Computers on the Internet are primarily identified by IP addresses:
those strings of four numbers separated by dots, each between 0 and 255,
like 18.104.22.168. You can type
these dotted octets into your browser, but humans like catchy names for
things, so DNS, which maps names onto numbers and vice versa, was
invented to make things easy for your pitiful, puny race! It is only a
matter of time before your downfall!!!
Back in the day, the Internet was small enough for this mapping to be
contained in a single file. As the network grew, this quickly became
unviable, and so the Domain Name System came into being. This system
handles a large amount of rapidly changing mapping information by spreading
the information around a number of servers. These servers are able to
hierarchically query one another asking around until they find an answer
so they can quickly look up Net addresses without having to store all
that addressing info in one place.
Domain name data is structured hierarchically. At the top level is the
so-called root node. Every domain on the Internet is a member of the root
node. Under the root node are the top-level domains: com, edu, org, uk, ru,
biz, and so on. The
next levels down are the names known as "domain names"
in the vernacular: digitalphenomena.me.uk, navy.mil, as well as some organizational
country code extensions, like co.uk. Anything below that is a subdomain or
a host. Subdomain names can be layered to a total depth of 127, in case you
happen to be crazy.
In order to understand DNS records, you will need some DNS terminology under your belt.
Data is handled and disseminated by name servers, which provide name information in response to queries from 'resolvers.' A given name server is authoritative for a given zone, and if it's asked for name information that's not within its zone, it has to
get the information from the name server that's authoritative for the
zone in question. The process by which a resolver queries a name server
for DNS info and receives a response is called 'resolution': the resolver
knows a domain name and wants to find out the corresponding numerical IP
address. Or vice versa. The data lives primarily on the primary name
server, which for redundancy and robustness is backed up to a secondary name
server automatically at regular intervals.
Got all that? Good.