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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. ICANNs 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:
- 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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