ICANN
manages the root DNS domains, under which
are the top-level domains. It also
manages:
- Organizational
domains
- Geographical
domains
- Reverse
domains
Beneath
the top-level domains are other naming
authorities such as Nominet, the UKs
naming authority.
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
complete.
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 and effectively.
A
typical query may run as follows:
Client
contacts Nameserver A looking for www.discountdomainsuk.com.
Nameserver
A checks its cache, but cant answer, so
it queries a server authoritive for the
Internet root.
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 www.discountdomainsuk.com.
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.
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