Identifying and Resolving Network Problems 50 best.pptx

 HARDWARE AND NETWORKSERVICING
Level III
Module Title: Identifying and
Resolving Network Problems
zewdu G. DTVET college 1

General Problem-Solving Model
 When you’re troubleshooting a network environment,
a systematic approach works best. An Unsystematic
approach to troubleshooting can result in wasting
valuable time and resources, and can sometimes make
symptoms even worse. Define the specific symptoms,
identify all potential problems that could be causing
the symptoms, and then systematically eliminate each
potential problem (from most likely to least likely)
until the symptoms disappear.
 The following steps detail the problem-solving process
outlined here:

Step 1.
 when analyzing a network problem, make a clear
problem statement. You should define
the problem in terms of a set of symptoms and potential
causes.
 To properly analyze the problem, identify the general
symptoms and then ascertain what kinds of problems
(causes) could result in these symptoms. For example,
hosts might not be responding to service requests
from clients (a symptom). Possible causes might
include a mis configured host, bad interface cards, or
missing router configuration commands.

Step 2.
 Gather the facts that you need to help isolate(unik)
possible causes.
 Ask questions of affected users, network
administrators, managers, and other key people.
Collect information from sources such as network
management systems, protocol analyzer traces, output
from router diagnostic commands, or software release
notes.

Step 3.
 Consider possible problems based on the facts that you
gathered. Using the facts, you can eliminate some of
the potential problems from your list.
Depending on the data, for example, you might be able
to eliminate hardware as a problem so that you can
focus on software problems. At every opportunity, try
to narrow the number of potential problems so that
you can create an efficient plan of action.

Step 4.
 Create an action plan based on the remaining
potential problems. Begin with the most
likely problem, and devise a plan in which only one
variable is manipulated.

Step 5.
Implement the action plan, performing each step
carefully while testing to see whether the symptom
disappears.

Step 6.
Whenever you change a variable, be sure to gather
results. Generally, you should use the
same method of gathering facts that you used in Step 2
(that is, working with the key people affected, in
conjunction with utilizing your diagnostic tools).

Step 7.
Analyze the results to determine whether the problem
has been resolved. If it has, then the process is
complete.

Step 8.
 If the problem has not been resolved, you must create
an action plan based on the next
most likely problem in your list. Return to Step 4, change
one variable at a time, and repeat the process until the
problem is solved.

Net work problem troubleshooting
strategies and documentation
 Networks can be composed of many types of physical
components, from copper wire or fiber- -optic cables to
wireless Access Points and network adapters, there are
steps you can take to make troubleshooting network
problems a little easier, regardless of their composition.
Although each device, protocol, or standard that is a part of
your network may come with its own tools used for
troubleshooting purposes, it's important to realize that you
should take a structured approach to solving problems on
the network. This chapter introduces a few concepts that
make life much simpler for a network administrator,
including documenting network components, and also
documenting problems (and solutions that work).

Documented Network Is Easier to
Troubleshoot
Some of the important things you should consider as
potential candidates for documenting include the
following:
1. A logical map of the network.This may or may not
match up with the physical way the network is laid
out.
2. A physical map of the network. This documentation
should describe eachphysical component and
illustrate the ways in which the different components
are connected.

Cont..
3. Cabling and patch panel information.When you've got
hundreds of cables in a wiring closet patching together
different physical segments, you'll need to know
whichcable connects this to that.
4. Default settings for computers and other devices on
the network.A spreadsheet is good for this. An
application that manages servers, network
components, and client computers is even better.

Cont..
 5. Listings of applications and the computers or users
that make use of them, as well as
 software versions, patch levels, and so on. Be sure to
know who to contact for a particular application. If you
are a network administrator, you are primarily
responsible for the underlying network. If a particular
application is failing, but the network is up and
running, you need to know who to call. There should
always be a contact on your list for application
managers. A network manager can do only so much.

Cont..
6.Information about the user accounts, and associated
permissions and rights, for the users and user groups
on the network.
7. A network overview.It's nice to be able to give a new
user a document that explains what she needs to know
about the network. This should be a short document
telling the user suchthings as which drives are mapped
to her computer, and which printers offer what
features. This should not be an extensive document
such as the physical and logical maps described earlier
in this list.

Cont..
8. Problem reports.Keep track of problems as they arise, and
document the cause and remedy. No need to solve the same
problem twice! This also includes outage reports— keeping track
of unscheduled downtime for a computer or network device can
tell you over time just how capable the device is.
 A logical map of the network shows the relationships between
components and the flow of information through the network.
 A physical map would show the location of each of the
computers, the hub or switch to which they are connected, and
so on. In general, logical maps can be used to help isolate
configuration or application problems, whereas physical maps
can be used to isolate a problem that affects only a portion of the
network, perhaps a single computer or other device.

Physical Connectivity Problems:
 This section describes how to troubleshoot Layer 1 and 2
physical connectivity issues on LANs such as Ethernet or
Token Ring. Problems can generally be found more quickly
by first troubleshooting at Layer 3 and then working
backward when a physical problem is found or suspected.
Possible problems include these:
1. Configuration is incorrect.
2 Cable is faulty or improperly connected.
3.Wiring closet cross-connect is faulty or improperly
connected.
4. Hardware (interface or port) is faulty.
5. Interface has too much traffic.

Cable Problem:
Cables that connect different parts of a network can be
cut or shorted. A short can happen when the wire
conductor comes in contact with another conductive
surface, changing the path of the signal. Cable testers
can be used to test for many types of cable problems
such as:
 Cut cable, incorrect cable connections, Cable shorts,
Interference level, Connector Problem

Testing Cables
 Things that are usually tested include the following:
 1. Cable length—The physical network topology
restricts the length of certain segments in the network.
If you make your own cables, a common error may
result from trying to tretch the limits of the topology
and create a cable that's just a few meters too long. If a
desktop is just a few meters farther from a switch than
the standard allows, you may get complaints from that
user!

cont
2.Resistance—Electricity encounters resistance as it
travels along a copper wire.
3.Noise— Interference can come from other cables that
are bundled together or from outside sources, such as
fluorescent lighting, nearby welding, strong sources of
electromagnetic frequencies, and other high-voltage
electrical sources located near the network cabling.
4.Attenuation—As the cable encounters resistance
traveling down the wire, and as part of the
signalradiates out of the wire, the signal weakens

Cont..
5.Near-end cross-talk (NEXT)—From the transmission
end of a cable, it is necessary to remove the
surrounding material that encloses the copper wires
and attach each wire to a pin in the cable connector.

CHAPTER 2
Troubleshoot network problems
 NIC: The physical hardware that connects the
computer system to the network media.
 Protocol: The language that the computer systems use
to communicate.
 Network client: The interface that allows the
computer system to speak to the protocol.
 Installing a NIC
 The NIC is your computer system’s link to the network,
and installing one is the first step required to connect
to a network.

cont..
 TCP/IP testing tools
 All versions of Windows come with handy tools to test
TCP/IP. Those that you’re most likely to use in the field
are Ping, IPCONFIG, NSLOOKUP, and TRACERT. All
of these programs are command prompt utilities!
Open a command prompt to run them, if you just
place these commands in the Run command, you’ll see
the command prompt window open for a moment and
then quickly close!

Network identified problem
cmd
 Pingis used to check network connectivity. It sends a packet to the specified
address and waits for a reply.
 Nslookup: is used to query Internet domain name server. It returns a
list of hosts in a
domain or the information for one host.
 Tracert: is used to determine the route taken by packets when they
travel across the
network. It shows where communications between your computer and another
computer are having difficulty.
 NetViewis used to display a list of computers in a workgroup. It shows
the available shared
resources on a network.
 Netstat tells you what your computer is connected. This makes if useful for
seeing if your computer is connected to servers that you don't know about. If
you think that your computer is infected with "Spyware" or certain types of
virus Netstat may help you find them out.

cmd
 Netshell -"One-stop network check"
Netshell is a tool that allows you to check that Windows
is properly setup for networking. It can test many
different aspects of your network connection,
depending on what you have got setup on your system.
 DNS lookups You can test to see if your DNS is
working properly by doing a DNS lookup,
using the command line tool nslookup.
 Telnet is a program that allows you to access and use
other computers remotely.

CHAPTER3 Carry out maintenance
support on identified problem
Network Protocols
In Networking "protocol" usually refers to a set of rules that
define an exact format for
communication between systems. For example the HTTP
protocol defines the format for
communication between web browsers and web servers, the
IMAP protocol defines the
format for communication between IMAP email servers and
clients, and the SSL protocol
defines a format for encrypted communications over the
Internet.

Network Addressing and masking
 Introduction
 In the mid-1990's, the Internet is a dramatically
different network than when it was first established in
the early 1980's. Today, the Internet has entered the
public consciousness as the world's largest public data
network, doubling in size every nine months. This is
reflected in the tremendous popularity of the World
Wide Web (WWW), the opportunities that businesses
see in reaching customers from virtual storefronts, and
the emergence of new types and methods of doing
business. It is clear that expanding business and social
awareness will continue to increase public demand for
access to resources on the Internet.

IP(Internet Protocol) Addresses
 An IP address is a logical address of a computer which
is expressed as a four 8-bit group of bits (a total of 32
bits) separated by periods. Each 8-bit group of bits can
be represented by a 3-digit decimal that spans between
0 and 255. For example 196.27.22.42 is a typical IP
address of the DNS server of the Ethiopian
Telecommunication Corporation (ETC). The total
number of distinct addresses one can have from these
32 bit addressing scheme is 232 = 4,294,967,296.
 IP Addressing Class

IP Addressing Class
 When IP was first standardized in September 1981, the
specification required that each system attached to an
IP-based internet be assigned a unique, 32-bit Internet
address value. Some systems, such as routers which
have interfaces to more than one network, must be
assigned a unique IP address for each network
interface.

length of the network-prefix
Class A Networks (/8 Prefixes)
Each Class A network address has an 8-bit network-
prefix with the highest order bit set to 0 and a seven-
bit network number, followed by a 24-bit host-
number. Today, it is no longer considered 'modern' to
refer to a Class A network. Class A networks are now
referred to as "/8s" (pronounced "slash eight" or just
"eights") since they have an 8-bit network-prefix.

Cont
 A maximum of 126 (27 -2) /8 networks can be defined.
The calculation requires that the 2 is subtracted
because the /8 network 0.0.0.0 is reserved for use as
the default route and the /8 network 127.0.0.0 (also
written 127/8 or 127.0.0.0/8) has been reserved for the
"loopback" function.

Class B Networks (/16 Prefixes)
 Each Class B network address has a 16-bit network-
prefix with the two highest order bits set to 1-0 and a
14-bit network number, followed by a 16-bit host-
number. Class B networks are now referred to as"/16s"
since they have a 16-bit network-prefix. A maximum of
16,384 (214 ) /16 networks can be defined with up to
65,534 (216 -2) hosts per network. Since the entire /16
address block contains 230 (1,073,741,824) addresses, it
represents 25% of the total IPv4 unicast address space.

Class C Networks (/24 Prefixes)
 Each Class C network address has a 24-bit network-
prefix with the three highest order bits set to 1-1-0 and
a 21-bit network number, followed by an 8-bit host-
number. Class C networks are now referred to as "/24s"
since they have a 24-bit network-prefix. A maximum of
2,097,152 (221 ) /24 networks can be defined with up
to 254 (28 -2) hosts per network. Since the entire
/24 address block contains 229 (536,870,912)
addresses, it represents 12.5% (or 1/8th) of the total
IPv4 unicast address space.

Dotted-Decimal Notation
 To make Internet addresses easier for human users to
read and write, IP addresses are often expressed as four
decimal numbers, each separated by a dot. This format
iscalled "dotted-decimal notation." Dotted-decimal
notation divides the 32-bit Internet address into four
8-bit (byte) fields and specifies the value of each field
independently as a decimal number with the fields
separated by dots. Figure 5 shows how a typical /16
(Class B) Internet address can be expressed in dotted
decimal notation.

Subnet Masking
 Applying a subnet mask to an IP address allows you to identify
the network and node parts of the address. Performing a bitwise
logical AND operation between the IP address and the subnet
mask results in the Network Address or Number.
 For example, using our test IP address and the default Class B
subnet mask, we get:
 10001100.10110011.11110000.11001000 140.179.240.200 Class B IP
Address
 11111111.11111111.00000000.00000000 255.255.000.000 Default Class
B Subnet Mask --------------------------------------------------------
 10001100.10110011.00000000.00000000 140.179.000.000 Network
Address

Cont..
 Default subnet masks:
 ClassA-255.0.0.0 11111111.00000000.00000000.00000000
 ClassB-255.255.0.0 -11111111.11111111.00000000.00000000
 ClassC-255.255.255.0 -11111111.11111111.11111111.00000000

More Restrictive (limited) Subnet Masks
 Additional bits can be added to the default subnet mask for a given Class to
further subnet, or break down, a network. When a bitwise logical AND
operation is performed between the subnet mask and IP address, the result
defines the Subnet Address. There are some restrictions on the subnet address.
Node addresses of all "0"s and all "1"s are reserved for specifying the local
network (when a host does not know it's network address) and all hosts on the
network (broadcast address), respectively. This also applies to subnets. A
subnet address cannot be all "0"s or all "1"s. This also implies that a 1 bit subnet
mask is not allowed. This restriction is required because older standards
enforced this restriction. Recent standards that allow use of these subnets have
superceded these standards, but many "legacy" (shap)devices do not support
the newer standards. If you are operating in a controlled environment, such as
a lab, you can safely use these restricted subnets. To calculate the number of
subnets or nodes, use the formula (2^n -2) where n = number of bits in either
field. Multiplying the number of subnets by the number of nodes available per
subnet gives you the total number of nodes available for your class and subnet
mask. Also, note that although subnet masks with non-contiguous mask bits
are allowed they are not recommended.

Cont…
 Example:
 10001100.10110011.11011100.11001000 140.179.220.200 IP
Address
 11111111.11111111.11100000.00000000 255.255.224.000
Subnet Mask
 --------------------------------------------------------
 10001100.10110011.11000000.00000000 140.179.192.000
Subnet Address
 10001100.10110011.11011111.11111111 140.179.223.255
Broadcast Address

Exercises
 A. Subnet mask
 B. Network ID
 C.Number of host addresses
 D.Number of host addresses range
 E. Broadcast address

Exercises
192.168.10.20.1/28
Subnet mask
11111111 11111111 11111111 11110000
Network ID
192.168.20.0
255 255 255 240
How mach host address
2n -2 = 24 2*2*2*2 =16
Network ID
1100000 10101000 00010100 00000001
111111111 1111111111 11111111111 1111110000
1100000 10101000 00010100 00000000
192 168 20 0

Cont..
Subnet mask
255 . 255. 255.240
Number of host addresses
192.168.20.0-192.168.20.16
Number of host addresses range
192.168.20.1 - 192.168.20.15
broadcast address
192.168.20.16

Cont..
 You will sometimes see the term default gatewayon
network configuration screens in Microsoft
 Windows. In computer networking, a default gateway
is the device that passes traffic from the local subnet to
devices on other subnets. The default gateway often
connects a local network to the Internet, although
internal gateways for local networks also exist.

Internet default gateways are typically one of
two types:
1.On home or small business networks with a
broadband routerto share the Internet connection, the
home router serves as the default gateway.
2.On home or small business networks without a router,
such as for residences with dialup Internet access, a
router at the Internet Service Provider location serves
as the default gateway.

What is Network Protocol Analysis and Protocol
Analyzer?
 Network protocol analysis is a process for a program or a
device to decode network protocol headers and trailers to
understand the data and information inside the packet
encapsulated by the protocol. To conduct protocol analysis,
packets must be captured at real time for line speed
analysis or later analysis. Such program or device is called a
Protocol Analyzer.
 Protocol Analyzer can be used both for legitimate network
management or for stealing information off a network.
Network operations and maintenance personnel use
Protocol Analyzer to monitor network traffic, analyze
packets, watch network resource utilization, conduct
forensic analysis of network security breaches and
troubleshoot network problems.

The TCP/IP Stack and the OSI Model
TCP/IP is a suite of protocols and rules. It allows us to
communicate with other computers and devices over a
connection oriented network. What we didn’t cover
was the TCP/IP and OSI model-which helps us
understand the TCP/IP suite in a manner of layers and
modules.

The TCP/IP Model and Modular Design
TCP/IP is responsible for a wide range of activity: it must
interface with hardware, route data to appropriate
places, provide error control, and much more. If you
are starting to think the TCP/IP suite can get
confusing, you wouldn’t be the first.

The Open System Interconnection Model
 The Open System Interconnection Model, more
commonly known as simply OSI, is another model that
can help break the TCP/IP suite into modules.
Technically speaking, it is exactly the same as the
TCP/IP model, except that it has more layers. This is
currently being pushed by Cisco since it aids in
learning the TCP/IP stack in an easier manner.
Likewise, you will see the OSI model on many Cisco
exams.

Cont
Instead of four layers, the OSI model has seven. You can
see a direct comparison of the two models below;
notice that only the Application Layer and Network
Layer are divided into smaller layers, and the Internet
Layer is renamed to the “Network Layer.”

cont

OSI
 Physical Layer –They Physical Layer converts data into streams
of electric or analog pulses-commonly referred to as “1’s and 0’s.”
Data is broke down into simple electric pulses, and rebuilt at the
receiving end.
 Data Link Layer –The Data Link layer provides an interface with
the network adapter,
 and can also perform basic error checking. It also maintains
logical links for subnets, so
 that subnets can communicate with other parts of the network
without problem.
 Network Layer –Much like the Transport Layer of the TCP/IP
model, the Network
 Layer simply supports logical addressing and routing. The IP
protocol operates on the Network Layer.

OSI
 Transport Layer –Since we left out the error and flow control in the Network
Layer, we introduce it into the Transport Layer. The Transport Layer is
responsible for keeping a reliable end-to-end connection for the network.
 Session Layer –The Session Layer establishes sessions between applications on
a
network. This may be useful for network monitoring, using a login system, and
reporting. The Session Layer is actually not used a great deal over networks,
although it does still serve good use in streaming video and audio, or web
conferencing.
 Presentation Layer –The Presentation Layer translates data into a standard
format,
while also being able to provide encryption and data compression. Encryption or
data compression does not have to be done at the Presentation Layer, although
it is commonly performed in this layer.
 Application Layer –The Application Layer provides a network interface for
 applications and supports network applications. This is where many protocols
such as

Network Troubleshooting Process
Network Troubleshooting Process
Step 1 Gather data from thoraces customer
Step 2 Verify the obvious issues
Step 3 Try quick solutions first
Step 4 Gather data from the
Step 5 Evaluate the problem
Step 6 Close with the customer computer and
implement the solution

Planning to computer and net work
disaster
 Definition
 A disaster is defined as a sudden misfortune(dangerce
time) that is ruinous(lost) to an undertaking. This
means that there is little time to react at the time of
the misfortune. Preparations have to have beenmade
in advance. The focus should, therefore, be on disaster
planning.

What Is Disaster Recovery?
In IT, disaster recovery involves a series of actions to be
taken in the event of major unplanned
outages to minimize their adverse effects. Disasters can result
from events such as
 hacker attacks
 computer viruses
 electric power failures
 underground cable cuts or failures
 fire, flood, earthquake, and other natural disasters at a
facility
 mistakes in system administration

Why Is Disaster Recovery
Importance?
 When executed well, disaster recovery procedures save
large sums of money. Disaster recovery can also improve
the quality of human life, and it may even save lives.
 The terrorist attacks of 11 September, for example, caused
large-scale network outages. Among the affected systems
were some of the fiber optic telecommunications services
provided by Verizon.
 Besides the financial impact to Wall Street firms from lost
data connectivity, the loss of Voice contact with friends and
family greatly affected many individuals on that day.

Disaster Recovery Planning
 Disaster Recovery Planning
 The best approach to disaster recovery focuses primarily on
planning and prevention. While the damage resulting from the
events of 11 September could not have been anticipated, many
other more typical disaster scenarios can be analyzed in detail.
 For those events that can't be prevented, an IT disaster recovery
plan takes into account the need to
 Detect the outages or other disaster effects as quickly as possible
 Notify ny affected parties so that they can take action
 Isolate the affected systems so that damage cannot spread
 Repair the critical affected systems so that operations can be
resumed

Disaster Recovery Techniques
 All good IT disaster recovery plans consider the three
main components of operations:
 data
 systems
 people

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