Understanding the Domain Name System|
by Clare Lawrence
Ever wonder why DNS systems came into
existence? Efficiency. Every computer has a distinct IP address, and
the Internet needed an elite method for obtaining these addresses and
for managing the system as a whole. Enter ICANN.
The Internet Corporation for Assigned Names
and Number manages the DNS root of the Internet domain namespace.
ICANN’s role is to manage the assignment of identifiers, ensuring
that all users have unique names.
The DNS system is run by a series of
servers called DNS servers. ICANN manages the root DNS domains, under
which are the top-level domains. It also manages:
Beneath the top-level domains are other
naming authorities such as Nominet, the UK’s naming
How does a DNS Query work?
The process occurs in two parts. Firstly, a
name query begins at a client computer and is passed to DNS client
service for resolution. When the query cannot be resolved locally, DNS
servers are queried.
For example, when a web browser calls the
fully qualified domain name www.discountdomainsuk.com, the request is
passed on to the DNS client service to resolve the name by using
locally cached information. If the query is held in the cache, then the
process is complete.
If, however, the query cannot be answered
locally, the DNS client service uses a server list (ordered in
sequence) to query external DNS servers. When a DNS server receives a
query, it first checks to see if it is authoritive for that domain
name. If it is authoritive, it resolves the name, and the process is
If the DNS server is unable to resolve the
query, it in turns queries other DNS servers, using a process known as
recursion. DNS servers make use of root hints to assist in locating DNS
servers, which are able to provide the required result. In this way,
DNS queries are minimised and the Internet is able to operate quickly
A typical query may run as follows:
Client contacts Nameserver A looking for
Nameserver A checks its cache, but
can’t answer, so it queries a server authoritive for the
The root server responds with a referral
to a server authoritive for the .com domains. NameserverA queries the
the .com server and gets referred to the server authoritive for
Nameserver A queries this server and gets
the IP address for www.discountdomainsuk.com.
Nameserver A replies to the client with
the IP address.
Queries can return answers that are
authoritive, positive, negative or referral in nature. In the event of
a negative answer, another DNS server is queried.
Clare Lawrence is CEO of
Discount Domains Ltd – A
leading UK provider of domain name registration and web hosting services.