Network Troubleshooting, Domain 5

Gather information

Collect data related to the issue, such as error messages, affected systems, and recent changes.

Question users

Interview individuals experiencing the problem to gain insights into the issue.

Identify symptoms

Recognize signs or indications of the problem affecting the network.

Determine if anything has changed

Investigate recent modifications or updates that may have led to the issue.

Duplicate the problem, if possible

Replicate the problem to understand its causes better.

Approach multiple problems individually

Address each network issue separately to avoid confusion.

Question the obvious

Challenge assumptions and consider less apparent causes of the problem.

Top-to-bottom/bottom-to-top OSI model

Troubleshoot network layers systematically, starting from the top or bottom of the OSI model.

Divide and conquer

Break down the issue into smaller parts to isolate the root cause.

Throughput

The amount of data that can be transferred in a specific amount of time, often measured in bits per second.

Speed

The rate at which data is transmitted through a network, typically expressed in megabits or gigabits per second.

Distance

The maximum length that a signal can travel over a network medium before experiencing signal degradation.

Shielded and unshielded

Different types of cables with shielding to protect against electromagnetic interference.

Plenum and riser-rated

Cable types designed for different installation environments, with plenum cables suitable for air handling spaces and riser-rated cables for vertical runs between floors.

Rollover cable/console cable

Used to connect a computer's serial port to the console port of networking devices for configuration.

Crossover cable

Directly connects similar devices for data transfer without an intermediary network device.

Power over Ethernet

Technology that allows electrical power to be transmitted over Ethernet cables to power network devices.

Attenuation

Loss of signal strength as it travels through a medium.

Interference

External signals disrupting the normal transmission of data.

Decibel (dB) loss

Measurement of signal strength reduction in a cable or network component.

Incorrect pinout

Misconfiguration of cable wiring affecting connectivity.

Bad ports

Faulty or damaged ports on networking devices.

Open/short

Issues in cables where there is either a break in the connection (open) or a direct connection (short).

Light-emitting diode (LED) status indicators

Lights on networking equipment indicating operational status.

Incorrect transceivers

Incompatible or faulty transceivers affecting data transmission.

Duplexing issues

Problems with simultaneous two-way data transmission.

Transmit and receive (TX/RX) reversed

Swapped connections causing transmission errors.

Dirty optical cables

Contaminated fiber optic cables affecting signal quality.

Cable crimper

Tool for attaching connectors to the ends of network cables.

Punchdown tool

Used to terminate network cables into patch panels or keystone jacks.

Tone generator

Device for tracing and identifying cables.

Loopback adapter

Diagnostic tool to test network ports.

Optical time-domain reflectometer (OTDR)

Equipment to analyze the characteristics of optical fibers.

Multimeter

Tool for measuring voltage, current, and resistance in electrical circuits.

Cable tester

Device to verify the integrity of network cables.

Wire map

Tool for identifying how wires are connected in a network cable.

Tap

Device for monitoring network traffic.

Fusion splicers

Equipment for joining optical fibers together.

Spectrum analyzers

Instruments for analyzing signal frequency and strength.

Snips/cutters

Tools for cutting and stripping cables.

Cable stripper

Tool for removing the protective covering from cables.

Fiber light meter

Device for measuring the power of light transmitted through fiber optic cables.

WiFi analyzer

Software used to analyze wireless networks, including signal strength, channels, and interference.

Protocol analyzer/packet capture

Tools that capture and analyze network traffic for troubleshooting and monitoring.

Bandwidth speed tester

Applications that measure the speed and quality of an internet connection.

Port scanner

Software used to scan a network for open ports on target machines.

iperf

Tool for measuring network performance by generating TCP and UDP data streams.

NetFlow analyzers

Tools that collect and analyze NetFlow data to monitor network traffic.

Trivial File Transfer Protocol (TFTP) server

Software that allows for file transfers over a network, often used for network device configuration.

Terminal emulator

Program that emulates a terminal to access a command-line interface on a remote device.

IP scanner

Software for scanning a range of IP addresses to identify active hosts on a network.

ping

Utility to test the reachability of a host on a network.

ipconfig/ifconfig/ip

Commands to display or configure network interface information.

nslookup/dig

Tools for querying DNS servers to retrieve domain name information.

traceroute/tracert

Commands for tracing the route packets take to reach a destination.

arp

Command to view and manipulate the Address Resolution Protocol (ARP) cache.

netstat

Command to display network connections, routing tables, and interface statistics.

hostname

Command to view or set the hostname of a device.

route

Command to view or manipulate the IP routing table.

telnet

Program to establish a command-line connection to a remote device.

tcpdump

Command-line packet analyzer for network troubleshooting.

nmap

Tool for network exploration and security auditing.

show interface

Command to display information about network interfaces.

show config

Command to view device configuration settings.

show route

Command to show the routing table and routing information on a device.

Throughput

The amount of data that can be transferred through a network in a given time.

Speed

The rate at which data is transmitted and received in a wireless network.

Distance

The range over which wireless signals can effectively transmit data.

Received signal strength indication (RSSI)

Measurement of the power level of the signal received by a wireless device.

Effective isotropic radiated power (EIRP)/power settings

Measure of the power radiated from an antenna in a specific direction.

Placement

Positioning of antennas to optimize signal coverage and strength.

Type

Different antenna designs suited for specific purposes or coverage areas.

Polarization

Alignment of antenna polarization for improved signal reception.

Channel utilization

Efficient allocation and usage of wireless channels to minimize interference.

AP association time

Duration taken for wireless devices to connect to an access point.

Site survey

Assessment of a location to determine optimal wireless network deployment.

Channel overlap

When multiple wireless networks use the same channel, causing interference.

Antenna cable attenuation/signal loss

Reduction in signal strength due to the length and quality of antenna cables.

RF attenuation/signal loss

Weakening of radio frequency signals over distance or obstacles.

Wrong SSID

Connection issues due to attempting to connect to the wrong wireless network.

Incorrect passphrase

Authentication failure due to entering an incorrect network password.

Encryption protocol mismatch

Incompatibility between encryption settings on devices causing connectivity problems.

Insufficient wireless coverage

Areas with weak or no wireless signal coverage.

Captive portal issues

Problems accessing network resources due to captive portal authentication challenges.

Client disassociation issues

Devices disconnecting from the network unexpectedly, impacting connectivity.

Device configuration review

Examination of device settings and parameters for troubleshooting purposes.

Routing tables

Data tables used by routers to determine the best path for forwarding network traffic.

Interface status

Information about the operational state of network interfaces.

VLAN assignment

Grouping devices into virtual LANs for network segmentation and management.

Network performance baselines

Establishing benchmarks for network performance to identify deviations.

Collisions

When two devices attempt to transmit data simultaneously, leading to signal interference.

Broadcast storm

Excessive broadcast or multicast traffic overwhelming network resources.

Duplicate MAC address

Two devices sharing the same MAC address causing network conflicts.

Duplicate IP address

Two devices assigned the same IP address, disrupting network communication.

Multicast flooding

Uncontrolled forwarding of multicast traffic to all network devices.

Asymmetrical routing

Network traffic taking different paths to reach the same destination, causing issues.

Switching loops

Circuits in a network that create broadcast storms and disrupt connectivity.

Routing loops

Redundant paths in routing tables causing packets to loop indefinitely.

Rogue DHCP server

Unauthorized DHCP server providing incorrect network configurations.

DHCP scope exhaustion

Depletion of available IP addresses in the DHCP address pool.