cisco 3 - switches perrine - brierley page 15/10/2015 module 5 switches lan design lan switches

Cisco 3 - Switches

Perrine - Brierley 04/18/23

Module 5

Switches

LAN Design

LAN Switches

Cisco 3 - Switches


Module 5

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

Cisco 3 - Switches


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LAN Design - Availability

Goal to maximise availability

• Throughput

• Response time

• Access to resources

Cisco 3 - Switches


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Layer 1 Design

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

• Fibre?

• Position of MDF/IDF to create appropriate catchment areas

Cisco 3 - Switches


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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

Cisco 3 - Switches


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Layer 3 Design

• Controls traffic flow between network segments

• Logical addressing scheme to separate different network/workgroup functions

• Broadcast control

Cisco 3 - Switches


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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

Cisco 3 - Switches


Module 5

Switches

Cisco 3 - 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.

Cisco 3 - Switches


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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.

Cisco 3 - Switches


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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.

Cisco 3 - Switches


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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.

Cisco 3 - Switches


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Cisco’s design methodology:

1) 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

Cisco 3 - Switches


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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

Cisco 3 - Switches


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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.

Cisco 3 - Switches


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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.

Cisco 3 - Switches


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Layer 2 devices, bridges/switches purposes in the network is to provide:

• flow control

• error detection

• error correction

• reduce congestion

Cisco 3 - Switches


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Asymmetric Switching / Symmetric Switching

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10 Mbps

10 Mbps

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10 Mbps

100 Mbps

10 Mbpsswitch

Cisco 3 - Switches


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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.

Cisco 3 - Switches


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3-layer Model

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Core

Distribution

Access

Other sites/Internet

Campus Backbone

BuildingBackbone

Cisco 3 - Switches


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3-layer Model Core

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

Other sites/Internet

Cisco 3 - Switches


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3-layer Model Distribution

Core

Distribution

• 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

Building backbone

Campus backbone

Cisco 3 - Switches


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3-layer Model Access


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Access

• 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

Cisco 3 - Switches


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Server Placement


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Enterprise Server

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

1

Core

Distribution

Access

Cisco 3 - Switches


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Server Placement


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Enterprise Server

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

1

Core

Distribution

Access

Cisco 3 - Switches


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Server Placement


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Workgroup Server

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

1

Cisco 3 - Switches


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Enterprise servers are placed at the highest layer in the hierarchy.

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

Cisco 3 - Switches


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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

cisco 3 - switches perrine - brierley page 15/10/2015 module 5 switches lan design lan switches

Documents

design criteria

switches routers

functionality design

overall lan design

lan design servers workgroup

lan design availability

design flow control

atm manageability design