Download Ethernet Basics and Network Troubleshooting

IB 300: Advanced Computer
Sciences.
Professor: Nabil Elmjati
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What does “network does not work” mean?
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Internet down
Server down
One computer, or group of computers can’t access
network
Wing of building down
Whole building down
Understand the “path” data takes through the
network
What does work, and specifically, what does
not
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Four common network problem categories:
1.
2.
3.
4.
Everything is slow/not working
Internet is slow, server access is normal
Server access is slow/not working, Internet access
seems normal
Single computer, room of computers, area of
building is slow/not working
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Wiring/Network problems
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Ethernet loops
 Two wires to wall? (use ONE red cable)
 Use colored cables if possible.
 Count cables/computers
 Remove extra cables
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Wiring/Network problems (cont.)
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Cable too long (more than 97m)
Cable not well pressed, causing timeouts?
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Network is very busy, so it’s slow (solid
activity lights on switches)
Look at lights on switches, unplug-replug one
at a time to see if traffic returns to normal - note
the port and track it down
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Causes:
 Worm viruses/spyware
 Loop
 “Chattery Network Card” (bad drivers or bad card)
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Keep OS updates and anti-Virus software up to
date
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Can be a Router
Problem
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Turn router off and
back on
Can be a
“Upstream”
problem
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Ping around
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Ping is a computer network administration utility
used to test the reach ability of a host on an Internet
Protocol (IP) network and to measure the round-trip
time for messages sent from the originating host to a
network card on a destination computer.
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The name comes from active sonar terminology
which sends a pulse of sound and listens for the echo
to detect objects underwater. With computer
operating systems Ping or PING stands for Packet
INternet Groper but is ordinarily written as "ping"
instead of the proper acronym for which it stands.
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Get to a command prompt
XP/Win2k/Vista
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Run “ipconfig”
 Note your default gateway
 Run “Ping <default gateway>”
 No response, your router may not be working
 Run “Ping <known district server/router>
 No response, your connection to the outside world
(Geomax/T1 etc) is down
 Run “ping www.google.com”
 No response - your district’s connection to the outside world
is down
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Overloaded Wan line(s)
Can be worm/e-mail viruses eating up bandwidth
 Can be peer-to-peer file sharing program on a
computer in your school
 Streaming video/audio congesting the network?
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What you *CAN* do
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Step 1
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Un-plug/re-plug the server’s
network cables
 First Contact helpdesk/your NA.
 Don’t move them, plug them back in
the same place
 Only do one end of one cable at a
time
 The server will be “down” while they
are un-plugged
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Step 2 (still not working)
Check it out, or have the network
guy check it out
 Contact helpdesk/your NE, get
server restarted
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What do they have in common?
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All connected to same switch?
 Power-cycle switch
 Check for loops
 Change port
 Replace switch
 What do they have in common? (cont.)
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All same model/from same image?
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Virus/Spyware in image?
Client software installed/configured wrong?
OS not patched?
Bad NIC driver?
Same “wing” or area
 Power cycle switches
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Restart the computer
Un-plug/re-plug/replace
cables
Check it’s connection at
Switch or hub
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Change it’s port
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Don’t move other wires
Don’t “clean up” wiring!!!
If it doesn't fix it, change it
back
Patches/ AntiVirus /
Spyware
Upgrade/Re-install NIC
driver
Replace NIC
Force speed/duplex (gig
switch, Cat5 wiring?)
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Before trying to fix any issue regarding you
home network or internet you will need to
understand how the network is set up in your
house.
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Internet not Working!
First: Check if your computer has an IP address
If you don’t have an ip, check if your NIC is
properly working.
Second: Ping your router.
If there is no response power cycle your router
Third: Plug-in directly to your router (turn off
Wifi) or check another computer on your
network, to see if you are the only one affected.
Fourth: Log in to your router to see if you are
connected to your ISP. If not check your setting
or call your ISP
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Internet is slow!
Important: Always ask yourself before starting
your troubleshooting: is your network secure?
First: Reboot your Router. See if that fixes it.
Second: Check if someone on your network is
using filesharing softwares or video streaming.
Third: Ping your router to check the latency as well
as an IP address and hostname for a known site
like google.
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If latency is smaller when you ping the ip address of a
host, then your ISP has a DNS issue.
Fourth: Log in to your router to see if your line has
the ordered Speed from your ISP