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DNS

The Domain Name Service or Domain Name System (DNS) is used to translate ("Resolve") domain names (which are easy to remember and understand) into IP Addresses, which are unique addresses computers on the internet use to identify each other.

DNS enables you to reach sites on the internet called http://www.apple.com instead of typing in an IP number like 194.168.163.56, and it does this by using "Name Servers" which handle queries from computers on the internet and returns the specific IP address information requested for a particular domain name.

DNS is a huge global network based on 13 root name servers in different geographical locations and stretching out to thousands of individual name servers across the world. DNS is the very heart of the internet, and makes the internet as user friendly as it is today.

Name Servers use 'Zone Files' to store specific information about a domain name, such as the address of name servers or the address of the email servers which handle email for that particular domain. At the start of your zone file you will see a 'SOA' record, 'Start of Authority'. This lists the email contact for the zone (usually a system administrator at the ISP/Registrar), the primary name server for the domain name and technical information such as Time To Live etc. The Time To Live entry defines how long the information is valid for and is not something you need to worry about.

There are several aspects to a zone file, and these are discussed on this page. You can modify the settings in the zone file for your domain (if you are using our name servers) through your Control Panel.

If you modify the zone file for your domain and you make a mistake, your domain name may stop resolving, causing your web site to be unavailable, your email server may be unreachable and any other services you run may stop working.

If you have any doubts, please send the changes you want made to:

BB Online UK Limited
PO Box 2162
Luton
Beds
LU3 2JL
England

Please send this from the registered owner or admin email address.

Alternatively, send a faxed request (on letterheaded paper if possible) to: +44 (0)1582 585057


The Trailing Dot ('yourdomain.dot.yourdomain.dot')

When you edit your Zone File, you must ensure each MX, NS, CNAME or Sub-Domain entry ends with a period ("." - a Full Stop). If there is no period there, our name servers will append your domain name to the end of the entry causing problems. So if you enter an MX record of:

without a trailing period, our nameservers will add yourdomain.co.uk to the end making the entry:

As you can see, this will not work because it is the wrong address.

You don't need to add a trailing dot to the main 'A' record, this should be a straight IP number (the web server for that domain, for instance).

There is an example of a typical Zone File below:


; New Zonefile created upon registration.
; Created : 14-7-2005 at 16:58:54
@               IN      SOA     ns1.bb-online.net. robert.mail.bb-online.net. (
                2004042600 14400 7200 345600 86400 )
                IN      NS      ns1.bb-online.net.
                IN      NS      ns2.bb-online.net.
                IN      NS      brain.bb-online.co.uk.
                IN      MX      10 mail2.bb-online.co.uk.
                IN      MX      20 mail3.bb-online.co.uk.
                IN      A       194.168.163.46

www             IN      CNAME   yourdomain.co.uk.

As you can see, the NS, MX and CNAME records all have trailing periods (.) in the file. As discussed, these are tremendously important. If you overlook this when modifying your zone file your domain name and any services associated with it may stop working.


What is an 'A' record ?

An "A" record, also called an "address" record, binds a domain name to an IP address (e.g. 194.168.163.55). If there is a server on the Internet that is configured to handle traffic for this domain (a web server perhaps), you can enter the name of the domain (like "www.yourdomain.dot") and the IP address of the server (like "194.168.163.55") and almost immediately, anyone surfing to that domain connects to the correct server.

When you edit an 'A' record, you must enter an IP address and not a domain name. As mentioned, the 'A' record binds a domain name to an IP address. For the main 'A' record, this is the IP address that your domain should point to (typically your webserver IP).


What is an 'MX' record ?

"MX" ("Mail eXchanger") records are used to specify what server(s) on the Internet are running e-mail server software that is configured to handle e-mail for your domain. If you want your ISP to handle routing the e-mail for your domain to you, you need to specify the domain name or IP address of your ISP's mail server. In addition, you can prioritise each mail server when you have more than one. Make sure your ISP knows that you're using their servers to route your domain's email, or all your e-mails may be bounced.

You can choose up to 6 Mail Exchange (MX) Servers for your domain. There is no need to define MX prioritys as these will be calculated for you. Simply ensure that the order in which they are entered dictates the priority of the mail server, i.e. the first MX record should be the main (primary) server and any named MX record below are backup servers in their order.

It is common practice to define a sub-domain and tie this to an IP number then use the subdomain (mail1.yourdomain.dot for example) in the MX record rather than enter a straight IP number.

Your MX entries must resolve to an I.P. address and NOT a CNAME, we suggest you avoid using CNAMEs with MX records, as these can cause your domain to stop resolving if they have not been set up correctly within your zone file. It is a safer option to bind your mail host name to an I.P. address in an 'A" record, and then use that host name in your MX record entry(s).

You will see priority numbers for MX records listed in your zone file, the numbers are between 0 and 1000, the lower the number the higher the priority of the MX record.

See the example Zone File below:


; New Zonefile created upon registration.
; Created : 14-7-2005 at 16:58:54
@               IN      SOA     ns1.bb-online.net. robert.mail.bb-online.net. (
                2004042600 14400 7200 345600 86400 )
                IN      NS      ns1.bb-online.net.
                IN      NS      ns2.bb-online.net.
                IN      NS      brain.bb-online.co.uk.
                IN      MX      10 mail2.bb-online.co.uk.
                IN      MX      20 mail3.bb-online.co.uk.
                IN      A       194.168.163.46

www             IN      CNAME   yourdomain.co.uk.


What is a 'CNAME' record ?

"CNAME" records are "Canonical Name" records and create an alias for your domain. You could make an alias like "www" for yourdomain.dot and every reference to "www.yourdomain.dot" would go to "yourdomain.dot", regardless how often your main 'A' records IP address changed.

You can define Unlimited CNAME Aliases for your domain, but we recommend at least one CNAME alias of "www" as typically websites are addressed www.yourdomain.com.

CNAME entries should point to an 'A' record which resolves to an IP address and not another CNAME, if a CNAME entry points to another CNAME entry there is a risk of an infinite loop being created.

Feel free to use a wildcard character like '*' in your zone file:

and this will map ALL subdomains of domain-name.co.uk to your main 'A' record.


What is a subdomain ?

A subdomain allows you to further expand your domain name and add a more specific addresses to your domain. Subdomains take the form:

If you have a website at www.yourdomain.com, and you set up your own mail or FTP server, you could create a subdomain of mail.yourdomain.com or ftp.yourdomain.com (for example) pointing to the IP address of your mail or FTP server.

We do not set a limit on the number of domain names you can create for your domain - you can create unlimited subdomains.


How can i modify my 'A', 'MX' or 'CNAME' records ?

Provided that you have paid for the use of our name servers (ns1.bb-online.net & ns2.bb-online.net) you can request by Email your required zone file changes and we will fulfill your request. You have paid for the use of our name servers if you choose the 'Easy Registration' with unlimited Email and Web forwarding.

If you are using our BB-Online name servers, you can also modify your zone file from your control panel.

Log into your control panel and you will be able to define the name servers for your domain and you also have full control over your zone file, you can create sub-domains, set MX records and pretty much anything else all through your control panel which is available 24 hours a day all year round.


What is an NS record ?

An NS record records the name servers you specify for your domain. If you want to change the name servers for your domain, don't do it directly through the zone file, use the 'Update DNS (Nameservers) & Contact Info' link in the control panel.

The name servers which are authoritive for your domain are listed in the NS records of the zone file for your domain, these should be bb-onlines nameservers and you should leave them as their default unless you know exactly what you are doing. Changing these may cause your domain not to resolve, and if you have a web site for your domain, this may become unavailable until the name servers are correct.


Propagation: How long before my changes take effect ?

Once you have made changes to you Zone File, these changes need to propagate across the many different servers on the internet before your the new information about your domain is seen by everyone. Sometimes these changes can take effect in a relatively short time span, but it may take anywhere between 24 and 72 hours before the changes have been fully propagated.

Many name servers cache information on a 24 hour basis, so when a change is made to your zone file the name servers still give out the old cached information instead of the new information. We do not have any control over how ISPs on the internet operate, so please ensure you allow time for the changes you make to propagate (72 hours is the upper limit for propagation of changes made).