Download Troubleshooting Your Network

Troubleshooting Your
Network
Networking for Home and Small Businesses – Chapter 9
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9.1.1 The Troubleshooting Process
 Most experienced people rely on instinct to help troubleshoot
 Important to maintain documentation to help in the process
– record problems encountered
– what steps were taken to determine the cause
– what steps have been taken to make sure it doesn’t occur again
–Document all steps even the ones that did not solve the issue
•This becomes a valuable reference in the future
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9.1.2 The Troubleshooting Process
 Step 1 – Gather information
– Question the individual who has the problem
• end user experiences
• observation by the user
• error messages
 Step 2 – Collect information about affected equipment
–Gathered from documentation
–look at logged files
– changes made to equipment configurations
– warranty information
– network monitoring tools
• used for larger networks
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9.1.3 Troubleshooting Techniques
 Use OSI layered approach
 Top-down
– start at application layer
– work down until faulty error occurs
–Is it just one application failing?
 Bottom-up
– start at physical layer and work up
–hardware failures
–Cabling connection problems (loose cable, wrong cable)
 Divide and Conquer
– begins in the middle layers
–Works up or down
–Start at network layer, verify IP config
– based on experience
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9.1.3 Approaches to Troubleshooting
 Trial and Error
– relies on an individual’s knowledge to determine most probably cause
– educated guess based on past experiences
– if it doesn’t work, try, try again until problem is solved
–Could be extremely fast
•Depends on experiences of the troubleshooter
 Substitution
– problem assumed to be caused by a specific part
– the solution – replace the part
– used for inexpensive items
• cables, NICs, etc
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9.1.3 Approaches to Troubleshooting
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9.2.1 Utilities Used to Detect Physical Problems
 Use your senses
 Sight—cables not
connected or in the
wrong order
 Smell—overheating
 Touch—overheating
 Hearing—sounds of
fans running too
much, or grinding of
the hard drive
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9.2.2Utilities Used to Verify TCP/IP Connectivity
 IP Config
– checks to make sure correct IP and subnet mask
 Ping
– verifies connectivity to other hosts
 Tracert
– traces the route of the packet
–Determines the location of delay for a
packet traversing the internet
 Netstat
– show what networks are active
 Nslookup
– asks the name server for information to determine if a DNS
server is providing name resolution
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9.2.3 IP CONFIG commands
 Ipconfig - displays current IP configuration
– IP address
– Subnet Mask
– Default Gateway
 Ipconfig /all – displays additional information
–MAC Address
–DHCP server and lease info (if enabled)
– DNS information
 Ipconfig /release – used with DHCP
– release IP address
 Ipconfig /renew – used with DHCP
– refreshes IP (requests IP configuration from a DHCP Server
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PACKET TRACER ACTIVITY
ACTIVITY 9.2.3
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9.2.4 The Ping Command
 Used to determine whether or not the host is reachable
 Can be used with either an IP address of name of
destination
 Echo request – ping sent
 Echo reply – destination host responds
 Ping issues
– able to ping both IP and name, but unable to access application
• problem likely at destination host
–Unable to ping both IP and name
• network connectivity problem
• if able to ping default gateway, problem not at local level
–Ping to IP works, but name doesn’t
•Problem is with DNS
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PACKET TRACER ACTIVITY
ACTIVITY 9.2.4
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9.2.5 The Tracert Command
 Shows each hop along the way
 Tells how long it takes for the packet to be sent and get a
response (round trip time)
 30 hops – network/user deemed unreachable
– default settings
– can be changed by adjusting the –h parameter
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9.2.6 The Netstat Command
 Views open (running) connections on a host
 Used when performance appears to be compromised
 Informs user about:
– protocols
– local address
– port numbers
– connection state
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9.2.7 The Nslookup Command
 Allows end user to look up information about DNS name in the
DNS server
 Used as a troubleshooting tool to see if DNS server has the
correct IP with the correct name
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9.3.1Hardware and Connection Issues in Wired &
Wireless Networks
 Use divide-and-conquer technique
 To determine where the problem exists:
– ping from wireless client to default gateway to verify wireless is
working properly
– ping from wired client to default gateway to verify that wired is working
properly
– ping wireless client to wired client
to verify that the integrated router
is functioning properly
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9.2.3 LED Indicators
 Used to show activity or to convey information
 Security LED
– solid green = security enabled
 Link Lights
– solid green = plugged in with no traffic
– flashing green = plugged in with traffic
– amber = making adjustments
 Power LED
– solid green = operational
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9.3.3 Cable Issues
 One of the most common problems
 Check for:
– correct cable type KNOW WHEN TO USE EACH KIND OF CABLE
–Straight through—devices that aren’t the same (EX: computer to switch)
–Cross over—devices that are the same (EX: computer to computer)
–Rollover—used to configure a router through the console port
– improper cable termination
–Too much untwisting
– too long of cable runs
– verify correct ports
– protect cables from damage
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9.3.3 Cable Issues
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Rollover
cables use
this kind of
plug to plug
into the
comport of
the
computer
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9.3.4 Radio Problems with a Wireless Network
 What if . . .
– the wireless client is unable to connect to the access point but
wired can
 Possible fixes:
– check wireless standards being used
– check channels
– check signal strength
• may be too far away from AP
– check for outside interference
–Check WEP key is correct
– check available bandwidth
• too many clients on one channel
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Association and Authentication Issues
 The following three settings must match on the
client and access point for a wireless connection to
occur
• SSID
–make sure client is configured with the correct SSID
• Check Authentication
– open (by default)
– might have be changed
– check to make sure the correct key is being used
• Encryption
– key needed by the client
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DHCP Problems
 Make sure the IP address of the client is on the same
network as the ISR
 If both client and access point are not on the same
network, use release and renew
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9.3.6 ISR Router to the ISP Problems
 Wired and Wireless devices can
connect to each other, but not
the Internet . . . Why??
 May be a connection between
the access point and the ISP
– check out the router status page
– check physical connections
(including indicator lights)
– verify passwords
– may be that the Internet site is just
down
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Documentation
 Set a performance baseline
– do this just after the network is installed and running efficiently
 When documenting a problem, include the
following
– initial problem
– steps taken
– result of the steps
– determined cause of problem
– how the problem was resolved
– preventive measures taken
–Keep a record of system upgrades
and software versions
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Using the Helpdesk
 Provides assistance for the end user to help fix a problem
– via email
– via live chat
– via phone
 Use of remote access
– help desk takes control of your machine
 Inform the help desk of the following:
– symptoms
– who had the problem
– when it happened
– steps taken
– results of steps taken
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Summary
 Effective troubleshooting combines instinct, experience, and
structured techniques to identify, locate, and correct network or
computer problems.
 Documentation is essential in effective troubleshooting, and should
contain baseline information about the network.
 A large proportion of networking problems relate to physical
components.
 Many networking problems can be identified with software utilities
such as ping, tracert, and netstat.
 In a network containing both wired and wireless connections, it is
important to isolate the problem to either the wired or wireless
network.
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ITE PC v4.0
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