year 2 - chapter 4/cisco 3 - module 4 lan design

Copyright 2002 Cisco Press: CCNA Instructor’s Manual www.ciscopress.com

Year 2 - Chapter 4/Cisco 3 - Module 4

LAN Design


LAN Design Goals • Functionality

– The network must work.

• Scalability– The network must be able to grow and contract to

meet the needs of the organization.

• Adaptability– The network must adapt to new technologies.

• Manageability– The network must support network monitoring and

management.


Critical Components of LAN Design

• Function and Placement of Servers• Intranets• Collision Detection (Ethernet)• Segmentation• Bandwidth Versus Broadcast Domains


Server Placement

• Servers can be categorized into two distinct classes:– Enterprise servers

– Workgroup (departmental) servers


Intranets

• Centralized Web Servers (Comparable to Enterprise Servers)

• Limited to Internal Users– Those that have logged in to corporate network

• Accessed by Web Browser• Many Day-to-Day Job Functions on the Web


Collision Detection (Ethernet)

• Legacy Ethernet– Contention refers to excessive collisions caused

by too many devices vying for services.– Broadcasts becomes excessive when:

• Too many client packets looking for services• Too many server packets announcing services• Too many routing table updates• Too many broadcast-dependent protocols, such as ARP,

DHCP, and so forth


Broadcast and Collision Domains


Network Design Methodology

• Gathering Requirements• Analyzing Requirements• Designing the Network Topology

– Designing the Layer 1, 2, and 3 LAN structure– Documenting the logical and physical network


Gathering Requirements• Who will be using the network?

– What resources do they need to access?– What is their level of skill?– What are their attitudes toward computers and

applications?

• What data and processes are mission-critical?• What protocols are allowed on the network?• What desktop hosts (OSs) are supported?• Who has authority over addressing, naming,

topology design, and configuration?• What about the existing computer hardware and

software?– How are these resources currently linked and shared?

• What financial resources are available?– Who controls these resources?


Develop a Physical Topology


OSI Layer 1, 2, and 3 Issues


Layer 1 Topology: Signaling Method, Medium Type, and Maximum Length


MDF in a Star Topology


MDFs and IDFs


Extended Star


10BaseT, 100BaseTX, and 1000BaseX Ethernet

• 10 Mbps (and 100 Mbps) to desktops

• Vertical cabling 100 Mbps (or Gigabit) between MDFs and IDFs

• 100 Mbps (or Gigabit) server to network

• Often multiple links combined into channels to provide increased bandwidth in vertical runs and server connections

Fast Ethernet or Gigabit Ethernet

Fast Ethernet or Gigabit Ethernet


Elements of a Logical Topology Diagram


Cut Sheet


Select Layer 2 Devices


Asymmetric Switching


Switches to Reduce Congestion


Determining the Number of Cable Runs and Drops


Hubs Share (Split) Bandwidth


Switches, Hubs, and Collision Domains

Switches combined with full-duplex create collision-free domains.


Layer 3 Design


VLANs in the Design


Routers Provides Logical Structure to a Network


Diagramming a Standards-Based LAN with Routers


Logical Maps


Addressing Maps


Physical Maps

year 2 - chapter 4/cisco 3 - module 4 lan design

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