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, Email Hosting, etc..

ABC DIGITAL WEB SOLUTIONS, LLC. gives you complete control over the following Resource Records through its DNS Service:

• IPv4 Address Record [A Record]

  The IPv4 Address Record is the most basic and the most important DNS Record type. They are used to translate human friendly domain names such as yourdomainname.com into IP-addresses such as 1.2.3.4 (machine friendly numbers).

• IPv6 Address Record [AAAA Record]

  The IPv6 Address Record is the next-generation protocol for packet-switched internetworks and the Internet. IPv4 Address Record is currently the dominant Internet Protocol version. The most important feature of IPv6 Address Record is a much larger address space than that of IPv4 Address Record. Addresses in IPv6 Address Record are 128 bits long while those in IPv4 Address Records are 32 bits long.

  Note

  When you host your domain name with a Web Hosting Service Provider, you will be provided with either an IPv4 Address or an IPv6 Address and it needs to be set as an A Record or an AAAA Record respectively, for that particular domain name.

• Mail Exchanger[MX] Record

  A MX Record identifies the email server(s) responsible for a domain name. When sending an email to user@xyz.com, your email server must first look up the MX Record for xyz.com to see which email server actually handles email for xyz.com (this could be mail.xyz.com - or someone else's email server like mail.isp.com). Then it looks up the A Record for the email server to connect to its IP-address.

  A MX Record has a Preference number indicating the order in which the email server should be used (only relevant when multiple MX Records are defined for the same domain name). Email servers will attempt to deliver email to the server with the lowest preference number first, and if unsuccessful continue with the next lowest and so on.

• 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 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.yourdomainname.com and yourdomainname.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.

• 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 secondary). 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.yourdomainname.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.yourdomainname.com)to a DNS Server with a name in that sub-domain (ns1.subdomain.yourdomainname.com), an A Record for that server (ns1.subdomain.yourdomainname.com) must exist in the Parent Zone (yourdomainname.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.

• Text [TXT] Record

  A TXT Record provides the ability to associate some text with a domain or a sub-domain. 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 yourdomainname.com with the value as "This is my email server". Here, if anybody was checking ALL or TXT Records of yourdomainname.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. 1. The technology requires two sides to work in tandem:

  • The domain owner publishes this information in an TXT Record in the domain's DNS zone, and when someone else's email server receives a message claiming to come from that domain, then

  • 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.

  DomainKeys

  DomainKeys is an email authentication system (developed at Yahoo!) designed to verify the authenticity of the email 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). 2

• Service [SRV] Record

  A SRV or Service Record is a category of data in the DNS specifying information on available services. When looking up for a service, you must first lookup the SRV Record for the service to see which server actually handles it. Then it looks up the Address Record for the server to connect to its IP Address.

  The SRV Record has a priority field similar to an MX Record's priority value. Clients always use the SRV Record with the lowest priority value first, and only fall back to other SRV Records if the connection with this Record's host fails. If a service has multiple SRV records with the same priority value, clients use the weight field to determine which host to use. The weight value is relevant only in relation to other weight values for the service, and only among SRV Records with the same priority value.

  Newer Internet Protocols such as SIP (Session Initiation Protocol) and XMPP (Extensible Messaging and Presence Protocol) often require SRV support from clients.

• 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 utomatically 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.).

1. 1. Information about SPF and how you may use it to authenticate mails being sent from your domain name
2. 2. Information about DomainKeys and how you can prove and protect an Email Sender's identity