Transcript Document 7877894

Module 5
Cisco 3 - Switches
Switches
LAN Design
LAN Switches
Perrine - Brierley
5/27/2016
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Module 5
Cisco 3 - Switches
LAN Design - Servers
Workgroup
– Provide file/print/application services to groups of users
– Placed in IDF close to users
Enterprise
– Provide enterprise services such as DNS, email, applications
– Increasing trend to enterprise servers in organisations
– Should be placed in MDF
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Cisco 3 - Switches
LAN Design - Availability
Goal to maximise availability
• Throughput
• Response time
• Access to resources
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Layer 1 Design
• Copper medium? – CAT5, CAT5e, CAT6
UTP/STP
• Fibre?
• Position of MDF/IDF to create
appropriate catchment areas
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Layer 2 Design
• Flow control, error detection &
correction, reduce congestion
• Reduce collision domain size & effects
of collisions
• Keep collision domains small – ideally
fully switched full-duplex environment
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Layer 3 Design
• Controls traffic flow between network
segments
• Logical addressing scheme to separate
different network/workgroup functions
• Broadcast control
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Hierarchical Design Model
• Core layer – backbone –
no packet manipulation
• Distribution layer –
packet manipulation,
interconnecting
workgroups, Layer 3
switches, enterprise
servers
• Access layer – closest
to user/workgroup –
hosts, switches,
workgroup servers
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Cisco 3 - Switches
Switches
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NOTE:
The following is Cisco’s logical idea of planning
a LAN.
Their design is an approach but not the only
one.
Medium & smaller companies will depend on the
ideas of their people to come up with design
criteria – this is where the Cisco planning criteria
can be used.
This chapter will give additional requirements &
suggestions for your LAN design.
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First step in designing a LAN
• establish & document the goals of the design. It is based on:
• functionality –design must meet the job requirement – must
work; connectivity with reasonable speed & reliability
• scalability – initial design should grow without any major
chances to overall design
• adaptability – design toward the future (Frame Relay over
ATM; SMDS, Switched Multi-megabit Data Service, to ATM)
• manageability – design to facilitate network monitoring &
management
Inter-network design seeks to provide the greatest availability for the
least cost.
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One needs to consider the following in overall LAN design:
• function & placement of servers
• collision detection
• place devices to reduce the collision
• contention refers to excessive collisions on Ethernet caused by
too many devices
• segmentation
• use bridges, switches & routers to separate collision domains
• note for bridges & switches; don’t forward collisions, but still belong
to the broadcast domain
• bandwidth vs. broadcast domains
• bandwidth domain is everything associated with one port on a
bridge /switch. All workstations within one bandwidth domain
compete for the same LAN bandwidth resource.
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Under segmentation: bridges & switches are
used
• results in multiple collision domains
• still a single broadcast domain
Bandwidth domain is everything associated
with one port on a bridge or switch.
For Ethernet switches, a bandwidth
domain is also known as a collision
domain.
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Cisco’s design methodology:
Gather the users’ requirements & expectations
• organization’s history
• operational policies
• what their business is
• who has the authority to make decisions on network changes
2) Analyze requirements
1)
• what are the voice & data requirements; which is in more demand;
affects bandwidth
• requirements of the users
3) Design the layer 1,2,3 i.e. topology
• type of topology – star, extended star (most common; 802.3)
• cabling ( TIA/EIA-568-A); UTP; FIBER
• type of cabling determines the distance of the catchment area
4) Document the logical & physical network implementation
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Servers:
Two distinct classes:
• enterprise server –
• supports all the users on the network by
offering services (e-mail, DNS)
• placed in the MDF
• workgroup server –
• applications for users
• placed in the IDF
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Cisco: between the MDF and IDF, the layer 2 LAN switches
should have 100 Mbps or more allocated for these servers.
Intranet versus the internet is that the public does not
have access to the organization intranet.
When layer 2 bridges or switches are used for
segmentation, they create separate collision domains,
and hence increase bandwidth to individual stations.
A bandwidth domain is everything associated with one
port on a bridge or switch.
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MDF – Main Distribution Facility
• HCC – Horizontal cross-connect
Wiring closet where the horizontal cabling connects to a patch
panel that is connected by backbone cabling to the MDF
IDF – Intermediate Distribution Facility
Used when a second wiring closed is needed because the hosts are
outside of the 100 meter limit. Multiple catchment areas are formed.
The IDF is connected to the MDF.
IDF is connected to the MDF by using vertical cabling, also called
the backbone cabling
• VCC – Vertical cross-connect
Is used to interconnect the various IDFs to the central MDF.
Fast Ethernet, cooper wire ( 100Base-TX) & fiber-optic (100Base-FX) is
used to connect the MDF to the IDF.
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Layer 2 devices, bridges/switches
purposes in the network is to provide:
• flow control
• error detection
• error correction
• reduce congestion
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Asymmetric Switching / Symmetric Switching
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10 Mbps
switch
10 Mbps
10 Mbps
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100 Mbps
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In a pure switched LAN environment, the size of
the collision domain is two hosts.
Routers allows for segmentation of the LAN into
unique physical & logical networks. Routers
provide scalability because they can serve as
firewalls for broadcasts.
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3-layer Model
Other sites/Internet
Core
Campus Backbone
Distribution
Building
Backbone
Access
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3-layer Model
Core
Other sites/Internet
Core
• implemented as WAN
• doesn’t perform any packet manipulation
• no ACLs, nor filtering
• were redundant paths are established
• load sharing & rapid convergence of
routing protocols
• efficient use of bandwidth
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3-layer Model
Distribution
Core
Campus backbone
Distribution
Building backbone
• demarc between access & core layers
• ACLs are added; filtering; packet
manipulation
• VLAN routing
• workgroup access to the core layer
• broadcast/multicast domain definition
• policy-based connectivity (what is
acceptable traffic)
• where remote sites have access
• security
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3-layer Model
Access
• where local end users have access to network
• ACLs & filtering
• shared bandwidth
• LAN
• switched bandwidth
• logical segmentation into functions
• MAC-layer filtering
• microsegmentation
• isolate broadcast traffic from the workgroup
Access
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Server Placement
Core
Distribution
Enterprise
Server
Access
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Too much traffic for router 1 when enterprise server placed at access layer.
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Server Placement
Core
Enterprise
Server
Distribution
Access
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Less traffic for router 1 when enterprise server placed at distribution layer.
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Server Placement
Workgroup
Server
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Workgroup server is placed at access layer of site where the largest concentration of
users are located.
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Module 5
Cisco 3 - Switches
Enterprise servers are placed at the
highest layer in the hierarchy.
Workgroup servers are placed
nearest to the group that is using it.
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Module 5
Cisco 3 - Switches
Cisco suggests the following equipment
for physical design:
• core (routers)
• 12000 7500 7200 7000
• distribution (routers)
• 4500 400 3600
• access (routers)
• 2600 2500 1700 1600
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