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 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..
Manich Enterprise gives you complete control over
the following Resource Records by using our Managed DNS Service:
I. 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.
II. Mail Exchanger
[MX] Record
A 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.
A 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.
III. Canonical 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 companies register their multiple
domain names for their brand-names but still wish to maintain a single website.
In such cases, a CNAME Record maybe used to forward traffic to their
actual website. For example, www.abc.in could be CNAMEd to www.abc.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 adding a CNAME-record for the www name
pointing to the short name [while creating an A Record for the short name
(without www)].
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.
IV. 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 a 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.
V. Text [TXT] RecordA Text Record provides the ability to associate some text with a domain or
a subdomain. This text is meant to strictly provide information and has no
functionality as such. A TXT Record can store upto 255 characters of free form
text. This record is generally used to convey information about the zone.
Multiple TXT records are permitted but their order is not necessarily retained.
For example, you may add a TXT Record for
yourname.com with the value as "This is my mail server". Here if
anybody was checking ALL or TXT records of yourname.com, they would notice
the above text appearing in the TXT record.
TXT Record is also used to implement the Sender
Policy Framework (SPF) and DomainKeys specifications.
Sender Policy Framework (SPF)
Sender Policy Framework is an extension to the
Simple Mail Transfer Protocol (SMTP). SPF allows software to identify and reject
forged addresses in the SMTP MAIL FROM (Return-Path), a typical nuisance in
e-mail spam.
SPF allows the owner of a domain to specify
their mail sending policy, e.g. which mail servers they use to send mail from
their domain. The technology requires two sides to work in tandem -
i. the domain owner publishes this information
in an TXT Record in the domain's DNS zone, and when someone else's mail server
receives a message claiming to come from that domain, then
ii. the receiving server can check whether the
message complies with the domain's stated policy. If, for example, the message
comes from an unknown server, it can be considered a fake.
Click here to find more
information on SPF and how you may use it to authenticate mails being sent from
your domain name >>
DomainKeys
DomainKeys is an e-mail authentication system
(developed at Yahoo!) designed to verify the authenticity of the E-mail sender
and the message integrity (i.e,. the message was not altered during transit).
The DomainKeys specification has adopted aspects of Identified Internet Mail to
create an enhanced protocol called DomainKeys Identified Mail (DKIM).
Click here to
find more information about DomainKeys and how you can prove and protect an
Email Sender's identity >>
VI. Start of Authority [SOA] Parameters
Each Zone contains
one SOA Record, which holds the following parameters 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.).