Testing and troubleshooting networks

Testing and Troubleshooting
Networks

Network troubleshooting Tools
• The various tools available for checking the network are:
– Software Tools
– Hardware Tools
– Touchy Tools

Loopback Test
• Signal is transmitted and it echos back
• Echo signal compared with original signal
• Tests the transmission path and tools used for
transmission
• Traces a faulty node in network
• Requires a loopback plug

Chapter 4 3

Network Monitors

• Detect and display problems present in the network

• Provides data related to network traffic

• Analyze data traffic to determine various network
problems that can occur

LAN Tester - I

• Used to test 10, 100 and 1000 Base-
T Networks
• Consists of two units
– Main unit
• Indicates LAN device type i.e hub,
switch
• Determines speed of LAN and type of
link
– Remote Probe
• Used to locate faults in a cable

Chapter 4 5

LAN Tester - II
• Functions of LAN tester
– Verify PC to hub speed and data transmission
– Check hub to hub data transmission
– Determines any speed bottlenecks present on 10 and 100
Base-T LANs
– Continuously tracks LAN link

Cable Testers and Certifiers
• Checks electrical connections
• Determines if a short or open
circuit is present in the network
• Consists of a source of current,
volt meter and microcontroller

Time-Domain Reflectometers
• Locates fault in metallic cables
• Transmits a pulse through the cable
• At every discontinuity, an echo is
reflected back
• Used to test long cables
• Results are displayed on a CRT or LCD

Protocol Analyzers - I
• It may be a software or hardware device
• Captures packets from network
• Analyzes captured packets
• Analyzes the network traffic
• Identifies bottlenecks in network
• Operate on network layer
• Identifies active systems on network
• Removes the faulty system from network

Protocol Analyzers - II
Types of protocol analyzers
– Packet analyzer
• Capture packets present on the wire and store them for
analyzing later
• Does a statistical analysis of the data captured but it is
not its primary function
– Statistical analyzers
• Gather quantitative data to prepare a report on the
different statistical trends
• Does not store the packets for later analysis

Touchy Tools
• Used to identify network problems
• Problems are identified using asking various questions to
user
• Analyzes current situation and compares it with set of
baselines
• Adequate knowledge and experience is useful to
determine problems

Backups
• Used to preserves a copy of original files
• Should be performed on regular basis
• Useful when a data loss occurs
• Restores system to previous state

Baselines
• Used to compare the system’s current performance with
reference level set by the network administrator
• Determines possible network problems
• Performance monitor helps to set baselines
• Monitors both real time as well as historical data
• Baselines may change with time

Troubleshooting Model - I
• Steps of troubleshooting model
– Establish the symptoms
– Isolate the cause of the problem
– Establish what has changed that might have caused the
problem
– Ask Isolating questions

Troubleshooting Model - II

– Identify the most probable cause
– Implement a solution
– Test the solution
– Recognize the potential effects of the solution
– Document the solution

Four layer Model
• Four layers model
– Hardware – Considers all the hardware related issues
• Focuses on problems with network devices such as hubs,
switches
– Protocols – Deals with problems related to protocols
• Checks the installation and configuration of protocols
– Network – Considers the client and server concept
• Determines which node will act as client and which will
act as server
– Shared Resources – Determines which resources are to be
shared

Cable Testing and Certification - I
• Cable Distance
– Measures the distance of a cable and helps to locate the
point where a short or open is present
– Speed of pulse depends on wires, type of insulation and
external shielding
• Wire Map
– Used for twisted-pair
installations
– Detects split pairs
– Detects crossed pair condition

Cable Testing and Certification - II
• Attenuation
– Reduction in strength of signal
– Cable Testers are used to measures loss of power
• Near-End Crosstalk
– Transfer of electricity from one wire to another in the
same cable
– Causes
• Untwisted patch cables
• Crossed pairs

Cable Testing and Certification - III
• Network Monitoring and Protocol Decoding
– Cable checkers monitor network traffic
• Detects high or low level traffic
– Locates loose cables
• Noise-Level Test
– External signal that interfere with original signals
– Measured in millivolts (mV)
• Testing Fiber
– Fiber-optic cable testers use optical time-domain
reflectometer which depend on the reflection of light

SNMP
• Simple Network Management Protocol
• Networking standard protocol
• Used with TCP/IP networks
• Monitors and manages the network
• Helps to examine network performance
• Detect network faults or inappropriate access

Potential Network connectivity
problem
• Causes of network connectivity problems
– Incorrect network adapters (NIC)
– Incorrect switch settings
– Faulty hardware
– Driver issues
– Upgradation of operating system
– Server relocation
– The network adapter is incompatible with the motherboard

Network Workstation Troubleshooting
Process
• Steps to troubleshoot network workstation
– Determine what stopped working
– Determine if failure is on a single user’s workstation
– Try to log onto the network
– Check the NIC’s link light

Netstat Command
• Displays TCP/IP information
• Determines which ports are active
• Identifies ports that are vulnerable to attacks
• Provides connection details
• Provides data about TCP and UDP

Ipconfig Command
• Displays all network settings
• Identifies DHCP problems
• Used with windows 2000 and later versions
• Displays and resets DNS cache
• Sets and displays DHCP class IDs for an adapter

Winipcfg Command
• Provides IP addressing details
• Used for windows 98 or earlier versions
• Provides details such as IP address, Subnet Mask, Default
Gateway, DHCP Server, WINS Server, etc.

ARP Command
• Links IP address of a node with its hardware address
• Various ARP command options can be used to display or
change the values in ARP table

Nbtstat Command
• Resolves NetBIOS name resolution problems
• Used when WINS server is not accessible
• displays protocol information and current TCP/IP
connection using NetBIOS over TCP/IP (NBT)

Route Command
• Allows you to view and make changes in the IP routing
table
• Used to differentiate between routes to hosts and routes
to networks by reading the network address of the
destination

Testing and troubleshooting networks

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