TOP-DOWN NETWORK DESIGN

CHAPTER THREE

CHARACTERIZING THE EXISTING INTERNETWORK

Oppenheimer

To judge how to meet expectations for network scalability, performance, and availability

OBJECTIVES

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To learn about the topology and physical structure, and assessing the network’s performance

To describe techniques and tools in characterizing an incumbent network

THE EXISTING NETWORK

We now know where we want to go based on the analysis that was just done

We next need to determine where we are starting from

If this is an entirely new network, this step does not need to be done

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CHARACTERIZING THE NETWORK INFRASTRUCTURE

•Developing a set of network maps and learning the location of major internetworking devices and network segments.

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DEVELOPING A NETWORK MAP

Need to understand the traffic flow by learning the location of major hosts, interconnecting devices and network segments.

Goal is to obtain the network map/maps of the already implemented network.

Tools for developing network map:

Some customer don’t have existing map

Find good network-diagramming tool i.e. Cisco work, HP open view etc..

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GET A NETWORK MAP: PURPOSE

Learn the location of major hosts, interconnection devices, and network segments for better understanding of traffic flow.

Remember! Your aim at this step is to obtain a map (or set of maps) of the already-implemented network.

You are one step ahead if the customers are already have maps for the new network design designer have to check the detailed analysis of business and technical requirements

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INFORMATION TO COLLECT Characterize the existing internetwork in terms of:

Its infrastructure

• Logical structure Logical topology = illustrates the architecture of the network

It can be flat or hierarchical, structured or unstructured, layered or not

Its also describes methods for connecting devices in a geometric shape – star , ring, bus, hub or mesh

Discuss further in chapter 5!!

Physical structure/components

Developing a modular block diagram – figure 3-2 page 69

Addressing and naming

Wiring and media

Architectural and environmental constraints

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GET A NETWORK MAP: INFORMATION TO

COLLECT A network map is the first thing to work on

This map should include

Geographic locations

WAN connections between sites Labeled with type/speed/protocols/media/service provider

Buildings and floors where equipment will be

Connections between buildings and floors Labeled with type/speed/protocols/media

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GET A NETWORK MAP: INFORMATION TO

COLLECT Location of connection points like routers and switches

Internet connections

Remote access points

A baseline will be needed as this will tell you where the network is today

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GET A NETWORK MAP-EXAMPLE

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Gigabit Ethernet

Eugene Ethernet20 users

Web/FTP server

Grants PassHQ

16 MbpsToken Ring

FEP (Front End Processor)

IBMMainframeT1

MedfordFast Ethernet

50 users

RoseburgFast Ethernet

30 usersFrame Relay

CIR = 56 KbpsDLCI = 5

Frame RelayCIR = 56 Kbps

DLCI = 4

Grants PassHQ

Fast Ethernet75 users

InternetT1

CHARACTERIZE ADDRESSING AND

NAMING IP addressing for major devices, client networks, server

networks, and so on

Any addressing oddities, such as discontiguous subnets?

Discontiguous subnet = is a subnet that is divided

Figure 3-3 pg 69 (text book)

Any strategies for addressing and naming?

For example, sites may be named using airport codes San Francisco = SFO, Oakland = OAK

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CHARACTERIZE THE WIRING AND MEDIA

Single-mode fiber

Multi-mode fiber

Shielded twisted pair (STP) copper

Unshielded-twisted-pair (UTP) copper

Coaxial cable

Microwave

Laser

Radio

Infra-red

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WHAT SHOULD BE DOCUMENTED???

• To meet scalability and availability goals for new network design, it is important to understand the cabling and wiring of the existing network.

• documenting the existing cabling can help in designing for an enhancement and identify potential problems.

• It is also good to document the cable distance as this information is useful when selecting data link layer technologies based on distance restrictions

• Should document also the connections between buildings. Include the info on the number of pairs of wires and the type of wiring/wireless tech in use.

• should also indicate the distance between buildings- this help in selecting new cabling , i.e. upgrade from copper to fiber hence the distance between building can be much longer.

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TelecommunicationsWiring Closet

HorizontalWiring

Work-AreaWiring

Wallplate

Main Cross-Connect Room(or Main Distribution Frame)

Intermediate Cross-Connect Room(or Intermediate Distribution Frame)

Building A - Headquarters Building B

VerticalWiring

(BuildingBackbone)

CampusBackbone

CAMPUS NETWORK WIRING

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EXAMPLE: BUILDING WIRING

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ARCHITECTURAL CONSTRAINTS

Make sure the following are sufficient

Air conditioning

Heating

Ventilation

Power

Protection from electromagnetic interference

Doors that can lock

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ARCHITECTURAL CONSTRAINTS

Make sure there’s space for:

Cabling conduits

Patch panels

Equipment racks

Work areas for technicians installing and troubleshooting equipment

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CHECKING A SITE FOR A WIRELESS

INSTALLATION

Wireless site survey – to describe the process of analyzing a site to see if it will be appropriate for wireless transmission.

It starts with a draft WLAN design.

Decide on placement of the wireless access point.

the initial placement of the AP is based on an estimate of the signal loss that will occur between the AP and the users of the AP.

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ISSUES FOR WIRELESS INSTALLATIONS

Reflection-Reflection causes the signal to bounce back on itself.

Absorption-Some of the electromagnetic energy of the signal can be absorbed by the material in objects through which it passes, resulting in a reduced signal level.

Refraction-When an RF signal passes from a medium with one density into a medium with another density, the signal can be bent, much like light passing through a prism.

Diffraction-similar to refraction, results when a region through which the RF signal can pass easily is adjacent to a region in which reflective obstructions exist.

Spreading occurs in the diffraction process

[http://www.ask.com/question/difference-between-refraction-and-diffraction].

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CHECK THE HEALTH OF THE EXISTING

INTERNETWORK Performance

Availability

Bandwidth utilization

Accuracy

Efficiency

Response time

Status of major routers, switches, and firewalls

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0 1 2 3 4 5 6 7

17:10:00

17:07:00

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17:01:00

16:58:00

16:55:00

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Utilization

Tim

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Network Utilization

NETWORK UTILIZATION IN MINUTE INTERVALS

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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

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15:00:00

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Utilization

Tim

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Network Utilization

NETWORK UTILIZATION IN HOUR INTERVALS

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CHARACTERIZE PACKET SIZES

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Node A

Node B

Node C

Node D

Node A Node B Node C Node D

X

X

X

X

CHARACTERIZE RESPONSE TIME

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CHECK THE STATUS OF MAJOR ROUTERS,

SWITCHES, AND FIREWALLS show buffers

show environment

show interfaces

show memory

show processes

show running-config

show version

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TOOLS Protocol analyzers

Multi Router Traffic Grapher (MRTG)

Remote monitoring (RMON) probes

Cisco Discovery Protocol (CDP)

Cisco IOS NetFlow technology

CiscoWorks

Cisco IOS Service Assurance Agent (SAA)

Cisco Internetwork Performance Monitor (IPM)

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SUMMARY Characterize the exiting internetwork before designing

enhancements

Helps you verify that a customer’s design goals are realistic

Helps you locate where new equipment will go

Helps you cover yourself if the new network has problems due to unresolved problems in the old network

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REVIEW QUESTIONS

What factors will help you decide if the existing internetwork is in good enough shape to support new enhancements?

When considering protocol behavior, what is the difference between relative network utilization and absolute network utilization?

Why should you characterize the logical structure of an internetwork and not just the physical structure?

What architectural and environmental factors should you consider for a new wireless installation?

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