Managing DNS Resource Records

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 Resource Records (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 Time To Live TTL (TTL), specifying the number of seconds other DNS servers and applications are allowed to cache the Record.

Types of Resource Records (RRs) manageable through BlueHost China's DNS Service

  • Address (IPv4 A) Record (Anchor: defa): These are used to translate domain names into IP addresses.

  • AAAA (IPv6) Record (Anchor: defaaaa): The IPv6 Address Record is a much larger address space than that of a IPv4 Address Record. Addresses in IPv6 Address Records 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 company, you will be provided with either an IPv4 Address or an IPv6 Address. This needs to be set as an A Record or an AAAA Record respectively, for that particular domain name.

  • Mail Exchanger (MX) Record (Anchor: defmx): An 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 looks 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.

    An MX Record has a Preference number, indicating the order in which the email server should be used. 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 (CNAME) Record (Anchor: defcname): 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.

    Example:

    www.abc.in could be CNAME to www.abc.com.

    The most popular use of the CNAME Record, 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 shorter 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.

  • Name Server (NS) Record (Anchor: defns): NS Records identify the 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.

    The most important function of the NS Record is Delegation. Delegation implies 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 an 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) Records (Anchor: deftxt): TXT Records provide 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.

    Example:

    You may add a TXT Record for yourdomainname.com with the value as This is my email server. Here, if anybody was checking the TXT Records of yourdomainname.com, would notice the above text appearing in the TXT Record.

    TXT Record can be used to implement the following:

    • 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). 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 name. See details. 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). See details

  • Service (SRV) Record (Anchor: defsrv): An 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) Record (Anchor: defsoa): Each Zone contains a single SOA Record, which holds the following values 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 the 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 DNS servers when changes to the Zone or its Records are made.

    • Refresh Interval: How often the Secondary DNS servers should check if changes are made to the zone.

    • Retry Interval: How often the 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 servers to cache negative responses (such as Record does not exist, etc.).

To Manage Resource Records

  1. Login to your Control Panel, search for the domain name and proceed to the DNS Service interface. See details

  2. Click the Manage DNS link. The DNS Management Console will pop-up through which you may add any of the following Records:

    Note

    • The DNS Service gets activated, when you click the Manage DNS link for the first time.

    • For Resellers: The DNS Management Console will be displayed only if the Order belongs to a Customer immediately under you. Otherwise, the below error message with be displayed:

      Attention

      You are not allowed to perform this action.

    • To Manage A Records (Anchor: ma):

      1. Click A Records and in the next screen, click Add A Record.

      2. There you would find 3 fields:

        • Host Name: Here the domain name, for which you are adding the A Record for, would be pre-filled (e.g. yourdomainname.com). Now, if you wish to add an A Record for my.yourdomainname.com, then you would have to put in my the text box. If you wish to add A Record for just yourdomainname.com, then you can leave this box blank.

        • Destination IPv4 Address: Here you would have to enter the IPv4 IP Address of the Web Server, where you wish to host this domain name.

        • TTL: This is the Time To Live for this Record, in seconds. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

      3. Click the Add Record button to submit your Record.

      Note

      Similarly, to Modify or Delete an A Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    • To Manage AAAA Records (Anchor: maaaa):

      1. Click AAAA Records and in the next screen, click Add AAAA Record.

      2. There you would find 3 fields:

        • Host Name: Here the domain name, for which you are adding the AAAA Record for, would be pre-filled (e.g. yourdomainname.com). Now, if you wish to add an AAAA Record for my.yourdomainname.com, then you would have to put in my the text box. If you wish to add AAAA Record for just yourdomainname.com, then you can leave this box blank.

        • Destination IPv6 Address: Here you would have to enter the IPv6 IP Address of the Web Server, where you wish to host this domain name.

        • TTL: This is the Time To Live for this Record, in seconds. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

      3. Click the Add Record button to submit your Record.

      Note

      Similarly, to Modify or Delete an AAAA Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    • To Manage MX Records (Anchor: mmx):

      1. Click MX Records and in the next screen, click Add MX Record.

      2. There you would find 4 fields:

        • Zone: The domain name for which you setting an MX Record needs to be entered as the Zone. If you are configuring the email server for yourdomainname.com, such that you can receive mails@yourdomainname.com, then you need to leave this field blank.

        • Value: This is the email server domain name. If the email servers hosting your domain name are managed by you, then you may set the Value in the format: mail.yourdomainname.com.

          If you are using another Internet Service Provider's email server, then you need to enter a Fully Qualified Domain Name (FQDN) like mail.isp.com.

          Note

          A Fully Qualified Domain Name always has a "." in the end.

        • TTL: This is the Time To Live for this Record. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

        • MX Priority: An 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.

      3. Click the Add Record button to submit your Record.

      Note

      Similarly, to Modify or Delete an MX Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    • To Manage CNAME Records (Anchor: mcname):

      1. Click CNAME Records and in the next screen, click Add CNAME Record.

      2. There you would find 3 fields:

        • Host Name: If you wish to Add a CNAME Record for yourdomainname.com like manage.yourdomainname.com or www.yourdomainname.com, then enter the Host Name as manage or www in this text box.

        • Value: This is the Destination for the CNAME created. Thus, if you wish to create a CNAME Record for www.yourdomainname.com pointing to yourdomainname.com, then you would have to enter yourdomainname.com. in this text box.

        • TTL: This is the Time To Live for this Record. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

      3. Click the Add Record button to submit your Record.

      Note

      Similarly, to Modify or Delete an CNAME Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    • To Manage NS Records (Anchor: mns):

      1. Click NS Records and in the next screen, click Add NS Record.

      2. There you would find 3 fields:

        • Zone: If you wish to create a Name Server for a sub-domain like ns1.subdomain.yourdomainname.com, then enter the Zone as subdomain.yourdomainname.com in this text box.

        • Value: This is the Name of the Name Server to be created or another Fully Qualified Domain Name that you want to make responsible for this Zone. Thus, if you wish to create an NS Record for subdomain.yourdomainname.com, you may enter the value as ns1.subdomain.yourdomainname.com. Or, you may want a Name Server like ns1.subdomain.yourdomainname.com to be delegated to another Fully Qualified Domain Name like dns1.anyotherns.com.

        • TTL: This is the Time To Live for this Record. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

      3. Click the Add Record button to submit your Record.

      Note

      Similarly, to Modify or Delete an NS Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    • To Manage TXT Records (Anchor: mtxt):

      1. Click TXT Records and in the next screen, click Add TXT Record.

      2. There you would find 3 fields:

        • Host Name: If you wish to Add a TXT Record for yourdomainname.com like yourdomainname.com, then leave the Host Name text box blank.

        • Value: 255 characters of free form text can be provided in this field. This Record is generally used to convey information about the zone.

          For example, you may add a TXT Record for mail.yourdomainname.com with the value as This is my email server. Here if anybody was checking ALL or TXT Records of mail.yourdomainname.com, they would notice the above text appearing in the TXT Record.

        • TTL: This is the Time To Live for this Record. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

      3. Click the Add Record button to submit your Record.

      Note

      Similarly, to Modify or Delete an TXT Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    • To Manage SRV Records (Anchor: msrv):

      1. Click SRV Records and in the next screen, click Add SRV Record.

      2. There you would find 7 fields:

        • Service Record Name: The Service Record Name consists of the symbolic Service Name and the Protocol Name of the desired service.

          • Service Name: This is the symbolic name of the desired service. For example, chat, sip, etc.

          • Protocol Name: The protocol of the desired service, usually either TCP or UDP.

        • Priority: The priority of the target host. A lower value indicates higher priority.

        • Weight: A relative weight for Records with the same Priority.

        • Port: The TCP or UDP port on which the service is to be found.

        • Target: The canonical hostname of the machine providing the service. If the Server providing the service is managed by you, then you may set the Value in the format: service.yourdomainname.com.

          If you are using another Internet Service Provider's Server, then you need to enter a Fully Qualified Domain Name like service.isp.com.

          Note

          A Fully Qualified Domain Name always has a "." in the end.

        • TTL: This is the Time To Live for this Record, in seconds. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

      3. Click the Add Record button to submit your Record.

      Note

      Similarly, to Modify or Delete an SRV Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    • To Manage SOA Records (Anchor: msoa):

      The moment you activate the DNS Service provided by BlueHost China, a default Start Of Authority [SOA] Record is created for your domain name. To modify your SOA Record:

      1. Click SOA Parameters and in the next screen, click Modify Record.

      2. There you would find 5 editable fields:

        • Responsible Person: The email address of the person responsible for maintenance of the Zone.

        • Refresh: The Refresh Interval indicates how often Secondary Name Servers should check if changes are made to the Zone. You can decide your own value for this Interval. Value should not be less than 7200, i.e., 2 hours.

        • Retry: The Retry Interval indicates how often the Secondary Name Servers should retry checking, if changes are made - if the first refresh fails. Value should not be less than 7200, i.e., 2 hours.

        • Expire: The Retry Interval indicates 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. Value should not be less than 172800, i.e., 48 hours.

        • TTL: This is the Time To Live for this Record. Any Server which once queries this Record will query it again after this time interval. The ideal TTL is 86400, which is 1 day. It can not be set to less than 14400, i.e., 4 hours.

        Apart from these, the SOA Record also includes a parameter Serial. This is a number that is automatically generated by our Servers. All Secondary Name Servers cache the Serial Number in the SOA Record, such that when a Serial Number change is detected by Secondary DNS Servers, it updates its Records with the changes. This number is automatically increased by our Servers when changes to the Zone or its Records are made.

      3. Click the Modify Record button to submit your changes.

      Note

      Similarly, to Modify or Delete an SOA Record, simply click the Record Name from the list and then click either the Modify Record or Delete Record button.

    Note

    For the DNS Records you have thus added to be activated, you are required to make modifications to your domain name's Name Servers.

    Additional Information

    Modifying the Name Servers of your domain name