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Course Introduction

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DNS Basics

• 1hr 16min

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DNS Resource Records

• 46min

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DNS Zones

• 3hr 41min

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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

• 54min

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PowerShell for DNS

• 1hr 27min

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Troubleshooting DNS Issues - Troubleshooting Tools

• 1hr 39min

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Domain Name System and DNS Delegation


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In this video, we will demonstrate the DNS Structure. How the Domain Name System works, and present an example of DNS Delegation. Ok if you are ready let’s get started.

The DNS tree structure looks like an upside down tree with the root at the top.  

This is an illustration of the DNS tree structure. Here we have the Root Domain represented by a dot, the Top-Level Domain, the Second- Level Domain and the Sub-Domain. In this picture,

the root is at the top; it is represented by a period at the end of a name, such as training.itflee.com(.) The dot is not generally used, but it designates that the name is located at the root or highest level of the domain hierarchy.   

Here is another illustration of part of the DNS tree that further clarifies this concept. Again, the root at the top. The top-level domains are the .com’s , .gov, .edu, .net.

“.com” indicates a name registered to a business for commercial use on the internet. The second level domains are google.com, Microsoft.com, ssa, psu, cog. These names are registered by the DNS domain name registrar. Then the www are below the second level.

The important point to remember is that even though there will be domains that have names like www or mail, each name represents a unique location within the tree. For demonstration purposes both Google and PSU have mail, but www.mail.psu.edu is certainly unique from www.mail.google.com.  

So where are the domains located?  In our example, you have the Google domain, the Microsoft domain, then .SSA, PSU, COG. Then you have all the millions, or billions of .com’s .gov's, .edu’s and .net. Then you have one huge domain that encompasses all of the internet.

The Domain Name System 

The Domain Name System works by converting names to IP addresses. For example, let’s say you type google.com into your web browser. Technically, you could have typed the IP address of google.com which is but considering we normally don’t like to remember numbers we will just type in the name google.com. We will let our DNS server resolve the name to IP address for us. Once this has been completed, you will be able to perform your searches using google.com.  

DNS works like a phone list; you don’t look up the number first, you look up the name first. 

Here is another example of how the Domain Name System works and an example of DNS delegation.

We have an international sales company called Global Marketing. GM has offices in the US, UK, JP (Japan), CA(Canada) and soon will be opening offices in DE (Germany)  

The CEO’s name is Steve. Steve has just hired five new managers to manage each of the five locations.

Jim will be managing the (UK) portion; Mark is in charge of (JP), Bill is in charge of the US operation, Carol is in charge of the Canadian location. Fred is in charge of the DE operation.  

Steve is the CEO of the company, but he has just delegated control of portions of the company or (pieces of the pie) or in DNS lingo, portions of the DNS namespace.  

Phone calls that come into the headquarters will be routed to the following extensions:

Steve (HQ) – 23

Jim(UK) – 33

Mark (JP) – 43

Bill (US) – 53 Carol (CA) - 63 Fred (DE) – 73.  

Fred, the manager of DE, has decided to split up Germany into two cities. He has Joe in Berlin at ext. 83 and Phil in Munich at Ext. 93  

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