Domain Name System (DNS)
The Domain Name System [DNS] is a distributed database, arranged
hierarchically, containing records for domain names. The DNS system's
main aim is to match a domain name to an IP Address. In order to
fulfill this role, the DNS Server contains Records [called as Resource
Records] in a Zone File, which contains the domain name and IP address
mappings for computers contained within that Zone. All Resource
Records have a TTL [Time To Live], specifying the number of seconds
other DNS servers and applications are allowed to cache the record.
Most Web Hosting companies, do not provide you with an interface
to manage your own DNS Records and/or the ability to select multiple
providers for various Services like Web Hosting, Mail Hosting, etc.
FirstWebFoundation
gives you complete control over the following Resource Records by
using our Managed DNS Service:
Address Record [A Record] - The A Record
is the most basic and the most important DNS record type. They are
used to translate human friendly domain names such as "www.domain.com"
into IP-addresses such as 1.2.3.4 (machine friendly numbers).
When you wish to host your domain name, you will be provided with
an IP address that needs to be set as an A Record for that particular
domain name.
Mail Exchanger [MX] Record - An MX Record
identifies the mail server(s) responsible for a domain name. When
sending an e-mail to user@xyz.com, your mail server must first look
up the MX Record for xyz.com to see which mail server actually handles
mail for xyz.com (this could be mail.xyz.com - or someone else's
mail server like mail.isp.com). Then it looks up the A Record for
the mail server to connect to its IP-address.
An MX Record has a Preference number indicating the order in which
the mail server should be used (only relevant when multiple MX Records
are defined for the same domain name). Mail servers will attempt
to deliver mail to the server with the lowest preference number
first, and if unsuccessful continue with the next lowest and so
on.
Canonimical Name [Alias / CNAME] Record
- CNAME Records are domain name aliases. Often computers on the
Internet have multiple functions such as Web Server, FTP Server,
Chat Server, etc. To mask this, CNAME Records can be used, to give
a single computer multiple names (aliases).
Sometimes a single server computer hosts many different domain
names (take ISPs), and so CNAME Records may be defined such as www.abc.com
= www.xyz.com.
The most popular use of the CNAME Record type, is to provide access
to a Web Server using both the standard www.domain.com and domain.com
(without the www). This is usually done by creating an A Record
for the short name (without www), and a CNAME-record for the www
name pointing to the short name.
CNAME Records can also be used when a computer or service needs
to be renamed, to temporarily allow access through both the old
and new name.
Authoritative Name Server [NS] Record -
NS Records identify DNS servers responsible (authoritative) for
a Zone. A Zone should contain one NS Record for each of its own
DNS servers (primary and secondaries). This mostly is used for Zone
Transfer purposes (notify). These NS Records have the same name
as the Zone in which they are located.
But the most important function of the NS Record is Delegation.
Delegation means that part of a domain is delegated to other DNS
servers.
You can also delegate sub-domains of your own domain name (such
as subdomain.yourname.com) to other DNS servers. An NS Record identifies
the name of a DNS server, not the IP Address. Because of this, it
is important that an A Record for the referenced DNS server exists,
otherwise there may not be any way to find that DNS server and communicate
with it.
If an NS Record delegates a sub-domain (subdomain.yourname.com)
to a DNS Server with a name in that sub-domain (ns1.subdomain.yourname.com),
an A Record for that server (ns1.subdomain.yourname.com) must exist
in the Parent Zone (yourname.com). This A Record is referred to
as a Glue Record, because it doesn't really belong in the Parent
Zone, but is necessary to locate the DNS Server for the delegated
sub-domain.
Start of Authority [SOA] Record - Each
Zone contains one SOA Record, which holds the following properties
for the Zone
Name of Primary DNS Server
The domain name of the Primary DNS Server for the Zone. The Zone
should contain a matching NS Record.
Mailbox of the Responsible Person
The email address of the person responsible for maintenance of the
Zone.
Serial Number
Used by Secondary DNS Servers to check if the Zone has changed.
If the Serial Number is higher than what the Secondary Server has,
a Zone Transfer will be initiated. This number is automatically
increased by our Servers when changes to the Zone or its Records
are made.
Refresh Interval
How often Secondary DNS Servers should check if changes are made
to the zone.
Retry Interval
How often Secondary DNS Server should retry checking, if changes
are made - if the first refresh fails.
Expire Interval
How long the Zone will be valid after a refresh. Secondary Servers
will discard the Zone if no refresh could be made within this interval.
Minimum (default) TTL
Used as the default TTL for new records created within the zone.
Also used by other DNS Server to cache negative responses (such
as record does not exist, etc.).
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