CompTIA Network+ Certification Study Guide part 54 pptx

ChApTEr 11: Network Troubleshooting Tools 520 detailed tools that will show you every aspect about the path that a network packet takes to travel from one computer to another, or to gath

ChApTEr 10: Network Management 516

FIGurE 10.16B

Sample PacketTrap Perspective

capture (Permission granted by

PacketTrap Perspective)

FIGurE 10.16C

Sample Event Viewer display

Self Test 517

FIGurE 10.16d

Sample diagram of a network

When planning and establishing your local policies and procedures

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you have to recognize that some state and/or federal regulations

might apply to your organization You are working at the local

county hospital; which of the following regulations should your

organization need to be aware of?

A HIPAA

B Sarbanes-Oxley Act of 2002

C ISO/IEC 27002:2005

D All of the above

You have been delegated the responsibility of creating all of your

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network’s documentation As you research this topic you find out

that you must create CM documentation What types of CM

docu-mentation must you create?

A Wiring schematics, physical/logical network diagrams, baselines,

policies, procedures, configurations, and regulations

B Wiring schematics, physical/logical network diagrams, load

bal-ancing, policies, procedures, configurations, and cache engines

C Wiring schematics, technical network diagrams, baselines,

poli-cies, procedures, configurations, and regulations

D Building schematics, physical/logical network diagrams,

base-lines, policies, procedures, configurations, and regulations

ChApTEr 10: Network Management

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SElF TEST quICK ANSwEr KEy

A

1

D

2

C

3

D

4

B

5

C

6

A

7

A

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B

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D

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B

11

D

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C

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D

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A

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ChApTEr 11

ExAM oBJECTIvES IN ThIS ChApTEr

INTroduCTIoN

Throughout this exam guide, we’ve talked about the fundamentals of network

protocols and network operating systems In this chapter, we’ll bring together

that knowledge to help you in troubleshooting any errors or problems that

occur on your network We’ll begin by talking about the overall methodology

that you’ll use to troubleshoot a network This begins with gathering

infor-mation about a problem to try to determine its cause You’ll then use your

understanding of networking concepts as well as your knowledge of how

your particular network is configured, to isolate the point where the problem

is occurring By eliminating points of failure in a systematic fashion, you

can eliminate trouble spots one by one, until you’ve located the cause of the

problem Maintaining accurate documentation of the physical layout of your

network is essential for this process, as is having a firm grasp of the layers of

the Open Systems Interconnect (OSI) model and the devices that operate at

the various layers

To help you in troubleshooting your network, there are many software

utilities for both the Windows and Linux operating systems that will assist

you in pinpointing the exact nature of a failure You’ll start with tools that

will test basic network connectivity to determine if two computers can

communicate with each other in any way You can then move onto more

Network Troubleshooting Tools

ChApTEr 11: Network Troubleshooting Tools

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detailed tools that will show you every aspect about the path that a network packet takes to travel from one computer to another, or to gather detailed information about name resolution issues You also have access to a wide range of testers for physical network components such as network cables and wall jacks By combining a broad understanding of networking concepts with specific knowledge of the different troubleshooting tools available to you, you will be able to effectively troubleshoot any issues you might face when administering a network

A TrouBlEShooTING METhodoloGy

Before we talk about specific tools and utilities that you can use to trouble-shoot your network, it’s important that you have an overall structure in place that will help you perform that troubleshooting Unfortunately, networking technologies haven’t advanced to the point that a router will flash up an error message like, “My default gateway is misconfigured, please correct

this.” Instead, it is up to you to determine what a problem is before you’ll be

able to go about fixing it When you’re troubleshooting a problem relating to network connectivity, you need to have an understanding of your network

as a whole so that you can determine where the trouble is occurring One of

the key factors in network troubleshooting is isolating the issue to figure out

whether it’s being caused by a single workstation or cable, or if it’s a larger issue affecting numerous users on your network

You can break down the troubleshooting process into two major steps: Gathering information

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Analyzing the information you’ve gathered

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Gathering Information About a problem

To troubleshoot a problem, you first need to identify the problem This can be a challenge when you’re trying to gather information from different users on your network, especially if you’re dealing with a situation where you’re receiving reports of multiple problems at the same time You need to determine which component of your network is causing the issue; this can

be a physical component like a network cable, or a logical component like the Internet Protocol (IP) configuration for a particular network interface card (NIC) You’ll use the information you gather to determine which component

of your network has failed or is misconfigured

A Troubleshooting Methodology 521

Your first step should be to gather information from your users about the

nature of the problem Some questions you’ll probably want to ask include

the following:

1 What is the exact nature of the problem? Try to be as specific as

possible when making this determination For example, you may

get a report that your users are unable to browse external hosts

on the Internet To get a better understanding of the problem,

you need to determine if they have lost all physical connectivity

to the outside world, or if it’s only a specific application that

isn’t functioning Your troubleshooting steps will be different if

a user can ping outside hosts, but not connect to a specific Web

server, versus not being able to connect to the outside world in

any way

2 How many computers are affected by this problem? If the

issue is isolated to a single computer, it is likely that the cause

of the problem will be related to the computer itself If it is

affecting all computers on a particular subnet or those connected

to a particular hub or switch, you can use this information to

help you in the troubleshooting process You can probably tell

from this that your troubleshooting will be far more successful if

you have detailed information about your network’s physical

topology Because of this, one of the most critical documents

you can have on hand when troubleshooting, is a network

dia-gram detailing the physical layout of your network You should

also maintain some type of database containing the IP address

configuration of your routers, switches, servers, and

worksta-tions

3 When did the problem begin to occur? More specifically, you

should find out what changed on the network when the issues

first began If your users began to experience connectivity

issues after you installed a new router, your first step will be to

check the configuration of the router Sometimes this can take

a certain amount of investigation, as you may not be aware

of everything that’s being administered or modified on a large

network Your Internet Service Provider (ISP) might have made

some changes that you’re not aware of, which might be

caus-ing the connectivity failures

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Analyzing and responding to a problem

Now that you’ve collected information about the problem, you need to analyze all of it to determine the cause You should examine every layer

in the OSI model starting at Layer 1 Check your physical layer

connec-tivity, such as cables, patch panels, wall jacks, and hubs Work your way

up to Layer 2, verifying that any switches or switch ports are configured properly At Layer 3 you’ll verify that your routers are configured and func-tioning properly, and then move onto troubleshooting the actual application itself at the transport layer and beyond In almost all cases, it’s best to start

at the physical layer and work your way up so that you’re eliminating the lowest common denominator as a potential issue before moving onto more complex troubleshooting problems If two computers aren’t communicating simply because a cable is unplugged, you can save yourself quite a bit of time

by starting with the physical layer and working up from there

You’ll then want to determine the proper troubleshooting tool to use We’ll spend the majority of this chapter talking about the different tools available for your use, but as a rule you should start with basic connectivity

tools like ping, moving on to other tools once you’ve determined that basic connectivity is in place The reason we start with ping is because it is simple

to use and lets you determine at a glance if two nodes on your network are able to communicate with each other at the most basic level It also very effectively slices the OSI model in half for you in terms of troubleshooting,

because ping operates at the network layer For example, if you are able to

ping a remote host but you cannot File Transfer Protocol (FTP) to it, then you know that the issue lies somewhere above the network layer, because otherwise ping would not be successful If the ping is unsuccessful, then you know that the issue lies in the network, data link, or physical layers

In Exercise 11.1, we’ll look at a common situation where you might use that you’re troubleshooting a connectivity problem between Computer A, with an IP address of 192.168.1.1 and subnet mask of 255.255.255.0, and Computer B with an IP address of 192.168.2.5 and a subnet mask of 255.255.255.0 – this is illustrated in Figure 11.1 These two computers

FIGurE 11.1 Connectivity Diagram.

ping to investigate a connectivity problem between two computers Let’s say

A Troubleshooting Methodology 523

were able to communicate with each other yesterday, but the two

comput-ers haven’t been able to connect because some changes were made on the

network

ExErcisE 11.1 Troubleshooting a connectivity issue

Examine Figure 11.1 The two workstations depicted in the diagram are not

able to communicate They were able to communicate yesterday, but some

changes have been made on the network and they are no longer able connect

to each other

The first thing you should do is go to Computer A and check

1

things out for yourself Use Computer A to ping 192.168.2.5, the

IP address of Computer B, to confirm that the two computers are

unable to communicate

If you don’t receive a response from Computer B, you need to

2

isolate where the failure is taking place So your next step is

to ping the loopback address, 127.0.0.1 You should remember

from that the loopback address is a virtual IP address that’s used

for troubleshooting the Transmission Control Protocol/Internet

Protocol (TCP/IP) installation on a local PC If you are unable to

ping the loopback address, then TCP/IP is either not installed or has

become corrupted on the local computer If this ping is successful,

the problem does not lie in the TCP/IP stack of Computer A

Next, try pinging another machine on the same network segment

3

as Computer A, such as 192.168.1.2 If you get a response from

another machine on the same segment, you know that your local

machine’s TCP/IP stack is functioning properly, and that Computer

A is able to connect to other computers on the same subnet – this

rules out a malfunctioning NIC or network cable at the physical

layer Next, ping the default gateway for Computer A to determine

if the default gateway is functioning

If your default gateway responds, try pinging another host on

4

the same network segment as Computer B, the computer that’s

failing to respond If you get a response from another computer

on Computer B’s network segment, you know that there are no

problems related to Computer B’s network segment itself

If all of your tests thus far have been successful, but you are still

5

unable to contact Computer B, then you have isolated the problem to

ChApTEr 11: Network Troubleshooting Tools

524

Computer B itself Perhaps the network cable connecting Computer

B to the network has gone bad, its network card has failed or needs a new driver installed or its IP configuration is incorrect

By approaching the problem systematically, you were able to trace the network connectivity from one end of the path (Computer A) to the other (Computer B) Testing at each step of the journey allowed you to isolate exactly where the problem was occurring

CoNFIGurING ANd IMplEMENTING

prioritizing Multiple Issues

Sometimes, you’ll encounter a troubleshooting

situ-ation where you have several problems happening

all at once In fact, this is not uncommon because

multiple problems will often be created by the same

root cause When multiple problems occur

simulta-neously, it’s important to focus on the problem that

has the greatest impact on users For example, if

some of your users are reporting a complete inability

to access any resources, and others are reporting that their network access is only slightly slow, the two problems may or may not be related You should troubleshoot the computers that are experiencing a total lack of network access first, because restoring network connectivity is more critical than removing the occasional occurrence of lag on an otherwise working connection.

Network discovery

Now, in a perfect world you’ll be administering a network that someone has already created detailed configuration diagrams for, so that you’ll know exactly what you’re working with when you need to troubleshoot a problem

In reality, though, we’re usually not that lucky, and network administrators often find themselves taking over networks that have little or no documen-tation in place, or documendocumen-tation that hasn’t been kept up to date Luckily,

there are a number of tools that you can use to perform network discovery,

which will help you to automatically generate documentation about the devices on your network and how they are configured These network dis-covery tools will examine a single IP address or an entire subnet and gather

as much information about the devices on that subnet as possible, including their IP addresses, Media Access Control (MAC) addresses, what type of operating system the device is running, and even what types of applications are installed on the device if it is a server or a workstation computer

There are a number of products available that will perform network dis-covery for you, though the majority of them are paid commercial software and

The OSI Model 525

are not available as free downloads One such product is Lan MapShot from

Fluke Networks and another suite of tools is from SolarWinds that includes

an IP Network Browser to perform automatic network discovery, as shown in

Figure 11.2 If you are taking over a network that has poor or nonexistent

net-work documentation in place, it’s strongly advisable to invest in one of these

network discovery tools; the amount of time it will save you in

troubleshoot-ing network connectivity issues will more than pay for the cost of the tool

ThE oSI ModEl

As you have learned, the OSI model creates a framework that defines how

networking protocols like TCP/IP communicate Network packets are passed

from the physical layer up to the application layer, with each layer adding its

FIGurE 11.2 SolarWinds IP Network Browser.