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Switches - PowerPoint PPT Presentation

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Switches. LAN Design LAN Switches. 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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LAN Design

LAN Switches

Lan design servers


Provide file/print/application services to groups of users

Placed in IDF close to users


Provide enterprise services such as DNS, email, applications

Increasing trend to enterprise servers in organisations

Should be placed in MDF

LAN Design - Servers

Lan design availability

Goal to maximise availability


Response time

Access to resources

LAN Design - Availability

Layer 1 design

Copper medium? – CAT5, CAT5e, CAT6 UTP/STP


Position of MDF/IDF to create appropriate catchment areas

Layer 1 Design

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

Layer 2 Design

Layer 3 design

Controls traffic flow between network segments congestion

Logical addressing scheme to separate different network/workgroup functions

Broadcast control

Layer 3 Design

Hierarchical design model
Hierarchical Design Model congestion

  • 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

Switches congestion


NOTE: congestion

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.


  • First step in designing a LAN congestion

    • 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.


  • One needs to consider the following in overall LAN design: congestion

    • 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.


  • Under congestionsegmentation: 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.


  • Cisco’s design methodology: congestion

    • 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

      • 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


  • Servers congestion:

    • 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


Cisco: between the congestionMDF and IDF, the layer 2 LAN switches should have 100Mbps 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.


  • MDF congestion – 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.



Asymmetric Switching / Symmetric Switching is to provide:

10 Mbps


10 Mbps

10 Mbps

10 Mbps


10 Mbps

100 Mbps


In a pure is to provide: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.


3-layer Model is to provide:

Other sites/Internet



Campus Backbone





3-layer Model Core is to provide:

Other sites/Internet


  • 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


3-layer Model Distribution is to provide:


Campus backbone


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


3-layer Model Access is to provide:

  • where local end users have access to network

  • shared bandwidth

  • switched bandwidth

  • MAC-layer filtering

  • microsegmentation

  • isolate broadcast traffic from the workgroup

  • ACLs & filtering

  • LAN

  • logical segmentation into functions



Server Placement is to provide:



Enterprise Server



Too much traffic for router 1 when enterprise server placed at access layer.


Server Placement is to provide:


Enterprise Server




Less traffic for router 1 when enterprise server placed at distribution layer.


Server Placement is to provide:

Workgroup Server


Workgroup server is placed at access layer of site where the largest concentration of users are located.


Enterprise servers is to provide: are placed at the highest layer in the hierarchy.

Workgroup servers are placed nearest to the group that is using it.