What is universal resolvability?

Answer 1

Universal resolvability is the ability to reach any host on the internet from any other host, using its host name and the (Internet) Domain Name System (DNS). It also involves its uniqueness and the reliability of the system.

Think of the phone system... when you dial a number, it rings at a particular location because there is a central numbering plan that ensures that each telephone number is unique. The DNS works in a similar way. If telephone numbers or domain names were not globally unique, phone calls or e-mail intended for one person might go to someone else with the same number or domain name. Without uniqueness, both systems would be unpredictable and therefore unreliable.

Ensuring predictable results from any place on the Internet is called "universal resolvability." It is a critical design feature of the DNS, one that makes the Internet the helpful, global resource that it is today. Without it, the same domain name might map to different Internet locations under different circumstances, which would only cause confusion.

When you send an e-mail to your Aunt Sally, do you care who receives it? Do you care if it goes to your Uncle Juan instead? Wait a minute… do you have an Uncle Juan? Then whose Uncle Juan received it? Do you care if it reaches Aunt Sally if you send it from work but my Uncle Juan if you send it from home?

Of course you care who receives it... that's why you wrote it in the first place. Whether you're doing business or sending personal correspondence, you want to be certain that your message gets to the intended addressee.

If at any point the DNS must make a choice between two identical domain names with different IP addresses, the DNS would not function. It would not know how to resolve the domain name. When a DNS computer queries another computer and asks, "are you the intended recipient of this message?", "yes" and "no" are acceptable answers, but "maybe" is not.