network management - planning and design guidelines

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Network Management Planning and Design Guidelines

Introduction

The first step in designing an internetwork is to establish and documentthe goals off the

design. Design goals include the following:

(i). Functionality: The network must enable the users to meet their individual job

requirements in such a way that the overall business requirements of the organization are

met.

(ii). Scalability: The network must be able to support the needs of the organization even

as the organization grows (in terms of number of users).

(iii). Adaptability: The network should be designed with an eye to future

technologies should support new technologies as they become available (such as Voice-

over-IP).

(iv). Manageability: The network must be manageable. If a highly complex design is

delivered to the network management team, it may require an excessive amount of timeand support to work with network operations personnel. In particular, chances are that

another organization may be in charge of managing the network.

(v). Cost-Effectiveness: The cost of implementing the network must be within agreed-upon budgetary constraints.

Analyze Requirements

Develop Internetwork

Structure (Topology)

Set Up A ddressing and

Nam ing C onventions

Provision the hardware

Deploy Internetwork

Operat ing System(IOS) Features

Implement , M onitor,

Maintain the Network

Internetwork Design M ethodology

Design Methodology

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Hierarchical Design

To properly build an internework that can effectively address a users needs, a three-layerhierarchical model to organize traffic flow is often used shown below and consisting

of the Access, Distribution and Core Layers, each of which serves a function in delivering

network services.

(i). Access Layer

The access layer of the network is the point at which end users connect to the network

also called the desktop layer (this is where users gain access to the company network).The resources users need are available locally (such as file servers). But in many

networks, it is not possible nor will it be a good design to provide users with local

access to all services (such dial-out access to the Web). User traffic for these services isdirected to the distribution layer. The Layer 3 devices (such as routers) that guard the

entry and exit to this layer are responsible for ensuring that local server traffic does not

leak out to the wider network.The principle function of the access layer also called access tier is to connect

workgroups (users grouped on the network based on a community of interest: marketing,

administration, engineering, IT, etc) to the distribution tier (layer).

Design Rule: Move user servers and services down to the access layer.

The Distribution Layer

The distribution layer serves as an aggregation point for access layer devices (it provides

connectivity between several parts of the access layer). It determines access across the

Campus Backbone, and also selectively grants specific access to users and departments. Italso provides restriction ofnetwork advertisements by routing protocols, as well as route

summarization. Network policy is said to be implemented at this layer. The layer is based

on FDDI, Fast Ethernet, Gigabit Ethernet, or ATM.

Design Rule: Implement policy at the distribution layer.

PC PC PC PC PC PC PC PC

Remote workgroups Local workgroups

Campus

Backbone

Building

Backbone

Router

Switch

Core

Distribution

Access

Telecom

service provider

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The Core Layer

The primary function of the core layer is to provide optimal transport between differentsites. The figure below depicts a common core network that connects multiple geographic

networks.

The Core tier is usually implemented as a high-speed WAN: ATM (Asynchronous

Transfer Mode), T1/T3, or Frame Relay. Because of WAN provider tariffs, efficient useof bandwidth in the core is nearly always a concern; route summarization helps reduce

routing updates going through the core. To allow the core to act mainly as a transit pathfor traffic, end stations such as servers are not normally put in the core.

The core tier design mission should be to focus on redundancy and reliability (to ensurecontinuous connectivity). Tradeoffs between cost and reliability have to be analyzed to

know the cost of downtime.

Requests for enterprise services Internet access are processed at thedistribution layer and then the requests are forwarded to the backbone, which simply

provides quick transport to the desired enterprise service.

Design rule:Design the core for optimized transport.

Site A

Site B

Site C

Site D

Core Tier topology

Telecomm Service

Provider

Benefits of a Hierarchical Design Model

A hierarchical design model provides the following characteristics:

(i). Scalability Functions such as route summarizations performed at both the

distribution and core layers help a network scale; also, in a hierarchical model, problems

can be recognized more easily.

(ii). Ease of Implementation With clear functionality assigned to each layer,

network implementation becomes easy. A phased approach can also be employed whendeploying a large network; this is generally most cost-effective due to the cost of

resources. Deploy the core first, then the distribution, and finally the access layers. Using

this approach leads to efficient allocation of engineering resources.

(iii). Ease of Troubleshooting: The functions of each layer being well defined also

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makes problem isolation less complicated. Temporary segmentation of the network to

reduce the scope of the problem is also accomplished without requiring full-scaleenterprise outage.

Hierarchical Design Guidelines:

Guidelines for effective use of the hierarchical design model include the following:

(i). Choose a Hierarchical Model that fits your requirements:

Each network has its own requirements, and while some cases may require thethree layers of the hierarchical model, some may only require two. In many small

networks, a single layer is sufficient.

(ii). Do not place end stations on backbones

A backbone without end stations improves the reliability of the network,

facilitates traffic management, and makes planning for increased bandwidth easier.

(iii). Follow the 80/20 Rule for LAN traffic

That is, 80% of the LAN traffic should be local this is achieved by positioningthe needed servers on the workgroup LAN.

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network management - planning and design guidelines

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