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 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.
In
Short . . . . . .
Just
as there is a single root for telephone numbers
internationally, there must be a single authoritative
root for the Internet, administered in the
public interest.
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