Download Troubleshooting Networks

Troubleshooting Networks – Wired
Lesson overview.
In this lesson, we will cover:
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Common symptoms.
Troubleshooting tools.
Common symptoms.
There are number of things that can go wrong with wired networks. Many of the common
symptoms of problems that can happen within wired networks are outlined below, along with the
most likely causes that are indicated by those symptoms.
No connectivity.
When you have no connectivity, the most probable cause is with the network interface card
(NIC). You should check your link lights, cables, and connections to help determine what
caused the no connectivity symptom.
Highlights:
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The most likely cause for no connectivity in a wired network is the NIC.
Check link lights, cables, and connections to determine the cause.
APIPA address.
If you have connectivity but you only have an APIPA address, the most likely cause is with your
DHCP server. APIPA addresses only come into play when the device is set to receive its IP
information from a DHCP server and it doesn't receive it. In short, if your IP address begins with
169.254, you should check to ensure that your DHCP server is functioning properly.
Highlights:
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The most likely cause of an APIPA address is incorrect DHCP settings.
If the address begins with 169.254.XXX.XXX, check the DHCP server.
Limited connectivity.
If you have limited connectivity, the most likely cause will depend on the connection issue—
what it is that you can’t connect to. If you can't connect to a local device, you will need to check
the device. If you can't connect to other networks, you will need to check the router.
Highlights:
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The likely cause for limited connectivity in a wired network is either the device or the
router.
If you can’t connect to a local device, check the device.
If you can’t connect to other networks, check the router.
Local connectivity only.
A default gateway is required to reach other networks. If you only have local connectivity (i.e.,
you can't connect outside of your network), the settings for the default gateway could be wrong
on either the router or on your PC. To resolve this issue, verify the default gateway configuration
on the device and the router. Additionally, the router could be offline. If this is the case, reboot
the router.
Highlights:
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A default gateway is required to reach other networks.
The settings for the default gateway could be wrong on the router or PC.
Check the default gateway configuration on the device and the router
The router could be offline and may need a reboot.
Intermittent connectivity.
If you're experiencing intermittent connectivity, there are a number of likely causes. It could be a
bad cable—one that has a short in it. It could also be caused by a NIC that is about to go down
or fail. Alternatively, it could be a bad port on the switch or router. You will need to do some
further testing to determine the most likely probable cause.
Highlights:
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The cause is more than likely one of three things: a bad cable, a NIC that’s about to go
down, or a bad port on the switch or router.
Some testing is necessary to determine the most likely probable cause.
IP conflict.
If you have an IP conflict, the most likely probable cause is a misconfigured address. This
doesn't happen very often when you're using DHCP; however, it can easily happen with static IP
addressing. If there are duplicate addresses configured, the first device on the network wins the
conflict. When the next device with the same address attempts to get on the network, it will not
be allowed to connect.
Highlights:
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The most likely cause is a duplicate address with static IP addressing.
The first device on the network wins the conflict.
Check the IP addressing scheme and IP configurations on the devices.
Troubleshooting tools.
There are both some hardware and software utility tools that will be useful in solving many
problems with a wired network. A list of them and their functionality is provided below.
Hardware tools.
Loopback plugs.
A loopback plug is used to check the functionality of your network interface card (NIC). It's a
great tool to use when you need to troubleshoot a NIC. It plugs into the NIC and, when you use
the ping utility, the utility sends a signal out the NIC and then the loopback plug sends it right
back into the NIC to verify functionality.
Cable testers.
Cable testers are used to test the integrity of a cable. They can tell you whether or not cables
are wired correctly or if there is a short in the cable.
Toner probes.
Toner probes can also be very useful, especially when you have a cable that has a short. With a
toner probe, you can trace the cable. It injects a signal into the cable and then listens for that
signal.
Punchdown tools.
Punchdown tools are helpful when you need to replace a wire into a punchdown block. These
actually place the wires into the block and trim them neatly.
Wire strippers.
Wire strippers can be used to strip the jackets off of cables. This tool will come in very handy
when replacing or repairing a cable.
Crimpers.
Crimpers are another useful tool to have when troubleshooting networks. They can be used to
secure a cable into the proper termination ends.
Highlights:
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Loopback plugs are used to check the functionality of a NIC.
Cable testers can be used to test the integrity of the cable.
Toner probes are used to trace the path of the cable.
Punchdown tools can be used to place wires in a punch down block.
Wire strippers are used to remove insulated jacket from cables.
Crimpers can be used to secure cables into the proper termination ends.
Software network utilities.
There are also a number of software network utility tools that can be helpful in troubleshooting a
wired network. They are outlined below, along with the command that is used at the C prompt.
ipconfig (Internet protocol configuration).
The ipconfig utility is used to review the IP configuration on a given node. It will give you all the
information, depending upon which switch you use in the command, about the network
configuration for that node.
Command: C:\ipconfig /all
ping.
The ping utility uses ICMP echo requests to test for basic connectivity between two nodes. It's a
great way to tell if you can get from one location to another in a quick manner.
Command: C:\ping 192.168.0.1
tracert.
The tracert utility also uses ICMP echo requests to map the path between two nodes that are on
separate networks. This utility asks for and receives a response from routers and tells you which
routers your packet is going through.
Command: C:\tracert www.google.com
netstat (network statistics).
The netstat utility is used to identify which applications or network connections are consuming
network resources. This utility allows you to see if anything is overly consuming network
resources and, thereby, causing congestion on your network.
Command: C:\netstat -a
nbtstat.
The nbtstat utility is used to troubleshoot NetBIOS name resolution issues.
Command: C:\nbtstat -A
net.
The net utility can be used to establish a path to a network share or to recover a password on a
PC. If you cannot connect to a network share, the cause may be a connectivity issue.
Command: C:\net use
What was covered.
Common symptoms.
Network troubleshooting can be tricky; many of the symptoms that are manifested can be
difficult for the end user to nail down for you. Using a solid methodology will ease the process.
Problems with NICs, cables, and settings can all interrupt the user’s ability to access the
network.
Troubleshooting tools.
Network tools can be broken out into two categories—software utilities and hardware tools.
Hardware tools include loopback plugs, cable testers, punchdown tools, toner probes, wire
strippers, and crimpers. Software utilities include: ipconfig, ping, tracert, netstat, nbtstat, and
net.