The Domain Name
System: A Non-Technical Explanation – Why Universal Resolvability Is Important
What is the Domain Name System?
The Domain Name System (DNS) helps users to find their way around the
Internet. Every computer on the Internet has a unique address – just like a
telephone number – which is a rather complicated string of numbers. It is
called its "IP address" (IP stands for "Internet Protocol").
But it is hard to remember everyone's IP address. The DNS makes it easier
by allowing a familiar string of letters (the "domain name") to be used
instead of the arcane IP address. So instead of typing 192.0.34.65, you can
type http://www.icann.org/. It is a
"mnemonic" device that makes addresses easier to remember.
Translating the name into the IP address is called "resolving the domain
name." The goal of the DNS is for any Internet user any place in the world to
reach a specific website IP address by entering its domain name. Domain names
are also used for reaching e-mail addresses and for other Internet
applications.
What is universal resolvability and why is it important to users?
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.
Where does ICANN come in?
This is where ICANN comes in . . . ICANN is responsible for managing and
coordinating the DNS to ensure universal resolvability.
ICANN is the global, non-profit, private-sector coordinating body acting in
the public interest. ICANN ensures that the DNS continues to function
effectively – by overseeing the distribution of unique numeric IP addresses
and domain names. Among its other responsibilities, ICANN oversees the
processes and systems that ensure that each domain name maps to the correct IP
address.
What goes on behind the scenes?
Behind the scenes, the story becomes a little more complicated.
In an Internet address – such as icann.org – the .org part is known as a
Top Level Domain, or TLD. So-called "TLD registry" organizations house online
databases that contain information about the domain names in that TLD. The
.org registry database, for example, contains the Internet whereabouts – or IP
address – of icann.org. So in trying to find the Internet address of icann.org
your computer must first find the .org registry database. How is this done?
At the heart of the DNS are 13 special computers, called root servers. They
are coordinated by ICANN and are distributed around the world. All 13 contain
the same vital information – this is to spread the workload and back each
other up.
Why are these root servers so important? The root servers contain the IP
addresses of all the TLD registries – both the global registries such as .com,
.org, etc. and the 244 country-specific registries such as .fr (France), .cn
(China), etc. This is critical information. If the information is not 100%
correct or if it is ambiguous, it might not be possible to locate a key
registry on the Internet. In DNS parlance, the information must be unique and
authentic. Let us look at how this information is used.
Scattered across the Internet are thousands of computers – called "Domain
Name Resolvers" or just plain "resolvers" - that routinely cache the
information they receive from queries to the root servers. These resolvers are
located strategically with Internet Service Providers (ISPs) or institutional
networks. They are used to respond to a user's request to resolve a domain
name – that is, to find the corresponding IP address.
So what happens to a user's request to reach our familiar friend at
icann.org? The request is forwarded to a local resolver. The resolver splits
the request into its component parts. It knows where to find the .org registry
– remember, it had copied that information from a root server beforehand – so
it forwards the request over to the .org registry to find the IP address of
icann.org. This answer is forwarded back to the user's computer. And we're
done. It's that simple! The domain name icann.org has been "resolved"!
Why do we need the resolvers? Why not use the root servers directly? After
all, they contain essentially the same information. The answer is for reasons
of performance. The root servers could not handle hundreds of billions of
requests a day! It would slow users down.
If you are still with the story, you are already wondering about more
complicated names with more parts such as www.icann.org. Well, the DNS is a
hierarchical system. First, the resolver finds the IP address for the .org
registry, queries that registry to find the IP address for icann.org, then
queries a local computer at that address to find the final IP address for
www.icann.org. Just what you would expect.
It is important to remember the central and critical role played by the
root servers that store information about the unique, authoritative root.
Confusion would result if there were two TLDs with the same name: which one
did the user intend? The beauty of the Internet architecture is that it
ensures there is a unique, authoritative root, so that there is no chance of
ambiguity.
What about "alternate roots?" How do they fit into this picture?
Anyone can create a root system similar to the unique authoritative root
managed by ICANN. Many people and entities have. Some of these are purely
private (inside a single corporation, for example) and are insulated from
having any effect on the DNS. Some, however, overlap the authoritative global
DNS root by incorporating the unique, authoritative root information, and then
adding new pseudo-TLDs that have not resulted from the consensus-driven
process by which official new TLDs are created through ICANN. The alternate
root operators persuade some users to have their resolvers "point" to their
alternate root instead of the authoritative root. Others (New.net is a recent
example) also create browser plug-ins and other software workarounds to
accomplish similar effects. The one uniform fact about all these efforts is
that these pseudo-TLDs are not included in the authoritative root managed by
ICANN and, thus, are not resolvable by the vast majority of Internet users.
Why do alternate roots create a problem?
There are many potential problems caused by these unofficial, alternate
root efforts to exploit the stability and reach of the authoritative root.
These efforts are often promoted by those unwilling to abide by the consensus
policies established by the Internet community, policies designed to ensure
the continued stability and utility of the DNS.
For example:
- First, the names of
some of these pseudo-TLDs could overlap TLD names in the authoritative root
or those that appear in other alternate roots. Our familiar friend icann.org
could appear in two different roots. Your e-mail to Aunt Sally could end up
with my Uncle Juan.
- Second, the unknowing
users might not be linked to one of these alternate roots and not be able to
reach these pseudo-TLD addresses at all. Your e-mail to Aunt Sally could end
up as a dead-letter.
- Third, those
purchasing domain names in these pseudo-TLDs may not be aware of these and
other consequences of the lack of universal resolvability. Or they may be
under the impression that they are experiencing universal resolvability when
in fact they are not. They may be very upset to learn that the names they
registered are also being used by others, or that a new TLD in the
authoritative root will not include those names.
These problems are not significant so long as these alternate roots remain
very small, that is, house few domain names with little potential for
conflict. But if they should ever attract many users, the problems would
become much more serious, and could affect the stability and reliability of
the DNS itself. Users would lose confidence in the utility of the Internet.
What is ICANN's role?
ICANN's mission is to protect and preserve the stability, integrity and
utility – on behalf of the global Internet community – of the DNS and the
authoritative root ICANN was established to manage. ICANN has no role to play
with alternate roots so long as these and other analogous efforts do not
create instabilities in the DNS or otherwise impair the stability of the
authoritative root. But ICANN does have a role to play in educating and
informing about threats to the Internet's reliability and stability.
ICANN is a consensus development body for the global Internet community,
and its focus is the development of consensus policies relating to the single
authoritative root and the DNS. These policies include those that allow the
orderly introduction of new TLDs.
There are those–including operators of commercialized alternate roots–who
pursue unilateral actions outside the ICANN consensus-development process.
Many hope to circumvent these processes by claiming to establish some prior
right to a top-level domain name. ICANN, however, recognizes no such prior
claim. ICANN will continue to reflect the public policy consensus of the
global Internet community over the private claims of the few who try to bypass
this consensus.
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