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Sun Aug 17, 2014, 06:55 PM

Computer Network Diagnostic Basics for Everyone

Last edited Mon Aug 18, 2014, 07:46 PM - Edit history (7)

The number one most requested help problem that technical support receives are problems with Network Connectivity...

They always end up having you do basic network diagnostics first.
Reboot modem
Reboot computer
Re-seat your cables…
Check for INTERNET lights on modem…

But after that…well its gets a little more technical but let’s try to break it down for everybody…

This document is to assist inexperience, NON-Technical computer users in understanding and being able to diagnose the basics of network connectivity for themselves...

This in-turn will give you confidence and a greater understanding of exactly how your computer works on the INTERNET...

Please note: This is NOT a complete diagnostic HOW TO, there needs to be a known issue before you can write a flow chart of diagnostics…

This document instead will explain in laymans terms how your computer talks to the INTERNET and what you can do yourself to understand how your connection works and where it is possibly failing.

Overview: How does my computer talk to the INTERNET anyway?

Your computer hardware(motherboard) talks (LAYERS 1+2 physical layer Transport Layer) to a modem or an Ethernet card which in turn talks to a network connection via an Ethernet cable or wireless connection…this “connection” can be a cable modem, DSL modem, Ethernet wall jack ect…what is important to know is that what we are talking about is the “Physical layer” the hardware equipment involved in connecting…computer motherboard, Ethernet card, Ethernet cables, cable modem or DSL modem…
Think of it as a line of electricity…there must be a GOOD physical and electrical link, between each piece for reliable connectivity to occur…

On top or part of this “Physical layer” are what are called the “Virtual Layers” or better known as “Layer 3 Protocol Operations”. (For more detailed info look up the 7 Layers of the OSI Model.)

Layer 3 Protocol Operations are the brains of the connection and are based on, Software on top of the Hardware…Software includes the Operating System, the TCP/IP stack, DNS service, various installed applications such as a web browser or say an online game…are considered higher levels in the OSI model but this for understanding this basic instructions lets call them layer 3+.

“Layer 3 members”

TCP/IP stack: (transmission Control Protocol/INTERNET Protocol) is the computer software that communicates with your Ethernet card and your connections…DSL or Cable modem…

This TCP/IP stack manages the Routing Protocol either Static routes or DHCP via the Ethernet card and negotiates with your cable or DSL Modem to access the INTERNET.

DNS Services: (domain Name Service) DNS is the protocol that does an INTERNET lookup that translates a domain name www.youtube.com into an IP address or IP address’s and that your Ethernet card can recognize and route to your other applications such as your web browser.

Web browser: Your web browser is a Layer 3+ software application that calls to your Ethernet card to create a communication connection to an INTERNET web site. This is done through the TCP/IP stack and the DNS service.

Ok now that we have an ideal how your computer connects to the INTERNET let’s look at the basic diagnostic tools available free in your windows operating system.

THE DOS WINDOW… also know as Command window or Command line.

This is the executable window you can use to execute basic diagnostics and can be accessed from your start menu and run command…start, run, command.exe or cmd.exe depending on windows version… you should get a black window with a prompt with your hardrive path and username something that looks like this…


Typing "help" or "?" at the command prompt will generate a list of available commands for your version of windows/DOS.

When executing commands…if you have it running and need to get back to the Prompt press CTRL+C To exit interactive mode and return to the command prompt.
Type exit at the command prompt to close the window.

Basic Windows/DOS Tools:
Traceroute (tracert)

Note: each of the executions are first by ip…this bypasses DNS Lookups…very helpful.
The next one uses a DNS lookup to complete execution and if DNS fails the execution will fail.

C:\Users\Drew>ping google2.netgear.com
C:\Users\Drew>tracert google2.netgear.com
C:\Users\Drew>nslookup google2.netgear.com

Ping: How to use ping:

Ping is useful for determining where in the network path that your connection is failing…

If you are having connectivity problems, you can use the ping command to check the destination IP address you want to reach and record the results. The ping command displays whether the destination responded and how long it took to receive a reply. If there is an error in the delivery to the destination, the ping command displays a message… if successful,

Ping reply from bytes=32 time 20ms TTL=44

If it fails the error message returned is:

"Request timed out "

You can use the ping command to:

1. Ping your computer (by address, not host name) to determine that TCP/IP is functioning. (Pinging your computer does not verify that your network adapter is functioning out to the INTERNET only internally that it is responding from the Ethernet Card.)
2. Ping the local router IP address to determine whether the router is running.
3. Ping the Routers Gateway address to see if it is responding
4. Ping beyond your local router out to the INTERNET.

Your ips for example might be:
Your computer ip address:
Your DSL modem gateway:
Your INTERNET gateway:
Ping the INTERNET:

ping to ethernet ip good ethernet card is working
ping to modem gateway good...gateway is working
ping to internet gateway address INTERNET connection to service provider is UP.
ping to good INTERNET is working through your service provider.

Ping alone doesn't mean you can surf...just that you have network connectivity...
Remeber if you attempt a ping using an IP address and it works but when you use a domain name and it fails then you have failed a DNS lookup.

If DNS lookups are failing then web pages will not load or you will be redirected to a service provider redirect page...Please see NSLOOKUP Below for Diagnosing Your DNS Problems..

Tracert: How to Use the TRACERT Utility

The TRACERT diagnostic utility determines the route to a destination by sending INTERNET Control Message Protocol (ICMP) know as echo packets to the destination and reporting back the path they took to get to the endpoint. With extended commands you can add DNS lookups along the way...

In the following example of the tracert command you will see replies from your

1. DSL LAN default gateway ip address.
-This is the ip that is the next hop from your computer
2. DSL WAN Gateway interface.
-This is the IP gateway address that your service provider assigns to your DSL router..
3. Next Hop…
-This is the IP address of the other side of the service providers gateway that will then traverse his network until it hits the INTERNET and then traverses the INTERNET until it hits

Translates to google2.netgear.com

1 DSLrouter.netgear.com
2 DSL-myINTERNETprovider.com
4. core1.myINTERNETprovider.com
5. google2.netgear.com
Trace complete.

This is a good trace and shows that it was able to get to the site...now try it with tracert google2.netgear.com and see if DNS resolves to let you do the same trace or... if it fails then DNS lookup is your likely culpret...

Tracert is useful for determining where in the network path that your connection is failing…

Through this traceroute you can see if it is internal to your network or the gateway or out on the INTERNET where the connection is failing…

Nslookup: (TESTING DNS) How to use Nslookup:

Nslookup.exe is a command-line administrative tool for testing and troubleshooting DNS servers.

This tool is installed along with the TCP/IP protocol through Control Panel.

To use Nslookup.exe, please note the following:

1. At least one DNS server must be specified in your TCP/IP stack or from your nslookup interactive command line…

2. Nslookup queries must have a trailing period so that it does not append additional domain information…example nslookup youtube.com. see the trailing period…

Nslookup.exe can be run in two modes: interactive and noninteractive.

Noninteractive mode is useful when only a single piece of data needs to be returned. The syntax for

noninteractive mode is:

nslookup -option hostname server


nslookup www.youtube.com.

This replies with the IP addresses that www.youtube.com. Responds from…

To start Nslookup.exe in interactive mode, simply type "nslookup" at the command prompt:

C:\> nslookup (enter)
Default Server: nameserver1.domain.com
-Default Server: This is your default DNS server you have set in TCP/IP or being injected via DHCP from your router or service provider…
-Address: This is the translated address for that DNS server…

Interactive mode prompt looks like this..
C:\> nslookup (enter)
Default Server: dslrouter.netgear.com

Now you can specify a DIFFERENT DNS server to test if your current DNS is the reason you are failing to get to web pages.

>server (enter)
Default server google2.netgear.com
>www.youtube.com. (enter)

name: www.youtube.com.

And...If you determine it is your Service Providers DNS that is causing you all these headaches well you can go into your TCP/IP stack and change your DNS from dynamic to Static and enter Google DNS and for secondary.

How to get to TCP/IP settings:
start button
control panel
network sharing
click on change adapter settings..
right click on ethernet or wireless adapter
go to properties
click on the words tcp/ip V4 protocol to highlight line
click on properties
change DNS from dynamic to use the following settings...
enter google DNS IP addresses

And there you go...

Hope this helps and is not too confusing…

With the use of ping, tracert and nslookup

you can determine if you are connected and/or where your connection is failing to work properly for the INTERNET and web browsing…

It has been pointed out to me that I am not strickly adhering to the 7 layer OSI Model...please understand I have tried to reduce this to the most basic knowledge so that you will have a quick understanding of basic network diagnostics...For me to detail the 7 layers would be more information than I believe most need for understanding ping, tracert and nslookup.

For more detailed analysis of how communicationw works between computers and the INTERNET I encourage the curious to look up the 7 layer OSI model that all communications actually follow.

Video Link to 7 layer OSI model training:


Links to more detailed commands for use with ping tracert and nslookup

Thanks for reading,


11 replies, 8341 views

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Arrow 11 replies Author Time Post
Reply Computer Network Diagnostic Basics for Everyone (Original post)
Drew Richards Aug 2014 OP
TygrBright Aug 2014 #1
Drew Richards Aug 2014 #2
TygrBright Aug 2014 #5
Drew Richards Aug 2014 #6
intaglio Aug 2014 #3
Drew Richards Aug 2014 #4
ProdigalJunkMail Aug 2014 #7
glenmarth Oct 2014 #8
Sunlei Dec 2014 #9
Name removed Feb 2015 #10
pscot Jul 2015 #11

Response to Drew Richards (Original post)

Sun Aug 17, 2014, 07:12 PM

1. Bookmarking. This is very useful!

Thank you so much for taking the time to put it all together and post it here.

Much appreciated.


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Response to TygrBright (Reply #1)

Sun Aug 17, 2014, 07:16 PM

2. You are welcome...the more i look at it the more i am thinking too much info?

People new to computers and internet might not want to wade through the explanation of how everything works they may just want... how can i test?

What you think?

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Response to Drew Richards (Reply #2)

Sun Aug 17, 2014, 08:19 PM

5. Given that we're here on DU, I think you have both...

...the folks who want a "what do I test and what does it mean and what do I do about" and nothing else, AND the folks who want to know why and how it works.

Me, I'm in the latter category so I am biased, but I think the way you've organized it, it is easy enough for someone who just wants to know how to ping to go there and concentrate on just that.


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Response to TygrBright (Reply #5)

Sun Aug 17, 2014, 08:23 PM

6. Thank you again for input.

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Response to Drew Richards (Original post)

Sun Aug 17, 2014, 07:30 PM

3. I could also suggest not dismounting the USB WiFi connection

when you meant to dismount the memory stick ...

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Response to intaglio (Reply #3)

Sun Aug 17, 2014, 07:34 PM

4. Lol good one! Very true.

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Response to intaglio (Reply #3)

Mon Aug 18, 2014, 05:30 PM

7. I had one of the micro-USB wireless cards in my pc that I was replacing...

when I threw out the old case... I had forgotten to remove the micro-USB... dern.


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Response to Drew Richards (Original post)

Fri Oct 10, 2014, 03:02 PM

8. autotuning script

There is a autotuning script for fixing limited connectivity issues that will automatically reset network settings. autotuning script for limited connectivity issues

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Response to glenmarth (Reply #8)

Sat Dec 27, 2014, 03:13 PM

9. Thank you for posting that link, thats a website worth saving!

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Response to Drew Richards (Original post)

Response to Drew Richards (Original post)

Fri Jul 17, 2015, 06:06 PM

11. Are there utilities that help

organize this process? Walk you through it? It gets more complex with phones and TV's getting networked.

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