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CCNA 3 v3.1 Module 5

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CCNA 3 Module 5

Switches/LAN Design

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LAN

• Spans a

single room

Building

set of buildings that are close together

• Campus

Group of buildings on a site and belong to a single organization

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Network Design Requirements

• Functionality of the network

It must work with reasonable speed and reliability

It must allow users to meet their job requirements

• Scalability of the network

Must be able to grow without any major changes to design

• Adaptability of the network

Designed with a vision toward future technologies

• Manageability of the network

It should facilitate network monitoring and management to ensure ongoing stability of operation

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Why have LANs Expanded

• Development of high-speed technologies

E.g., Asynchronous Transfer Mode (ATM)

• Complex LAN architectures

LAN switching

Virtual LANs (VLANs)

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Design consideration to maximize available LAN bandwidth and performance

1. The function and placement of servers

2. Collision detection issues

3. Segmentation issues

4. Broadcast domain issues

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LAN Servers

• Provide

File sharing, Printing, Communication, Application services

• Do not function as workstations

• Run specialized operating systems

NetWare, Windows NT, UNIX, and Linux

• Usually dedicated to one function

E.g., e-mail or file sharing

• Categorized into two distinct classes

Enterprise servers

Workgroup servers

• Layer 2 LAN switches located in the MDF and IDFs should allocated 100 Mbps to these servers

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Enterprise Server

• Supports all the users on the network

service that everyone in an organization would need (centralized function)

• Offers services such as

e-mail

Domain Name System (DNS)

• Placed in the Main Distribution Facility (MDF)

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Workgroup Server

• Supports a specific set of users

services such as

word processing

file sharing

Print services

• Placed in the Intermediate Distribution Facilities (IDFs)

Closest to users accessing the applications

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Bridging and Switching

• Excessive collisions reduce available bandwidth by 35% or 40%

• Segmentation with bridges and switches

Splits 1 collision domain into 2 or more collision domains

Create multiple collision domains

Create a single broadcast domain

Stations can get dedicated bandwidth (microsegmentation)

• Broadcast MAC address

FF:FF:FF:FF:FF:FF

Bridges and switches pass broadcast on

Routers filter broadcasts

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LAN Design Methodology

1. Gather requirements and expectations

Identify any current network problems

Information includes

Organization's history

Current status

Projected growth

Operating policies

Management procedures

Office systems and procedures

Viewpoints of the people using the LAN

requirements allow for an informed estimate of costs and timelines for projected LAN design implementation

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Availability measures the usefulness of the network and is affected by

Throughput

Response time

Access to Resources

2. Analyze requirements and data

User requirements constantly change

Increased need for bandwidth due to

voice and video-based network applications

Assess user requirements

LAN must provide prompt and accurate information

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3. Design the Layer 1, 2, and 3 LAN structure

Star topology or Extended Star topology

Use Ethernet 802.3 CSMA/CD technology

LAN topology design can be broken into

Network layer

Data link layer

Physical layer

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4. Document the logical and physical network implementation

Physical topology is the way the various LAN components are connected together

Logical design is the flow of data in a network and the naming and addressing schemes used in the implementation of the LAN design solution.

Specify the locations of the MDF and IDFDocument the type and quantity of cabling Document spare cablesUseful for troubleshooting

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LAN Design Documents

• OSI layer topology map

• LAN logical map

• LAN physical map

• Cut sheets

• VLAN logical map

• Layer 3 logical map

• Addressing maps

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OSI Layer Topology MAPExtended Star Topology in a Multi-campus Building

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Cut Sheet

Provide detailed documentation of all cable runs•Identification numbers•Port the run is terminated on at the HCC or VCC

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VLAN Logical MAP

Group users by department, team or applicationProvides broadcast containment and securityRouters provide communication between VLANsCombines L2 & L3 technology to limit collisions and broadcasts

Communicates betweenVLANs

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Layer 3 Logical MAP

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Addressing Map

Used in troubleshooting

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Layer 1 Design

• Physical Cabling

Fast Ethernet

100 Mbps, can be full-duplex

Fiber-optic backbone

Cat 5e UTP horizontal runs

TIA/EIA-568-A specifications

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TIA/EIA-568-A•Every device connected to the network should be linked to a central location with horizontal cabling

•Main wiring closet MDF•IDF needed for every 100 m•Vertical cable connects IDF and MDF (normally fiber cable)

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Layer 2 Design

• Provide flow control, error detection, error correction, and to reduce congestion in the network

• Layer 2 devices are bridges and switches

Provide microsegmentation of the network

Reduces the size of collision domains and reduces collisions

Boost performance for a workgroup or a backbone

• Asymmetric Switching can allocate bandwidth on a per-port basis (10-Mbps and 100-Mbps ports )

Provide more bandwidth to vertical cabling, uplinks, and servers

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Asymmetric Switching

In a pure switched LAN the size of the collision domain is 2

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All hosts connected to the shared LAN hub share the same collision domain and bandwidth

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Layer 3 Design• Router is a layer 3 device

create unique LAN segments

dividing networks into subnetworks, or subnets (scalability)

Allow communication between segments based on Layer 3 addressing (IP addressing)

Forwards data packets based on destination addresses

Does not forward LAN-based broadcasts (e.g., ARP requests)

Entry and exit point of a broadcast domain

Stops broadcasts from reaching other LAN segments

Serve as firewalls for broadcasts

Allows for segmentation of the LAN into unique physical and logical networks

Allow for connectivity to wide-area networks (WANs), such as the Internet

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Addressing Scheme should be constant throughout the network

Physical port is used to implement VLAN assignmentVLAN 1 - Ports P1, P4, P6VLAN 2 – Ports P2, P3, P5Router allows communication between VLANs

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Hierarchical Design Model

1. Access layer

Connects end users into the LAN (closest to end user)

Host switches

Workgroup servers

Access layer services provides services such as VLAN membership

2. Distribution layer

Packet manipulation and Interconnecting workgroups

Layer 3 switches

Enterprise servers

3. Core layer

Provides the fastest connection between the distribution points – no packet manipulation

Backbone

Optimal transport between sites

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Hierarchical Design Model

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Access Layer

• Entry point for user workstations and servers to the network

• Access Layer devices are a switch or a hub

Shared bandwidth - Hub

Switched bandwidth - Switch - bandwidth is dedicated

• Access layer functions include

MAC layer filtering - direct frames only to the switch port that is connected to the destination device

Microsegmentation – 2 devices in collision domain

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Distribution Layer

• Provide boundary definition in which packet manipulation can take place

• Networks are segmented into broadcast domains

• Policies can be applied

• Access Control Lists can filter packets

• Isolates network problems to workgroups they occur

Prevents these problems affecting the core layer

• Operate at Layer 2 and Layer 3

• Functions

Aggregation of the wiring closet connections

Broadcast/multicast domain definition

Virtual LAN (VLAN) routing

Any media transitions that need to occur

Security

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The Core Layer

• High-speed switching backbone

Interconnects distribution layers

• Router is used for the Layer 3 function

• Should not perform any packet manipulation

• Use Layer 2 or Layer 3 switching

• Asynchronous Transfer Mode (ATM) or Ethernet switches can be used