Solutions Through IT

March 22, 2011

Why does it take so long to make changes to websites or emails (DNS Changes)

Filed under: Cloud, DNS, Hosting — solutionsthroughit @ 09:43

This is a very quick introduction to DNS and how it functions.  This article is written at a high level (not overly technical) to help explain why this process can take up to three days to finalise changes.

When you type a website address or email address into your computer, and send the webpage request or email on it’s way to the internet, a few things happen in the background.  Your computer will talk to a DNS server, either your ISP’s or offices, and ask it for the IP address for the domain that you are trying to contact.  If your DNS server has previously requested this, it will return it to you, or will go out and find it.  The DNS record (or IP address) also has other information associated with it, including an expiry date – effectively a “do not use this IP address from cache after this time”.

Some ISP’s (Telstra and Optus are/were know to do this) ignore the expiry date for the record, and continue to cache the IP address for up to 72 hours.  This means that even if you expire your IP address record after 15 minutes, they will hold the address well after it has expires.

Scenario: A customer using Telstra visits your website.  You change the website address, knowing that compliant DNS servers will show the website correctly after 15 minutes (expiry time for your DNS).  Any other customer using Telstra will not be able to “see” the new website until 72 hours from the first customer had visited your website.  If we are talking about email instead of websites, this will mean that emails can BOUNCE back at the sender who is trying to send you emails!


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