Understanding DNS Propagation

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Understanding DNS Propagation

Over the years we have had to explain how DNS (Domain Name Services) works to many people. The following analogy is a good explanation:
 

When you type a web address into your browser your computer sends a request to a DNS server out on the internet and asks what the address of the site is.
 

This is as if to send a letter via the post office all you would have to do is write a person's name on an envelope and nothing else.
 

For this to work the post office would need to have two things:

  1. Every person in the world would have to have a completely unique name.
  2. The post office would need a cross reference of unique name to that person's current street address.

 

This is exactly how DNS works. Every website name is unique. And DNS servers are like post offices where a record of what address each person resides at is kept.
 

Just like you have a unique street address that you reside at every web server has a unique address where it may be found on the internet such as: 192.168.1.1.
 

To register a new name with the post office you would simply go to your local post office and give them the new unique name and address.
 

Each individual post office would need to have a person assigned to call every other post office each day and compare their lists of people and addresses. This way every post office would have the same list.
 

However, since it would take time to compare lists some post offices might not have a person's address yet, or might have an old address until the update reaches them.
 

This is propagation. When the address a website resides at is first created or is changed it may take up to 72 hours for all the DNS servers (post offices in this analogy) to receive the new information.

Depending on which DNS server a person's computer happens to contact when a website name is typed in, they may or may not get the proper website server address until full propagation around the world is complete.

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