NETWORK TROUBLESHOOTING

Introduction
In this topic, we will discuss some of the things you should do when a network goes wrong, whether it’s a
personal network or a network that you manage professionally as a network administrator. This topic should
also prepare you to go through a repeatable process in diagnosing and addressing a network issue. The hope
is that, by introducing you to tried and true methods, you can develop experience with network issues and
troubleshoot each issue more quickly than the last.

What is troubleshooting a network?

The term troubleshooting refers to the process of identifying problems with a network through a rigorous
and repeatable process and then solving those problems using testable methods. Troubleshooting is more
effective than trying things at random until the network functions because it allows you to target individual
network components, testing each for function, and encourages you to document your process. Network
troubleshooting is useful for almost anyone, from a computer enthusiast to an aspiring network engineer.
Troubleshooting is the process of solving a problem or determining an issue. Troubleshooting often involves
the process of elimination, where a technician will follow a set of steps in order to determine the problem or
resolve the problem.

Why troubleshooting skills are essential for network management

Network troubleshooting skills are nice to have in the home so you can avoid inconvenience when your
network goes down, but for many businesses, having a professional with network troubleshooting skills on
site is essential. While home network outages may just be an annoyance — preventing you from finishing
your movie on Netflix or delaying your online chat conversation with a friend — network outages in the
workplace can grind many modern businesses, which rely heavily on connectivity, to a halt.

Businesses certainly recognize the importance of maintaining a fully operational network.

While emerging technology tends to make the most headlines and have the most potential for growth, these
technologies cannot provide value without being connected to the overall IT architecture. As an
organization’s technology footprint grows, its network needs will also change, and troubleshooting will
become more challenging and critical.

This time when a network is unavailable is known as network downtime. For a business that operates online,
every minute of downtime is a minute that client communications are hindered, employees can’t access their
data in the cloud and many of the business’s online tools and applications are unavailable.

Common network problems

Performance problems
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Your network has performance problems when it is not operating as effectively as it should. For example,
response times may be slow, the network may not be as reliable as usual, and users may be complaining that
it takes them longer to do their work. Some performance problems are intermittent, such as instances of
duplicate addresses. Other problems can indicate a growing strain on your network, such as consistently
high utilization rates. If you regularly examine your network for performance problems, you can extend the
usefulness of your existing network configuration and plan network enhancements, before a performance
problem adversely affects the users' productivity.

Sources of network slowness

 Poor routing
 Misconfigured router or switch
 Bad cabling
 Over utilized capacity
 Malware running on the network
 Misconfigured circuit between sites
 Excessive use of network protocols
 Electrical interference
 An overloaded server at the remote end of the connection
 Misconfigured DNS

IP address conflicts
Duplicate IP addresses on the network causes problems with correct delivery of data packets. Duplication of
IP addresses can occur when using static IP addresses configured manually. DHCP automatically assigns
TCP/IP addressing to computers when they join the network and automatically renews the addresses before
they expire. The advantage of using DHCP is the reduced number of addressing errors, which makes
network maintenance much easier. Because DHCP IP addressing is automatic and does not assign duplicate
IP addresses, as sometimes happens with manual entries, DHCP is the preferred method of network IP
assignment.

Network congestion
Whether it’s due to a broadcast storm, increasing connections, excessive protocols or over utilization of the
bandwidth, as packets increase latency increases and packets begin to be dropped.

Hardware failure
Troubleshooting hardware infrastructure problems presents a significant challenge. It is often not an easy
task and usually involves many processes, including baselining and performance monitoring. One of the

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keys to identifying the failure of a hardware network device is to know what devices exist on a particular
network and each device's designed function.

Spyware, worms and other malware

Here is another source of bandwidth consumption. Spyware, worms, Trojans and the like perform scanning
operations, install additional protocols and services and communicate with their remote counterparts. These
actions frequently account for a significant and sometimes large amount of bandwidth utilization. You
should be vigilant in keeping your network free of these threats and bandwidth consumers with antivirus
software, firewalls and other protective and/or detection systems.

Misconfiguration
Even the most seemingly insignificant misconfiguration can cause major problems. Incorrect IP address or
subnet mask can render a client unable to communicate. Incorrect DNS, depending on if it is a local DNS
server or and internet DNS server can cause unreliable communication. A mismatch in duplex and/or speed
settings between a router, switch, server or workstation causes slowness for the client device or the whole
network due to dropped packets.

Increased number of connections (network growth)

As the number of devices (workstations, servers, printers, switches, audio/video equipment, etc.) connected
to the network increases so goes the demand for bandwidth. You can balance the load through strategic
placement of progressively higher capacity infrastructure devices and segmenting to control areas of high
traffic. Prioritizing traffic (also called traffic shaping) according to type, source, destination, etc., can help
make better, more efficient use of available bandwidth.

Poor typology design

The physical connections used to create the networks are sometimes at the root of a network connectivity
error. Troubleshooting wiring involves knowing what wiring your network uses and where it is used. When
troubleshooting network media consider: media range (attenuation), throughout limitations, and media
connectors.

Hardware or link failures

These are due to faulty network equipment, bad cabling such as degraded connectors or fiber optics, of
natural events such as wind and flooding.

Internet problems and outages

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They happen almost every day, most of them are regional, others worldwide spread service interruptions.
Even though these issues generally happen outside a private network infrastructure, it’s still important to be
aware of them if they impact the organization.

Network slowness
Network slowness and sluggish application performance could indicate a network congestion issue. When
the traffic originated is higher than what the network is capable of, buffers start filling up, and routers start
dropping packets.

Network configuration errors

Network configuration errors can cause total outages, slowness due to suboptimal configuration, or other
unexpected behaviors. These types of failures can be hard to troubleshoot if the organization doesn’t have a
configuration change management process in place nor a network configuration audit tool.

Wireless
WLANs can experience localized RF (Radio-Frequency) issues such as low signal or interference,
infrastructure issues such as radius authentication failures, or client specific errors.

User error or perception

User error or perception is one of the most common network problems. In the case where it’s not the
network to be at fault, the support team is still required to show a proof of innocence; screenshots from a
network monitoring tool, packet traces, and ping tests will provide the required data to exonerate the
network.

Importance of network troubleshooting

Network troubleshooting is a crucial process for maintaining efficient and reliable computer networks.
Network troubleshooting is a key aspect of network management that enables organizations to:
 Reduced network downtime: Network outages can significantly disrupt business operations, leading to
lost productivity and revenue. Prompt troubleshooting helps identify and resolve network issues quickly,
minimizing downtime and its negative consequences. Efficient troubleshooting will reduce the amount
of network downtime that digital services and information systems experience.
 Improved network performance: Network slowdowns, lagging applications, and connectivity
problems can frustrate users and hinder productivity. Troubleshooting helps pinpoint bottlenecks,
configuration errors, or overloaded resources, allowing for optimization and improved network
performance.

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 Enhanced network security: Network vulnerabilities can expose sensitive data to unauthorized access.
Troubleshooting can help identify security breaches, malware infections, or weak security protocols. By
addressing these issues, you can strengthen your network defenses and prevent security incidents.
 Proactive maintenance: Network problems often don't arise suddenly. Troubleshooting can uncover
potential issues before they escalate into major outages. By addressing these early warning signs, you
can take proactive measures to prevent disruptions and ensure network stability.
 Improved user experience: A reliable and well-functioning network is essential for a positive user
experience. Troubleshooting helps resolve connectivity issues and performance problems, ensuring users
have smooth access to the resources they need.
 Cost savings: Network downtime and ongoing performance issues can incur significant costs. By
resolving problems quickly and preventing future issues, effective troubleshooting helps minimize
expenses associated with network maintenance and lost productivity.
 Improved network management: Troubleshooting provides valuable insights into network behavior
and resource utilization. This information can be used to optimize network configuration, allocate
resources efficiently, and make informed decisions about future network expansion or upgrades.

Basic network troubleshooting steps

Network troubleshooting is a repeatable process, which means that you can break it down into clear steps
that anyone can follow.

1. Identify the problem: The first step in troubleshooting a network is to identify the problem. As a part of
this step, you should do the following:
 Gather information about the current state of the network using the network troubleshooting tools
that you have available to you.
 Duplicate the problem on a test piece of hardware or software, if possible. This can help you to
confirm where your problem lies.
 Question users on the network to learn about the errors or difficulties they have encountered.
 Identify the symptoms of the network outage. For example, do they include complete loss of
network connection? Slow behavior on the network? Is there a network-wide problem, or are the
issues only being experienced by one user?
 Determine if anything has changed in the network before the issues appeared. Is there a new
piece of hardware that’s in use? Has the network taken on new users? Has there been a software
update or change somewhere in the network?
 Define individual problems clearly. Sometimes a network can have multiple problems. This is the
time to identify each individual issue so that your solutions to one aren’t bogged down by other
unsolved problems.

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2. Develop a theory: Once you have finished gathering all the information that you can about the network
issue or issues, it’s time to develop a working theory. While you’re producing your theory about the
causes of the network issue, don’t be afraid to question the obvious, but remain on the lookout for more
serious issues. Sometimes a network outage occurs because someone tripped on a wire or some other
simple problem. However, at other times the problems might be related more complicated causes, like a
breach in network security.
3. Test the theory: Using the tools at your disposal, it’s time to test your theory. If your theory is that the
network router is defective, try replacing it with another router to see if that fixes the issue. At this stage,
it’s important to remember that proving your own theories wrong doesn’t mean that you’ve failed.
Instead, it means that it’s time to return to step two, develop a new theory, and then find a way to test
that one. Sometimes your first theory may be right, but it’s also common to go through several theories
before arriving at the true cause of your network’s issues.
4. Plan of action: Once you’ve confirmed your theory about the causes of the network issues, you’re in a
position to solve them. Come up with a plan of action to address the problem. Sometimes your plan will
include just one step. For example, restart the router. In other cases, your plan will be more complex and
take longer, such as when you need to order a new part or roll a piece of software back to a previous
version on multiple users’ computers.
5. Implement the solution: Now that you have a plan for fixing the network, it’s time to implement it.
There are some solutions that you may be able to do by yourself, while others may require cooperation
from other network administrators or users.
6. Verify system functionality: Once you’ve implemented your solution, be sure to test the network. Make
sure that the issue in question has been resolved, but also be on the lookout for other issues that may
have arisen from the changes that you made to the network. As part of your verification process, make
sure to consult both the network tools at your disposal as well as individual user accounts of their
experiences on the network.
7. Document the issue: If you are a network professional or an enthusiast who is around networks often,
then it’s safe to say that this won’t be the last time you encounter this particular issue. Make sure to
document each stage of troubleshooting the problem, including the symptoms that appeared on the
network, the theory you developed, your strategy for testing the theory and the solution that you came up
with to solve the issue. Even if you don’t reference this documentation, it may be helpful to another
network engineer at your company in the future and could help to shorten network downtime.

Network troubleshooting tools

In addition to user reports and firsthand experience on the network, there are a number of tools available for
you to use when it comes to diagnosing and treating network issues. These tools may exist in the computer’s
operating system itself, as standalone software applications or as hardware tools that you can use to
troubleshoot a network.
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Command-line tools
On Windows PCs, the command prompt can be accessed by searching for it in the start menu or by typing
“cmd” into the Run window. On a Linux system, you can press Ctrl + Alt + T to open the command line.
The following commands can be entered into the command prompt one at a time to reveal specific
information about the network status:
 ping — A TCP/IP utility that transmits a datagram to another host, specified in the command. If the
network is functioning properly, the receiving host returns the datagram.
 tracert/traceroute —A TCP/IP utility that determines the route data takes to get to a particular
destination. This tool can help you to determine where you are losing packets in the network, helping to
identify problems.
 nslookup — A DNS utility that displays the IP address of a hostname or vice versa. This tool is useful
for identifying problems involving DNS name resolution.
 ipconfig — A Windows TCP/IP utility that verifies network settings and connections. It can tell you a
host’s IP address, subnet mask and default gateway, alongside other important network information.
 ifconfig — A Linux or UNIX TCP/IP utility that displays the current network interface configuration
and enables you to assign an IP address to a network interface. Like ipconfig on Windows, this
command will tell you vital information about the network and its status.
 iptables — A Linux firewall program that protects a network. You can use this tool if you suspect that
your firewall may be too restrictive or too lenient.
 netstat — A utility that shows the status of each active network connection. This tool is useful for
finding out what services are running on a particular system.
 tcpdump — A utility that is used to obtain packet information from a query string sent to the network
interface. It’s available for free on Linux but can be downloaded as a command for Windows.
 pathping — A TCP/IP command that provides information about latency and packet loss on a network.
It can help you troubleshoot issues related to network packet loss.
 nmap — A utility that can scan the entire network for various ports and the services that are running on
them. You can use it to monitor remote network connections and get specific information about the
network.
 route — A command that enables manual updating of the routing table. It can be used to troubleshoot
static routing problems in a network.
 arp — A utility that supports the Address Resolution Protocol (ARP) service of the TCP/IP protocol
suite. It lets the network admin view the ARP cache and add or delete cache entries. It can be used to
address problems having to do with specific connections between a workstation and a host.
 dig — A Linux or UNIX command-line tool that will display name server information. It can be used to
troubleshoot problems in DNS name resolution.

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Network troubleshooting applications
In addition to command-line tools, there are also a number of standalone applications that can be used to
determine the status of a network and to troubleshoot issues. Some of these applications may be included in
the system that you are working with, while others may need to be installed separately.

 Packet sniffer — Provides a comprehensive view of a given network. You can use this application to
analyze traffic on the network, figure out which ports are open and identify network vulnerabilities.
 Port scanner — Looks for open ports on the target device and gathers information, including whether
the port is open or closed, what services are running on a given port and information about the operating
system on that machine. This application can be used to figure out which ports are in use and identify
points in a network that could be vulnerable to outside attacks.
 Protocol analyzer — Integrates diagnostic and reporting capabilities to provide a comprehensive view
of an organization's network. You can use analyzers to troubleshoot network problems and detect
intrusions into your network.
 Wi-Fi analyzer — Detects devices and points of interference in a Wi-Fi signal. This tool can help you
to troubleshoot issues in network connectivity over a wireless network.
 Bandwidth speed tester — Tests the bandwidth and latency of a user’s internet connection. This
application is typically accessed through a third-party website and can be used to confirm user reports
about slow connections or download speeds.

Hardware tools
Command-line tools and applications are software tools for troubleshooting, but some network problems
have hardware causes and solutions. Here are some hardware tools that can help you diagnose and solve
network issues:
 Wire crimpers — A wire crimper (sometimes called a cable crimper) is a tool that attaches media
connectors to the ends of cables. You can use it to make or modify network cables.
 Cable testers — A cable tester (sometimes called a line tester) is a tool that verifies if a signal is
transmitted by a given cable. You can use one to find out whether the cables in your network are
functioning properly when diagnosing connectivity issues.
 Punch down tool — A punch down tool is used in a wiring closet to connect cable wires directly to a
patch panel or punch-down block. This tool makes it easier to connect wires than it would be to do it by
hand.
 TDR — A time-domain reflectometer (TDR) is a measuring tool that transmits an electrical pulse on a
cable and measures the reflected signal. In a functioning cable, the signal does not reflect and is
absorbed in the other end. An optical time-domain reflectometer (OTDR) is a similar tool, but used for
measuring fiber optic cables, which are becoming more common in modern networks.

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 Light meter — Light meters, also known as optical power meters, are devices used to measure the
power in an optical signal.
 Tone generator — A tone generator is a device that sends an electrical signal through one pair of UTP
wires. On the other end, a tone locator or tone probe is a device that emits an audible tone when it
detects a signal in a pair of wires. You can use these tools to verify that signals are passing through the
wires in your network. They are often used to confirm phone connectivity.
 Loopback adapter — A loopback adapter is a virtual or physical tool that can be used for
troubleshooting network transmission issues. It can be used by utilizing a special connector that redirects
the electrical signal back to the transmitting system.
 Multimeter — A multimeter (sometimes called a volt/ohm meter) is an electronic measuring instrument
that takes electrical measurements such as voltage, current and resistance. There are hand-held
multimeters for fieldwork as well as bench-top models for in-house troubleshooting.
 Spectrum analyzer — A spectrum analyzer is an instrument that displays the variation of a signal
strength against the frequency.

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