Ethernet Basics and Network Troubleshooting
Download
Report
Transcript Ethernet Basics and Network Troubleshooting
IB 300: Advanced Computer
Sciences.
Professor: Nabil Elmjati
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
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
Wiring/Network problems
Ethernet loops
Two wires to wall? (use ONE red cable)
Use colored cables if possible.
Count cables/computers
Remove extra cables
Wiring/Network problems (cont.)
Cable too long (more than 97m)
Cable not well pressed, causing timeouts?
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
Can be a Router
Problem
Turn router off and
back on
Can be a
“Upstream”
problem
Ping around
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.
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
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?
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
What do they have in common?
All connected to same switch?
Power-cycle switch
Check for loops
Change port
Replace switch
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
Restart the computer
Un-plug/re-plug/replace
cables
Check it’s connection at
Switch or hub
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?)
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