CompTIA exam study guide presentations by instructor Brian Ferrill, PACE-IT (Progressive, Accelerated Certifications for Employment in Information Technology) "Funded by the Department of Labor, Employment and Training Administration, Grant #TC-23745-12-60-A-53" Learn more about the PACE-IT Online program: www.edcc.edu/pace-it

1. Troubleshooting
common network
issues.

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Instructor, PACE-IT Program – Edmonds Community College
Areas of expertise Industry Certifications
 PC Hardware
 Network Administration
 IT Project Management
 Network Design
 User Training
 IT Troubleshooting
Qualifications Summary
Education
 M.B.A., IT Management, Western Governor’s University
 B.S., IT Security, Western Governor’s University
Entrepreneur, executive leader, and proven manger
with 10+ years of experience turning complex issues
into efficient and effective solutions.
Strengths include developing and mentoring diverse
workforces, improving processes, analyzing
business needs and creating the solutions
required— with a focus on technology.

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PACE-IT.
– Problems to escalate.
– Problems to resolve.

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Troubleshooting common network issues.

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The complexity of modern
networking has made using
a solid troubleshooting
methodology a necessity.
Networks can express problems and issues in many ways.
This can lead to much frustration on the part of network
users and the technicians responsible for fixing problems. If
such problems are not resolved quickly, they can lead to
loss of revenue and productivity for an organization.
There are a number of problems that should be escalated
up the troubleshooting chain in order for them to be resolved
in the most expedient manner.
Troubleshooting common network issues.

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Troubleshooting common network issues.
– Switching loop.
» Users complain that the network works fine for a while, then
goes down, and then works fine for a while.
• This indicates an STP (Spanning Tree Protocol) convergence
issue.
– Broadcast storm.
» A failing NIC or application may cause a situation in which a
broadcast storm is created.
• The NIC goes down and then comes back up repeatedly—
referred to as a flapping NIC. Each time it comes up, it sends
out a broadcast advertising its status, which creates traffic
congestion.
– Routing loop.
» Similar in nature to the switching loop, but involves the routing
process. This is more likely to occur with older routing protocols
(e.g., RIP v.2) but may also occur due to a misconfiguration of
routers (e.g., multiple static routes to the same location).
• Often, switching to a newer routing protocol (e.g., OSPF) will
resolve or banish routing loops.

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Troubleshooting common network issues.
– Other routing problems.
» Routing problems can manifest themselves in many different
ways including:
• Missing IP routes.
• Failure to discover neighboring devices.
• Failure to connect to neighboring devices.
» When routing problems are suspected, it is necessary to
escalate the issue to the proper technical team.
– Mismatched maximum transmission unit
(MTU) or the MTU black hole.
» Different types of WAN connections have different MTU
settings—the largest allowable size of a packet that can
traverse the link or be accepted by the link.
• Routers will negotiate the MTU between links using ICMP
(Internet Control Message Protocol).
» If ICMP has been disabled on the routers—a common
practice—when a router receives a packet that exceeds the
MTU, it will not respond and will drop the packet.
• The sending router continues to send the oversized packets
into the MTU black hole.

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Troubleshooting common network issues.
– NIC teaming.
» The process of bonding multiple NICs on a single system for
the purposes of increasing bandwidth, or for failover purposes.
• A misconfiguration may actually cause a loss of performance
or, in a worse case scenario, the total loss of functionality.
– Power failure or power anomalies.
» Power failures are easy to diagnose, but may be difficult to
recover from. While battery backups and generators may
mitigate the issue, they will not resolve the problem.
• If the problem occurs within the building, contact the
appropriate group responsible for building maintenance.
• If the problem occurs outside the building, contact the
appropriate utility.
» Electronic devices are sensitive to power issues. Anomalies in
the quality of the electricity delivered to a device may cause
problems.
• Using battery backups combined with power conditioners will
help to mitigate power anomalies.

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Troubleshooting common network issues.

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Troubleshooting common network issues.
– Incorrect IP configuration.
» Default gateway: local network’s or computer’s access to the
outside. An incorrect gateway will keep traffic from reaching its
destination.
• Verify the correct gateway settings and correct.
» Duplicate IP address: when duplicate IP addresses have been
configured, the first device booted up will get the address and the
second one up will get an address supplied by APIPA (Automatic
Private IP Addressing).
• Can occur when DHCP address reservation has not been
configured correctly.
• Verify and correct the configuration.
» DHCP misconfiguration: the problem is expressed in a similar
manner as the duplicate IP address problem (e.g., an APIPA
address is supplied) and is caused by a misconfiguration of DHCP.
• Verify DHCP settings and correct.
» DNS misconfiguration: users complain that they cannot get to
resources or destinations on the network when using the hostname.
DNS resolves hostnames to IP addresses, so a misconfiguration
will prevent the function of the process.
• Verify the correct DNS settings and correct.

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Troubleshooting common network issues.
– Incorrect VLAN assignment.
» Users complain that they cannot get to necessary network
resources.
• Tends to be a single host issue or involve a small group of
hosts.
• Verify VLAN settings and correct as necessary.
– Incorrect interface configuration.
» Users complain of poor network performance, or not being able
to connect to resources at all.
• Tends to affect a whole network segment.
• Configuration issues could include: mismatched port speeds
and/or duplex settings on the interfaces.
• Verify the correct interface configurations and correct the
settings.

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Troubleshooting common network issues.
– Simultaneous wireless and wired connection.
» Many laptops come with wireless and wired network capabilities
built into them. It is possible (though not very probable) for a
laptop to attempt to use both at the same time. This may cause
the device to quit communicating on the network.
• Reminding users to turn off wireless capabilities before joining
the wired network will resolve the problem.
– End-to-end connectivity.
» The complexity of networks will just about guarantee that end-to-
end connectivity—the ability to reach remote hosts—will be lost
at some point.
• The ping and tracert/traceroute utilities can be used to find
where the break in communication occurs. This information can
be used to determine the next course of action.
– Hardware failure.
» Networking equipment and devices will fail. When this happens,
it is usually denoted by the sudden loss or intermittent loss—in
the case of failing equipment—of function or access.
• Determining what failed and replacing it is the solution.

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Troubleshooting common network issues.
Using a methodology will ease the troubleshooting process. As part of that
methodology, knowing when to escalate the issue up the troubleshooting
chain is important. Some problems that should be escalated include:
switching loops, broadcast storms, routing loops, other routing problems, an
MTU black hole, NIC teaming configuration issues, and power problems.
Topic
Problems to escalate.
Summary
While there are networking problems that should be escalated, there are
others that can be easily resolved. These include: incorrect IP configuration,
VLAN assignment, and interface configurations; simultaneous wireless and
wired network connections; end-to-end connectivity issues; and hardware
failures.
Problems to resolve.

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THANK YOU!

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