Knowledgebase

The DNS (domain name system) Editing tool found in your account's cPanel is a powerful system for editing your domain DNS entries.

This tool will edit the live zone file (the file that stores your DNS values) for your domain name, which starts the propagation of your changes immediately. This system also allows you to set up custom TTLs and sub-domains with only a few small changes.

With a system as powerful as this, it is important that the small changes you make are fully understood, as a bad zone file can not only take your domain or email offline, but keep it offline from 30 minutes to several days!

Brief explanation of DNS

DNS is the system used on the internet to find the IP and services associated with a particular domain name.

When someone visits a website or sends an email, your PC needs to find out what the IP of the server the website is on or which server to send the email to. So, it finds out which computer has the zone file for that domain name, and then they ask those nameservers for the IP address.

If servers had to keep doing these same lookups over and over again they would become quite slow. So instead, they store the answer for a while so it can be used again the next time someone enters the same domain name in a web browser or sends an email.

This process of storing the answer is called "caching" and the length of time the information is cached depends on a DNS setting called the "minimum" or "TTL" (time to live) which is found in a domain name's SOA (start of authority) record.

The effect this has on making changes to a domain name's DNS (like changing an IP address) is that the change will not be used until the old address information is removed from the cache.

The process of waiting for old information to be removed from the cache so that the new information is seen by everyone on the internet is called propagation and will depend on the minimum/TTL setting.

Explanation of a DNS record

A DNS record is a small instruction that can be requested by another computer or internet server, it consists of 4 elements, the domain, TTL, Record Type and Value.

The domain is the internet zone you wish this record to apply to, the domain can only be set to either the domain or sub-domains of that domain. For example, the zone file for hostingireland.ie could not set the domain in a DNS entry in its own zone file to google.com, but it can set it to a sub-domain such as orders.hostingireland.ie.

Regarding the domain, there is a much overlooked item, referred to as a termin ating dot, which tells the server that this is the end of the value, if the domain does not end with a . the server will automatically place .domain.com. on the end of the value. For example, in the hostingireland.ie zone file I enter the domain value as 'www' the server will automatically place '.hostingireland.ie.' on the end, so the full value is 'www.hostingireland.ie.'. This is how it should be used, however, an example of when this can be used incorrectly is if I fill in the domain as 'hostingireland.ie' then the server will change that to 'hostingireland.ie.hostingireland.ie.' or if I fill the domain as 'www.' The server will not update that, and so it will not apply to any domain.

The TTL is a value for the period of time that caching servers should keep this record, in seconds. It should never be lower than 3600 (30 minutes), other than in extreme circumstances.

The Record Type can be set to various values; they are listed and explained below (the most commonly used values are at the top):

The Value of a DNS entry can have either 1 or 2 elements but for the most part they will have 1, the value can vary depending on the record type value. Here is the value layout for the 3 most common record types above:

A: The IP (with no termin ating dot) that the domain value should resolve to.

CNAME: The domain that the domain value should be an alias of.

MX: 2 values, the first value is the preference of the record, the second is the address of the mail server and should be a CNAME rather than an IP.

The preference of an MX record can be set to any value equal to or greater than zero, the server will attempt to deliver mail to the lowest number preference first, and if that fails, move to the next highest preference.

Finding the Editor

Login to your hosting ireland client area at http://clients.hostingireland.ie then click on 'Manage Domains' click on 'View Details' of the domain whos DNS you want to edit, then click on 'DNS Management' at the bottom of the page, you will then be presented with all the current DNS records for your domain name.

Overview of the Editor

In figure 1 you can see a snapshot of an existing Zone file, several areas have been labeled and we will review the purpose and description of each of these now.

Figure 1

A:

The domain name this zone file is active for and the TTL (Time to live) for the zone file.

B:

1) The first field is the master nameserver for this domain name.

2) The serial number doesn't have to be a date, however, whenever a change to the zone file on the master DNS server is changed, the serial number must be increased by some value. That way, any caching server(s) will know that an update has been made, and they'll do a zone transfer to get the newest copy of the zone file

3) Refresh is the time the server caching this record should keep it cached for, before it will refresh the file.

4) Expire is the maximum amount of time the caching server should keep these values, even if it has been unable to refresh them.

5) Minimum TTL is similar to the Refresh value, as in, this is the time we expect the caching server to retrieve new information from the domains nameservers.

C) This is a DNS entry in your Zone file, which specifies the primary, secondary and even tertiary nameservers for this domain.

1) Domain name, this is the domain that is to be affected by the following values.

2) TTL, this is how long the caching server should cache this DNS entry.

3) IN, this is a static value, and is short for internet, meaning this is a DNS entry for the internet.

4) This specifies the record type.

5) Value, the actual value to be stored for this entry.

Below the existing DNS entries are the list of empty entries, which can be used to create a new DNS entry. See part A in figure 2.

Figure2

A new record is the same as an existing DNS record, it simply has no values yet.

The first field will be filled with the domain value, which can be either the domain, or a sub-domain.

The second field is the TTL for your new value.

The third field is the record type.

Once you choose a record type, the correct amount of input boxes will appear for the value of the entry on the right hand side, see the two example images below.

Figure 3

It will also prompt you with the expected input, which should be deleted before you make your own entry.

Conclusion & Further reading

So we have fully investigated the DNS editor now, and hopefully you are able to understand and make changes to your own DNS at this point.

If you are still eager for more information on DNS workings, you can find much more information on dns.net, a good place to start on that site, is here: http://www.dns.net/dnsrd/