Transcript 110.03 Presentation File

Resolve common problems with
wired and wireless networks.
Objective 110.03 – 2%
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Network Troubleshooting
In any network there are likely to be failures over
time.
The larger, more complex the network the more
likely there are to be problems.
To effectively solve problems a consistent approach
should be taken.
 Simplify as much as possible.
 Use the OSI model as a checklist.
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Network Troubleshooting
If there are multiple devices exemplifying a problem
try to isolate the devices first to simplify the
situation.
Once the situation can no longer be simplified begin
searching for the source of the problem.
Start at the lowest layer and work up the OSI model.
For example:


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Start by checking wires and connections (Layer 1:
Physical).
Next proceed to checking the NIC (Layer 2: Data Link).
Then check IP settings (Layer 3: Network).
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Software and Hardware Tools
To locate the source of the problem there are many
tools that can be of assistance.
There are also tools that are more applicable to use
once the source of the problem has been located.
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Hardware Tools
Cable Tester
 Used to check network
cables for continuity.
 Checks each individual wire
in a twisted pair cable.
Loopback Plug
 Used to check a network
interface.
 Sends data directly back to
the interface from which it
comes.
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Hardware Tools
 Toner Probes
 Used to locate the end of a wire
within a bundle of other wires.
 Attach sender to known
location.
 Use receiver to locate other
end.
 Wireless Locator
 Used to analyze the surrounding
networks.
 Good for determining signal
strength.
 Good for troubleshooting
interference.
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Hardware Tools
Punch Down Tools
 Useful if wire has come
loose from a patch panel.
Cable Strippers
 Removes the sheath of a
wire so that the wire can
be repaired.
Crimper
 Allows for the attachment
of an Registered Jack (RJ)
tip.
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Software Tools
Ipconfig
 Shows current IP
addresses.
 Can release and
renew IP
addresses.
Ping
 Tests connectivity
to an IP address.
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Software Tools
Tracert
 Traces the route
to an IP address.
Pathping
 Combination of
ping and
traceroute.
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Software Tools
Netstat
 Reports all
active
connections on
an interface.
Nbtstat
 Reports all hosts
that are
connected via
NetBios.
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Software Tools
Net
 Reports or assigns many network attributes
depending on the options used.
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Common Symptoms & Solutions
Now that we have a troubleshooting method and a
few tools we can take a look at some of the most
common networking problems and their likely
solutions.
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•
•
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No connectivity
Limited connectivity
Local connectivity
APIPA address
•
•
•
•
Intermittent connectivity
Slow transfer speeds
Low RF signal
IP conflict
*Note that we cannot cover all possible problems or solutions because there
are too many.
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No Connectivity
Wired
This state occurs when there is a physical media
problem or a bad network card.
Check the network cable first (layer 1) then
troubleshoot the NIC (layer 2) if the cable is verified
as working.
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No Connectivity
Wireless
This state occurs if the WNIC has not been
associated with a network.
Try to connect to a network.
If that fails check to make sure you have the proper
wireless passphrase for the SSID you are attempting
to connect to.
If there is still failure start at layer 1 and you have
made sure there is no wireless interference. Then
move to layer 2 and check the WNIC. Often
improper WNIC drivers can cause this situation.
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LAN Connection, No Internet Access
Limited Connectivity
Your PC is getting an IP address from the DHCP
server, but there is no Internet access.
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LAN Connection, No Internet Access
Local Connectivity
Automatic Private IP Addressing (APIPA)
These two are very closely related.
When only local connectivity is available, the PC is
not getting an IP address from a DHCP server even
though it is configured to do so.
To make up for the lack of IP address, and so that the
computer can communicate with other PCs on the
network, it uses the reserved APIPA addresses which
all begin with 169.254.x.x.
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LAN Connection, No Internet Access
When these previous situations occur:
Layer 1 and Layer 2 are ruled out because we have
verified connection.
The problem lies with either a gateway router (layer
3) for Limited Connectivity or a DHCP server (layer 7)
for Local Connectivity.
In either scenario, a check and reset of the device in
question will likely fix the problem.
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Intermittent Connectivity
A situation in which your network state goes from
connected to disconnect at random intervals.
This is often caused by a layer 1 problem.
A loose RJ-45 connector with a broken or damaged
retention clip can be slowly slipping out of the NIC.
A wire that has been pulled on or pressured over a
long period of time may be coming or is damaged.
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Slow Transfer Speeds
 A situation in which your file
transfers happen at speeds much
lower than your specified
bandwidth (i.e. 30 Mbps LAN
transfer with a 100 Mbps NIC).
 This is most often caused by
Intermittent Connectivity.
 If connectivity is verified as good,
then check software settings for
the NIC.
 Auto Negotiation is the
recommended setting for the
NIC .
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Low Radio Frequency (RF) Signal
 A situation in which the wireless connection exhibits either or
both of the previous two behaviors because of a weak
connection to the access point (AP)/router.
 Solutions here center around layer 1, the physical connection.
 Check to make sure that the AP/router was not moved.
 The fewer walls between the PC and the AP/router the better
the signal will be, if possible relocate the PC.
 If the solution is not as obvious as above, the use of a
Wireless Locator tool is very helpful in identifying sources of
RF interference.
 Try to eliminate as much RF interference as possible.
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IP Conflict
This situation occurs when two devices on the same
network attempt to use the same IP address.
This most often occurs when a DHCP server is
attempting to lease an IP address that has already
been assigned statically by an administrator.
The solution is to change the DHCP server’s address
range (often called a “scope”) to exclude the static IP
address.
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Troubleshooting Flowcharts
Some times even following the logical
troubleshooting process does not result in a
solution.
Troubleshooting flowcharts can be very useful to
make sure you did not overlook something simple.
A great network troubleshooting flowchart is
available here:
http://www.fonerbooks.com/network.htm
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