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