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NETWORK TROUBLESHOOTING
IB 300: Advanced Computer
Sciences.
Professor: Nabil Elmjati
Ethernet Troubleshooting
What does “network does not work” mean? 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
Common problems
Four common network problem categories:
1. Everything is slow/not working2. Internet is slow, server access is normal3. Server access is slow/not working, Internet
access seems normal4. Single computer, room of computers, area of
building is slow/not working
Everything is slow/not working
Wiring/Network problems Ethernet loops
Two wires to wall? (use ONE red cable) Use colored cables if possible.
Count cables/computers Remove extra cables
Everything is slow/not working (cont.)
Wiring/Network problems (cont.) Cable too long (more than 97m) Cable not well pressed, causing timeouts?
Everything is slow/not working (cont.)
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 Causes:
Worm viruses/spyware Loop “Chattery Network Card” (bad drivers or bad card)
Keep OS updates and anti-Virus software up to date
Internet is slow/not working (cont.)
Can be a Router Problem Turn router off and
back on Can be a
“Upstream” problem Ping around
What is Ping
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.
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.
Ping around Get to a command prompt XP/Win2k/Vista
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
Internet is slow/not working
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?
Server is slow/not working What you *CAN* do
Step 1 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 Step 2 (still not working)
Check it out, or have the network guy check it out
Contact helpdesk/your NE, get server restarted
Group of computers is slow/not working
What do they have in common? All connected to same switch?
Power-cycle switch Check for loops Change port Replace switch
Group of computers is slow/not working (cont.)
What do they have in common? (cont.) All same model/from same image?
Virus/Spyware in image? Client software installed/configured wrong? OS not patched? Bad NIC driver?
Same “wing” or area Power cycle switches
Single computer is slow/not working
Restart the computer Un-plug/re-plug/replace
cables Check it’s connection at
Switch or hub
Single computer is slow/not working (cont.)
Change it’s port 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?)
Troubleshooting Internet at home
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.
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
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. 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
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