Trouble-Shooting DNS Client Issues

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Scenario: 

A User calls you on the phone and tells you that she cannot get to the internet.

As you know part of a sys. admin job is helping out your users when they can’t get to the internet. For many employees, a lot of their work is done from the internet, so chances are she needs her connection up and running as soon as possible.

The question that should come to your mind, is. Does this mean that there is a problem with our network or is this a problem with the user’s machine?

  • You go to the user’s computer, open a command prompt and try to recreate the problem by typing ping google.com. You cannot ping google.com. So, does that mean the whole internet or network is down? Or is there something wrong at the local ISP?

You ask the other users and they can all get to the internet.

So, the problem is probably not the network or the internet.

  • If you have been listening to the lectures by now you know that DNS allows you to get to a target destination by using a name. Because that is what Domain Name Service does it translates that name to an IP address.
  • So now if I type ping 8.8.8.8, which is googles public DNS server.  
  • But before I press return, let’s think about this, if I cannot ping google.com by name but I can ping google.com by IP address, what would the problem be? I think we could say that it starting to look more like a DNS name resolution issue. So, now we have effectively narrowed down our list of potential causes of this problem to a possible name resolution issue.
  • And I see that I can ping 8.8.8.8
  • So, I am failing to reach google by its name but successfully reaching google by its IP address. Again, more evidence of a name resolution issue.
  • How can we check this? From the command prompt type ipconfig /all
  • The question is what is this machine using for DNS name resolution?

We can see that the DNS server is set to loopback, which is 127.0.0.1.

This effectively means that name resolution has failed because the computer is looping back to itself, and cannot get to the proper DNS server to resolve the name google.com.

  • How can we fix this?

Right click on our network icon, click Open Network and Sharing Center, click Ethernet, click properties, then click Internet Protocol Version 4 (TCPIP/IPv4), then click properties.

Here is the problem, the loopback address is configured for our Preferred DNS server.

Click in the box and type the correct IP address of our Domain Controller/DNS server

ITFDC01, which is 192.168.0.10

  • Now let’s open a command prompt and type ping 8.8.8.8. We see that works now type google.com and we are getting name resolution. Now bring up Internet explorer and we see that is working as well.
  • Trouble shooting is a skill that you will develop with time. Always when you first start with any trouble shooting issue it may seem difficult at first to solve the problem. A good troubleshooter is someone that is skilled at   narrowing down the possibilities until you find one solution that fixes the problem.

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Installing and Configuring Domain Name System (DNS)

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0/1 Lessons

Course Introduction

• 10min

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DNS Basics

• 1hr 16min

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DNS Resource Records

• 46min

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DNS Zones

• 4hr 11min

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DNS Delegation

• 50min

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DNS Security Techniques

• 36min

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Advanced DNS Topics

• 22min

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DNS Security (DNSSEC)

• 1hr 16min

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DNS Policies

• 55min

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PowerShell for DNS

• 1hr 27min

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Troubleshooting DNS Issues - Troubleshooting Tools

• 1hr 39min

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