Kevin Dooley - Designing Large-Scale LANs.pdf - Sieci(1) - velumaar

ISBN: 0-596-00150-9

Table of Contents:

1. Networking Objectives

Business Requirements

OSI Protocol Stack Model

Routing Versus Bridging

Top-Down Design Philosophy

2. Elements of Reliability

Defining Reliability

Redundancy

Failure Modes

3. Design Types

Basic Topologies

Reliability Mechanisms

VLANs

Toward Larger Topologies

Hierarchical Design

Implementing Reliability

Large-Scale LAN Topologies

4. Local Area Network Technologies

Selecting Appropriate LAN Technology

Ethernet and Fast Ethernet

Token Ring

Gigabit and 10 Gigabit Ethernet

ATM

FDDI

Wireless

Firewalls and Gateways

Structured Cabling

5. IP

IP-Addressing Basics

IP-Address Classes

ARP and ICMP

Network Address Translation

Multiple Subnet Broadcast

General IP Design Strategies

DNS and DHCP

6. IP Dynamic Routing

Static Routing

Types of Dynamic Routing Protocols

RIP

IGRP and EIGRP

OSPF

BGP

7. IPX

Dynamic Routing

General IPX Design Strategies

8. Elements of Efficiency

Using Equipment Features Effectively

Hop Counts

MTU Throughout the Network

Bottlenecks and Congestion

Filtering

Quality of Service and Traffic Shaping

9. Network Management

Network-Management Components

Designing a Manageable Network

SNMP

Management Problems

10. Special Topics

IP Multicast Networks

IPv6

Security

Appendix: Combining Probabilities

Chapter 1. Networking Objectives

The American architect Louis Henry Sullivan described his design philosophy with the simple statement

"form follows function." By this credo he meant that a structure's physical layout and design should reflect

as precisely as possible how this structure will be used. Every door and window is where it is for a reason.

He was talking about building skyscrapers, but this philosophy is perhaps even more useful for network

design. Where building designs often include purely esthetic features to make them more beautiful to look

at, every element of a good network design should serve some well-defined purpose. There are no

gargoyles or frescos in a well-designed network.

The location and configuration of every piece of equipment and every protocol must be carefully

optimized to create a network that fulfills the ultimate purposes for which it was designed. Any sense of

esthetics in network design comes from its simplicity and reliability. The network is most beautiful when it

is invisible to the end user.

So the task of designing a network begins with a thorough study of the required functions. And the form

will follow from these business requirements.

1.1 Business Requirements

This is the single most important question to answer when starting a network design: why do you want to

build a network? It sounds a little silly, but frequently people seem confused about this point. Often they

start building a network for some completely valid and useful reason and then get bogged down in

technical details that have little or nothing to do with the real objectives. It is important to always keep

these real objectives in mind throughout the process of designing, implementing, and operating a network.

Too often people build networks based on technological, rather than business, considerations. Even if the

resulting network fulfills business requirements, it will usually be much more expensive to implement than

is necessary.

If you are building a network for somebody else, then they must have some reason why they want this

done. Make sure you understand what the real reasons are. Too often user specifications are made in terms

of technology. Technology has very little to do with business requirements. They may say that they need a

Frame Relay WAN, or that they need switched 100Mbps Ethernet to every desk. You wanted them to tell

you why they needed these things. They told you they needed a solution, but they didn't tell you what

problem you were solving.

It's true that they may have the best solution, but even that is hard to know without understanding the

problem. I will call these underlying reasons for building the network "business requirements." But I want

to use a very loose definition for the word "business." There are many reasons for building a network, and

only some of them have anything to do with business in the narrow sense of the word. Networks can be

built for academic reasons, or research, or for government. There are networks in arts organizations and

charities. Some networks have been built to allow a group of friends to play computer games. And there

are networks that were built just because the builders wanted to try out some cool new technology, but this

can probably be included in the education category.

What's important is that there is always a good reason to justify spending the money. And once the money

is spent, it's important to make sure that the result actually satisfies those requirements. Networks cost

money to build, and large networks cost large amounts of money.

1.1.1 Money

So the first step in any network design is always to sit down and list the requirements. If one of the

requirements is to save money by allowing people to do some task faster and more efficiently, then it is

critical to understand how much money is saved.

Money is one of the most important design constraints on any network. Money forms the upper limit to

what can be accomplished, balancing against the "as fast as possible" requirement pushing up from below.

How much money do they expect the network to save them? How much money do they expect it will make

for them? If you spend more money building this network than it's going to save (or make) for the

organization, then it has failed to meet this critical business objective. Perhaps neither of these questions is

directly relevant. But in that case, somebody is still paying the bill, so how much money are they willing to

spend?

1.1.2 Geography

Geography is the second major requirement to understand. Where are the users? Where are the services

they want to access? How are the users organized geographically? By geography I mean physical location

on whatever scale is relevant. This book's primary focus is on Local Area Network (LAN) design, so I will

generally assume that most of the users are in the same building or in connected building complexes. But if

there are remote users, then this must be identified at the start as well. This could quite easily spawn a

second project to build a Wide Area Network (WAN), a remote-access solution, or perhaps a Metropolitan

Area Network (MAN). However, these sorts of designs are beyond the scope of this book.

One of the keys to understanding the local area geography is establishing how the users are grouped. Do

people in the same area all work with the same resources? Do they need access to the same servers? Are

the users of some resources scattered throughout the building? The answers to these questions will help to

define the Virtual LAN (VLAN) architecture. If everybody in each area is part of a self-contained work

group, then the network could be built with only enough bandwidth between groups to support whatever

small amounts of interaction they have. But, at the opposite extreme, there are organizations in which all

communication is to a centralized group of resources with little or no communication within a user area. Of

course, in most real organizations, there is most likely a mixture of these extremes with some common

resources, some local resources, and some group-to-group traffic.

1.1.3 Installed Base

The next major business requirement to determine is the installed base. What technology exists today?

Why does it need to be changed? How much of the existing infrastructure must remain?

It would be extremely unusual to find a completely new organization that is very large, has no existing

technology today, and needs it tomorrow. Even if you did find one, chances are that the problem of

implementing this new technology has been broken down among various groups. So the new network

design will need to fit in with whatever the other groups need for their servers and applications.

Installed base can cause several different types of constraints. There are geographical constraints, such as

the location and accessibility of the computer rooms and LAN rooms. There may be existing legacy

network technology that has to be supported. Or it may be too difficult, inconvenient, or expensive to

replace the existing cable plant or other existing services.

Constraints from an existing installed base of equipment can be among the most difficult and frustrating

parts of a network design, so it is critical to establish them as thoroughly and as early as possible.

Kevin Dooley - Designing Large-Scale LANs.pdf

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: