Chapter 19 Testing and Troubleshooting Networks

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Testing and Troubleshooting

Networks

Chapter 19


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Chapter 19 2

Chapter Objectives

Identify the tools used for troubleshooting physical

networks

Perform crimp testing and router testing

Perform loop back test

Use the diagnostic utilities


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Chapter 4 3

Recall

Threats are of two types: Internal and External

Firewall protects the system from unauthorizedaccess of resources

Firewalls are of two types: PacketFilter and Proxy Digital signature is an authentication technique

Encryption is conversion of a plain text documentinto a encrypted form

It is used to provide security to data RAID is a collection of hard disks to share and

replicate data


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Chapter 4 4

Network troubleshooting Tools

The various tools available for checking the networkare:

Software Tools

Hardware Tools

Touchy Tools


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Chapter 4 5

Loopback Test

Signal is transmitted and it echos back

Echo signal compared with original signal

Tests the transmission path and tools used for

transmission Traces a faulty node in network

Requires a loopback plug


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Network Monitors

Detect and display problems present in the network

Provides data related to network traffic

Analyze data traffic to determine various networkproblems that can occur

Chapter 4 6


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Chapter 4 7

LAN Tester - I

Used to test 10, 100 and 1000Base-T Networks

Consists of two units Main unit

Indicates LAN device type i.ehub, switch

Determines speed of LAN andtype of link

Remote Probe

Used to locate faults in a cable


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Chapter 4 8

LAN Tester - II

Functions of LAN tester

Verify PC to hub speed and data transmission

Check hub to hub data transmission

Determines any speed bottlenecks present on 10 and

100 Base-T LANs

Continuously tracks LAN link


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Chapter 4 9

Cable Testers and Certifiers

Checks electricalconnections

Determines if a short or open

circuit is present in the

network

Consists of a source of

current, volt meter and

microcontroller


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Chapter 4 10

Time-Domain Reflectometers

Locates fault in metallic cables

Transmits a pulse through the cable

At every discontinuity, an echo is

reflected back Used to test long cables

Results are displayed on a CRT or

LCD


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Chapter 4 11

Protocol Analyzers - I

It may be a software or hardware device

Captures packets from network

Analyzes captured packets

Analyzes the network traffic

Identifies bottlenecks in network

Operate on network layer

Identifies active systems on network

Removes the faulty system from network


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Chapter 4 12

Protocol Analyzers - II

Types of protocol analyzers Packet analyzer

Capture packets present on the wire and store

them for analyzing later

Does a statistical analysis of the data captured but

it is not its primary function

Statistical analyzers

Gather quantitative data to prepare a report on the

different statistical trends

Does not store the packets for later analysis


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Chapter 4 13

Touchy Tools

Used to identify network problems

Problems are identified using asking various

questions to user

Analyzes current situation and compares it with setof baselines

Adequate knowledge and experience is useful to

determine problems


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Chapter 4 14

Backups

Used to preserves a copy of original files

Should be performed on regular basis

Useful when a data loss occurs

Restores system to previous state


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Chapter 4 15

Baselines

Used to compare the systems current performance

with reference level set by the network administrator

Determines possible network problems

Performance monitor helps to set baselines Monitors both real time as well as historical data

Baselines may change with time


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Chapter 19 16

Troubleshooting Model - I

Steps of troubleshooting model

Establish the symptoms

Isolate the cause of the problem

Establish what has changed that might have causedthe problem

Ask Isolating questions


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Chapter 4 17

Troubleshooting Model - II

Identify the most probable cause

Implement a solution

Test the solution

Recognize the potential effects of the solution Document the solution


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Chapter 4 18

Four layer Model

Four layers model HardwareConsiders all the hardware related issues

Focuses on problems with network devices such as

hubs, switches

ProtocolsDeals with problems related to protocols Checks the installation and configuration of protocols

NetworkConsiders the client and server concept

Determines which node will act as client and which will

act as server Shared ResourcesDetermines which resources are

to be shared


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Cable Testing and Certification - I

Cable Distance Measures the distance of a cable and helps to locate

the point where a short or open is present

Speed of pulse depends on wires, type of insulation

and external shielding Wire Map

Used for twisted-pair installations

Detects split pairs

Detects crossed pair condition


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Cable Testing and Certification - II

Attenuation Reduction in strength of signal

Cable Testers are used to measures loss of power

Near-End Crosstalk

Transfer of electricity from one wire to another in the

same cable

Causes

Untwisted patch cables

Crossed pairs


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Cable Testing and Certification - III

Network Monitoring and Protocol Decoding Cable checkers monitor network traffic

Detects high or low level traffic

Locates loose cables

Noise-Level Test

External signal that interfere with original signals

Measured in millivolts (mV)

Testing Fiber Fiber-optic cable testers use optical time-domain

reflectometer which depend on the reflection of light


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Chapter 4 22

SNMP

Simple Network Management Protocol

Networking standard protocol

Used with TCP/IP networks

Monitors and manages the network Helps to examine network performance

Detect network faults or inappropriate access


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Chapter 4 23

Potential Network connectivity

problem

Causes of network connectivity problems

Incorrect network adapters (NIC)

Incorrect switch settings

Faulty hardware

Driver issues

Upgradation of operating system

Server relocation The network adapter is incompatible with the

motherboard


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Chapter 4 24

Network Workstation Troubleshooting

Process Steps to troubleshoot network workstation

Determine what stopped working

Determine if failure is on a single users workstation

Try to log onto the network

Check the NICs link light


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Chapter 4 25

Case Study - I

In the MoneyMaker bank a new computer is connected

in the Customer Service department of Chennaibranch. The computer is connected to the local

network. But it is unable to connect to the Internet.


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Chapter 4 26

Problem

Unable to connect computer to the Internet


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Chapter 4 27

Suggested Solution

Add the new DNS address provided by the network

administrator in the DNS server box


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Netstat Command

Displays TCP/IP information

Determines which ports are active

Identifies ports that are vulnerable to attacks

Provides connection details Provides data about TCP and UDP


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Ipconfig Command

Displays all network settings

Identifies DHCP problems

Used with windows 2000 and later versions

Displays and resets DNS cache Sets and displays DHCP class IDs for an adapter


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Winipcfg Command

Provides IP addressing details

Used for windows 98 or earlier versions

Provides details such as IP address, Subnet Mask,

Default Gateway, DHCP Server, WINS Server, etc.


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ARP Command

Links IP address of a node with its hardware

address

Various ARP command options can be used to

display or change the values in ARP table


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Nbtstat Command

Resolves NetBIOS name resolution problems

Used when WINS server is not accessible

displays protocol information and current TCP/IP

connection using NetBIOS over TCP/IP (NBT)


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Route Command

Allows you to view and make changes in the IP

routing table

Used to differentiate between routes to hosts and

routes to networks by reading the network addressof the destination


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Chapter 4 34

Case Study - II

The employees of MoneyMaker bank have been

constantly complaining that they are not able to get

connected to a particular device. To check theproblem, John who is the network administrator of

the branch performs a ping test. While performing

the ping test he gets Request timed out error


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Chapter 4 35

Problem

Pinging to a device gives request time out error


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Chapter 4 36

Suggested Solution

Ping to the loop back address or do a self ping

Ping to the gateway

If you get a destination host unreachable error

message then gateway address in TCP/IP is notconfigured properly

Ping to the device

If you are still getting the request time out error

then the device is either shut down or not working

properly


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Chapter 4 37

Summary - I

Loopback test is used to test if the ports are

functioning properly

Cross over cables temporarily connect devices

when router, switch or hub is not present Faults in cables like twisted wire pairs, coaxial

cables can be located using time-domain

reflectometer

Network monitor provides information related tonetwork traffic.


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Chapter 4 38

Summary - II

Protocol analyzers perform the function of

interpreting the contents of the packets that are

intercepted

Ping, tracert, netstat, ipconfig, and winipcfg aresome commands that can be used to troubleshoot

various network problems

Netstat is used to check the ports that are active on

your system Ipconfig provides information related to TCP/IP

connection


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Ch 4 39

Summary - III

Ipconfig is used for Windows 2000 or later versions

Winipcfg is used for windows 98 or other versions

ARP links IP address of node to its physical address

Chapter 19 Testing and Troubleshooting Networks

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