design should not perform any packet
manipulation.
 Packet manipulation, such as access list filtering, would slow down
the switching of packets.
 Providing a core infrastructure with redundant alternate paths
gives stability to the network in the event of a single device
failure.
Core Layer Switches
Lightstrea
8540
m 1010
 In a network design, the core layer can be a routed, or Layer 3, core.
 Core layer switches are designed to provide efficient Layer 3 functionality
when needed.
 Factors such as need, cost, and performance should be considered before
a choice is made.
 The following Cisco switches are suitable for the core layer:
 Catalyst 6500 series
 Catalyst 8500 series
 IGX 8400 series
 Lightstream 1010
Summary
References
 Slides adapted from Allan Johnson, CCNA
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