While working as the Webmaster for a small enterprise we had the need to change the hosting provider for our web server. The last step of this migration was to repoint the domain names from the old server to the new server. I was asked why it would take “up to 72 hours for the DNS to propagate” – that seemed like too long to this person.
I explained that our Domain Names were like names in a phone book. If you want to call someone, you have to look up their phone number in the phone book (or your smartphone’s contact list, etc.). Just like people’s phones, computers have “phone numbers”, too! And we were changing our web site’s “phone number”.
“Okay, sure, but all that takes it one phone call, and it’s updated. It should take 3 days!”
My reply: “Well, imagine that our old phone number has been associated with our company for several years. People still have phone books from years ago which they’re using to look up our number, they still have business cards and brochures with our old number, all the contracts, address books, and Rolodexes that every single one of our customers around the globe has displays our old phone number. So, in less than 72-hours, I’m going to change all of those old entries for our web server’s ‘phone number’ – how long will it take you to call all of your old contacts and have them update your phone number to a new one?”
“Uh, probably a few days…”
“Now multiply that by every employee in the company (since the company started doing business, including those who no longer work here) and make sure nobody misses anyone. 72-hours is actually REALLY impressive, all things considered. And I bet it’ll take less time than that.”