Transcript Device

Network Troubleshooting
Lesson 12
Objectives
Exam Objective Matrix
Technology Skill Covered
Exam Objective
Exam Objective Number
One Size Does Not Fit All
Stages of the Troubleshooting Process
Given a scenario, implement the following
1.8
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
Objectives
Exam Objective Matrix
Technology Skill Covered
Exam Objective
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
Objectives
Exam Objective Matrix
Technology Skill Covered
Troubleshooting Actions
Exam Objective
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
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
4.3
2.5
4.2
Objectives
Exam Objective Matrix
Technology Skill Covered
Exam Objective
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
2.1
Given a scenario, troubleshoot common wireless
problems.
• Interference
• Signal strength
• Configurations
• Incompatibilities
• Incorrect channel
• Latency
• Encryption type
• Bounce
• SSID mismatch
• Incorrect switch placement
2.4
Objectives
Exam Objective Matrix
Technology Skill Covered
Exam Objective
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
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
2.5
3.6
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
Stages of the Troubleshooting Process
Identify
Affected Areas
of Network
Determine
Changes
Made
Establish
Probable
Cause
Escalate?
Create Action
Plan
Implement
and Test
Solution
Identify
Results
Document
Solution
Identify
Problems
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.
Network Tools and What They Are Used For
• Command-line interface (CLI) network tools
• Hardware tools
CLI Tools and Their Platforms
CLI Tool
Platform
Ipconfig
DOS/Windows
Ifconfig
Linux/UNIX
Ping
DOS/Windows & Linux/UNIX
Traceroute
Linux/UNIX
Tracert
DOS/Windows
My traceroute (MTR)
Linux/UNIX
Pathping
DOS/Windows
Arping
Linux/UNIX
Arp
DOS/Windows & Linux/UNIX
NSlookup
DOS/Windows & Linux/UNIX
Hostname
DOS/Windows & Linux/UNIX
Domain Information Groper (Dig)
Linux/UNIX
Route
DOS/Windows & Linux/UNIX
Nbtstat
DOS/Windows
Netstat
DOS/Windows & Linux/UNIX
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
Ipconfig Command
Ipconfig /all Command
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
Ifconfig Command (Linux/UNIX)
Man ifconfig Command (Linux/UNIX)
Ping
• Determines if a specific IP address is
reachable on the network
Test network;
determine where
connectivity is
lost
Ping an IP
address
Ping Command (DOS/Windows)
Ping Command (Linux/UNIX)
Traceroute and Tracert
• Traceroute
– 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
Traceroute (Linux/UNIX) and Tracert
(Windows)
My Traceroute (MTR)
• Linux/UNIX command-line tool that
combines the capabilities and functionality
of traceroute and ping
Pathping
• Similar to the Linux mtr tool
• Combines functionality of the ping and
tracert commands
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
Pathping yahoo.com –q 10
ARP
• 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
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
Hostname
• Displays or changes the DNS hostname of
the local machine
• Output in UNIX/Linux and DOS/Windows
environments is almost identical
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
Dig Tool (Linux/UNIX)
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
Route (DOS/Windows)
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
Nbtstat (DOS/Windows)
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
Netstat (Linux/UNIX) Showing Active Protocols
and Sockets on Local Computer
Netstat (DOS/Windows) Showing Open TCP
Ports on Local Computer
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
Hardware Tools
• Tools that physically exist as opposed
software programs
• Several types of hardware tools are available
for troubleshooting and fixing a network
Cable Tester
• Tests the connectivity of various cables as
well as any subcomponents within them
• Can test all
pairs in a
twisted-pair wire
Cable Tester Designed to Test a Large Variety
of Cable Wires
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
Certifiers
• Devices used to certify
that the cables in a
network configuration
meet the required
physical specification
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
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
Multimeter
• A device designed to take several types of
measurements
• Most multimeters measure
voltage,
amperage,
resistance,
and continuity
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
Toner Probe
• A tool that finds the end of a long run of a
specific cable
• Works with a
tone generator
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
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
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
Snips or Wire Cutters
• Telecommunications scissors
• Handheld devices that cut wire, wire ties,
and similar items
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
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
Environmental Monitors
• Devices used to monitor the area in a
building where sensitive equipment is
located
– Temperature monitors
– Humidity monitors
Basic Troubleshooting Actions
Check for
physical
problems
Perform
loopback testing
Perform ping
tests
Perform trace
route tests
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
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
Common Connectivity Issues
• Physical issues
• Logical issues
• Wireless issues
Physical Issues
Bad
connectors
Bad wiring
Split cables
TXRX
reversed
Cable
placement
Physical Issues (Continued)
Crosstalk
Attenuation
Collisions
Shorts
Open
impedance
mismatch
(echo)
Interference
Logical Issues
• Incorrect IP address
• Incorrect VLAN
• Wrong subnet mask
• Wrong gateway
• Wrong DNS address
• Port configuration issues
• Port speed
• Port duplex mismatch
Speed & Duplex Options in a NIC’s Properties
Dialog Box
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
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
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
Wireless Networks with Overlapping Ranges
but Not Overlapping Channels
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)
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
Wireless Issues (Continued)
• Standards mismatch (802.11 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.
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
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
Summary
• Troubleshooting network problems requires
knowledge, intuition, and experience.
• Troubleshooting involves many different stages.
• Network troubleshooting tools include commandline-interface tools and hardware tools.
• Basic troubleshooting actions include:
– Check for physical problems
– Perform loopback testing
– Perform ping tests
– Perform trace route tests
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.