1. Network Troubleshooting
Lesson 12

2. Objectives Exam Objective Matrix Technology Skill Covered
Exam Objective Number
One Size Does Not Fit All
Stages of the Troubleshooting Process
Given a scenario, implement the following network troubleshooting methodology:
Identify the problem:
Information gathering
Identify symptoms
Question users
Determine if anything has changed
Establish a theory of probable cause
Question the obvious
Test the theory to determine cause:
Once theory is confirmed determine next steps to resolve problem.
If theory is not confirmed, re-establish new theory or escalate.
Establish a plan of action to resolve the problem and identify potential effects
Implement the solution or escalate as necessary
Verify full system functionality and if applicable implement preventative measures
Document findings, actions and outcomes
1.8

3. Objectives Exam Objective Matrix Technology Skill Covered
Exam Objective Number
Network Tools and What They Are Used For
Given a scenario, use appropriate hardware tools to troubleshoot connectivity issues.
Cable tester
Cable certifier
Crimper
Butt set
Toner probe
Punch down tool
Protocol analyzer
TDR
OTDR
Multimeter
Environmental monitor
4.2

4. Objectives Exam Objective Matrix Technology Skill Covered
Exam Objective Number
Given a scenario, use appropriate software tools to troubleshoot connectivity issues.
Protocol analyzer
Throughput testers
Connectivity software
Ping
Tracert/traceroute
Dig
Ipconfig/ifconfig
Nslookup
Arp
Nbstat
Netstat
Route
4.3
Troubleshooting Actions
Given a scenario, troubleshoot common router and switch problems.
Bad cables/improper cable types
Mismatched MTU/MUT black hole
Power failure
Bad modules (SFPs, GBICs)
Given a scenario, use appropriate hardware tools to troubleshoot connectivity issues.
Loop back plug
2.5
4.2

5. Objectives Exam Objective Matrix Technology Skill Covered
Exam Objective Number
Common Connectivity Issues
Given a scenario, install and configure routers and switches.
Interface configurations
Full duplex
Half duplex
Port speeds
IP addressing
Given a scenario, troubleshoot common wireless problems.
Interference
Signal strength
Configurations
Incompatibilities
Incorrect channel
Latency
Encryption type
Bounce
SSID mismatch
Incorrect switch placement
2.1
2.4

6. Objectives Exam Objective Matrix Technology Skill Covered
Exam Objective Number
Given a scenario, troubleshoot common router and switch problems.
Switching loop
Bad cables/improper cable types
Port configuration
VLAN assignment
Bad/missing routes
Wrong subnet mask
Wrong gateway
Duplicate IP address
Wrong DNS
2.5
Given a scenario, troubleshoot common physical connectivity problems.
Cable problems:
Bad connectors
Bad wiring
Open short
Split cables
DB loss
TXRX reversed
Cable placement
EMI/Interference
Distance
Cross-talk
3.6

7. One Size Does Not Fit All
Computers and networks are different
Knowing how to fix one computer or one network does not necessarily mean you know how to fix them all
Troubleshooting requires:
Knowledge
Intuition
Experience

8. Stages of the Troubleshooting Process
Identify Problems
Identify Affected Areas of Network
Determine Changes Made
Establish Probable Cause
Escalate?
Create Action Plan
Implement and Test Solution
Identify Results
Document Solution
Information gathering—Identify the systems and the problems
Identify the affected areas of the network
Determine whether anything has changed
Establish the most probable cause
Determine if escalation is necessary
Create an action plan and solution
Identify potential effects
Implement and test the solution
Identify the results and effects of the solution
Document the solution and the entire process
Document problem reporting
Document the troubleshooting process
Document the solution

9. Bringing the Steps of the Troubleshooting Process Together
Discussion: How would you go about bringing the steps of the troubleshooting process together?
An end user suddenly loses connectivity to the corporate network. She reports the problem to tech support. Tech support assigns you to resolve the issue.
Instructor: This is the example explored in Lesson 9. Feel free to change the example for the discussion.

10. Network Tools and What They Are Used For
Command-line interface (CLI) network tools
Hardware tools

11. CLI Tools and Their Platforms
Ipconfig
DOS/Windows
Ifconfig
Linux/UNIX
Ping
DOS/Windows & Linux/UNIX
Traceroute
Tracert
My traceroute (MTR)
Pathping
Arping
Arp
NSlookup
Hostname
Domain Information Groper (Dig)
Route
Nbtstat
Netstat

12. Ipconfig
A command-line tool found in all current versions of Microsoft Windows
Displays the IP address, subnet mask, and default gateway of each adapter on which the computer is run

13. Ipconfig Command

14. Ipconfig /all Command

15. Ifconfig
Ifconfig = Interface Configuration
Linux/UNIX equivalent to ipconfig
Without parameters, ifconfig returns same information as ipconfig
However, ifconfig has many more parameters than ipconfig

16. Ifconfig Command (Linux/UNIX)

17. Man ifconfig Command (Linux/UNIX)
To learn about command-line commands and tools in DOS/Windows use the /? parameter.
To learn about command-line commands and tools in Linux/UNIX use the man command.

18. Test network; determine where connectivity is lost
Ping
Determines if a specific IP address is reachable on the network
Ping an IP address
Test network; determine where connectivity is lost
Ping is used the same way in both Linux/UNIX and DOS/Windows environments.

19. Ping Command (DOS/Windows)

20. Ping Command (Linux/UNIX)

21. Traceroute and Tracert
Linux/UNIX CLI tool that reports each stop a packet makes on way to a destination
IP address identifies the destination for which you wish to find the route to
Tracert
DOS/Windows equivalent to traceroute
Works the same as traceroute, uses fewer parameters

22. Traceroute (Linux/UNIX) and Tracert (Windows)

23. My Traceroute (MTR)
Linux/UNIX command-line tool that combines the capabilities and functionality of traceroute and ping

24. Pathping
Similar to the Linux mtr tool
Combines functionality of the ping and tracert commands

25. ARP Ping
A ping command using the ARP protocol to issue an “arp request” rather than the ICMP protocol to issue an “echo request”
Can only be performed in Linux/UNIX
Command to do an ARP ping is arping

26. Pathping yahoo.com –q 10

27. Displays arp table of a computer
Arp table is kept by all network devices; contains the IP address and MAC address of all the other network devices with which it has been in contact
Aside from displaying arp tables, arp can also be used to manipulate arp tables by adding or removing MAC addresses.
Hackers sometimes use this last functionality for quite a few nefarious purposes

28. Nslookup
Looks up DNS servers; displays servers for a particular domain
Displays the IP address of the DNS server on the network being used to run nslookup

29. Hostname
Displays or changes the DNS hostname of the local machine
Output in UNIX/Linux and DOS/Windows environments is almost identical

30. Domain Information Groper (dig)
Queries DNS servers to gain information about them
Similar to nslookup, but dig can provide more detailed information
Only available in Linux/UNIX environments

31. Dig Tool (Linux/UNIX)

32. Route
Used to view and/or manipulate the routing table located on the targeted device, either by adding or removing static routes
Sets up static routes to specific network locations from the local interface
Works the same way in both the Linux/UNIX and DOS/Windows environments

33. Route (DOS/Windows)

34. Nbtstat
Obtains information about a local machine and the devices it is connected to, based on NetBIOS names
Novell and Windows no longer use NetBIOS names for creating network IDs, so nbtstat is no longer in common usage

35. Nbtstat (DOS/Windows)

36. Netstat
Displays information about network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
Works in both the Linux/UNIX and the DOS/Windows environment

37. Netstat (Linux/UNIX) Showing Active Protocols and Sockets on Local Computer

38. Netstat (DOS/Windows) Showing Open TCP Ports on Local Computer

39. Connectivity Software
Programs that connect computers or other types of electronic devices to another computer or a network
Is usually specifically designed for the device it is being used to connect and is hardware dependent
Usually comes with a test component

40. Hardware Tools
Tools that physically exist as opposed software programs
Several types of hardware tools are available for troubleshooting and fixing a network

41. Cable Tester
Tests the connectivity of various cables as well as any subcomponents within them
Can test all pairs in a twisted-pair wire

42. Cable Tester Designed to Test a Large Variety of Cable Wires

43. Software-based or hardware-based
Protocol Analyzers
Software-based or hardware-based
Both capture and analyze network packets
Both test a network with a specific protocol
Hardware-based
Entirely self-contained system with software
Connect to a data jack
Tests if different network segments meet the specifications needed to run different types of data networks

44. Certifiers
Devices used to certify that the cables in a network configuration meet the required physical specification
Some of the things that certifiers can verify are the physical properties of the cable, the signal carrying properties of a cable, the length of a cable,
where connections are made within a system, and many other physical properties.

45. Time-Domain Reflectometers (TDRs)
Tests in-place cables
When connected to a metal cable, sends an electrical pulse down the wire
Response may indicate a fault in the wiring and where fault is located
TDRs can also be used in metal circuit boards and can tell where faults may be in the circuit board.

46. Optical Time-Domain Reflectometer (OTDR)
Basically a TDR for fiber-optic cables
Works the same way as a TDR but designed for fiber-optic cable instead of copper cables

47. A device designed to take several types of measurements
Multimeter
A device designed to take several types of measurements
Most multi- meters measure voltage, amperage, resistance, and continuity
Many multimeters also able to test other types of measurements such as temperature
Can troubleshoot the power supply in a network device

48. Throughput Testers
Devices or software programs that test how fast data is passes through a network connection
Hardware throughput testers used when network wiring is first run in a site where network wiring is being run
Software throughput testers are more often used after a network is in place

49. A tool that finds the end of a long run of a specific cable
Toner Probe
A tool that finds the end of a long run of a specific cable
Works with a tone generator
A tone generator is connected to one end of the long run and turned on.
The technician then goes into the switch room where the various cable runs terminate and waves the wand of the toner probe over the different terminations until she is able to pick up the tone that is generated by the tone generator.
This lets the technician know that the cable she is picking up the tone on is the termination point in the switch or patch panel for the cable she is trying to
find the end of.

50. Butt Set
Also called “lineman phones”
Devices used in telephone communications
Technician connects the butt set to any phone connection and uses that connection like a regular phone, or tests the connection to make sure it is working
Butt sets often look like miniature phone handsets with alligator clips hanging off them

51. Terminates wires on a 110 block or 66 block
Punch Down Tool
Terminates wires on a 110 block or 66 block
110/66: Connections that are generally found on the back of patch panels where the cables going out to the wall jacks are connected
Can terminate wires into an RJ-45 jack as well

52. Cable Strippers
Strip the insulation off of a cable for various purposes
Shape and size dependent on type of cable it is designed to strip

53. Telecommunications scissors
Snips or Wire Cutters
Telecommunications scissors
Handheld devices that cut wire, wire ties, and similar items
Can serve as a cable stripper

54. Crimper
A device used to attach connectors to the end of a cable
May be designed for a specific cable or connector type
Some crimpers have multiple removable dies, can use on many cable and connector types

55. Voltage Event Recorder
A device that monitors electrical circuits and looks for problems in the electricity coming though a circuit
Can detect and report different electrical conditions
Power sags, power swells, transient power events, outages, and spikes or other variations in the power system

56. Environmental Monitors
Devices used to monitor the area in a building where sensitive equipment is located
Temperature monitors
Humidity monitors

57. Basic Troubleshooting Actions
Check for physical problems
Perform loopback testing
Perform ping tests
Perform trace route tests

58. Advanced Troubleshooting Actions
Cable testing
Use cable tester
May detect wrong cable type or bad cable
Protocol analysis
May help detect suspicious network activity
Time-Domain Reflectometer (TDR)
Tests network cable runs to verify that there are no breaks

59. Advanced Troubleshooting Actions (Cont.)
Switch and router configuration testing
Mismatched MTU
MTU black hole
Bad modules
Small form factor pluggable (SFPs)
Gigabit interface controller (GBIC)
Power failure

60. Common Connectivity Issues
Physical issues
Logical issues
Wireless issues

61. Physical Issues Bad connectors Bad wiring Split cables TXRX reversed
Cable placement

62. Physical Issues (Continued)
Crosstalk
Attenuation
Collisions
Shorts
Open impedance mismatch (echo)
Interference

63. Logical Issues
Incorrect IP address
Incorrect VLAN
Wrong subnet mask
Wrong gateway
Wrong DNS address
Port configuration issues
Port speed
Port duplex mismatch

64. Speed & Duplex Options in a NIC’s Properties Dialog Box

65. Issues That Should Be Escalated
Switch loop
Multiple switches keep sending frames back and forth to each other and nowhere else
Routing loop
Routers keep sending packets back and forth to each other and nowhere else
Route problems
Problems with the router’s routing table

66. Issues That Should Be Escalated (Continued)
Proxy ARP
Takes an ARP query from one place on the network and forwards it to another place on the network using its own MAC address instead of the MAC address of the device making the query
Broadcast storms
Caused when packets keep getting broadcasted from one network device to another

67. Wireless Issues Interference
Caused by strong electromagnetic fields that interfere with the electric impulses used to send signal across a copper wire
Wireless networks involve interference with radio frequency (RF) waves
Types of interference:
Bleed
Environmental factors

68. Wireless Networks with Overlapping Ranges but Not Overlapping Channels

69. Wireless Issues (Continued)
Incorrect channel
A network device set to the wrong channel cannot access the intended network
Will access a different network or no network at all
Incorrect encryption
Occurs when device uses a different encryption algorithm (such as WEP) than a wireless access point (such as WPA2)

70. Wireless Issues (Continued)
Incorrect frequency
Occurs if you use customized frequency ranges for each channel, and then not set all the channels used on the wireless network to the same frequency ranges
ESSID mismatch
A wireless device on the network with an incorrect ESSID configured (ESSID mismatch) cannot communicate with the wireless access point

71. Wireless Issues (Continued)
Standards mismatch ( A/B/G/N)
Device (Standard)
Compatibility N
Can read all the other devices G
Can read G and B devices A
Can only read themselves, and can be read by N devices. B
Can only read other B devices, and can be read by G or N devices.

72. Wireless Issues (Continued)
Distance
Latency
Bounce
Certain surfaces and materials can reflect and split radio signals
Bouncing of wireless signals can limit the range of a wireless network

73. Wireless Issues (Continued)
Incorrect switch placement
Wireless switch should be centrally located with respect to devices
Away from EMI
Incorrect antenna placement
The further an antenna is away from the wireless device it is serving, the more disrupted the signal will be because it has to follow a longer wire

74. Summary
Troubleshooting network problems requires knowledge, intuition, and experience.
Troubleshooting involves many different stages.
Network troubleshooting tools include command-line-interface tools and hardware tools.
Basic troubleshooting actions include:
Check for physical problems
Perform loopback testing
Perform ping tests
Perform trace route tests

75. Summary (Continued)
Advanced troubleshooting actions range from cable testing to protocol analysis to switch and router configuration testing.
Network connectivity problems are physical or logical in nature, or related to wireless issues.