A quick introduction to DNS and how it works

Domain Name Servers are the backbone of the modern day internet.

So how does it work? Every computer on the internet is given a specific number called an IP address that can uniquely identify that computer on a network. For example letshost.ie will resolve to 78.137.164.40 and google.ie resolves to 209.85.143.104.

DNS effectively acts as the phone directory of the internet mapping computer-readable IP addresses to human-readable domain names. One could easily argue that the Internet would not have reached such levels of popularity if websites advertised on the internet were of the form http://123.321.12.23. This is just too hard for humans to remember.

Nameservers hold a lot of information regarding a specific domain such as where to route a connection so that the webpage is displayed or where to route email.

A domains “A” record governs where a domains website can be found. An A record is entered as an IP address so that when a nameserver is queried it looks down through the “phone book” until it finds the domain and and then redirects the user to the appropriate IP address. The same is true for the MX (mail exchange) record which directs a domains email.

Lets take the domain Letshost.ie as an example…
Letshost.ie uses the nameservers ns1.dnsireland.com & ns2.dnsireland.com
When you type letshost.ie in to your internet browser the .ie of TLD (top level domain) directs the connection the .ie root nameservers (IEDR). The root nameservers show that letshost.ie is currently using the following nameservers:
ns1.dnsireland.com & ns2.dnsireland.com

These nameservers contain the A and MX records (possibly alot more) for letshost.ie
The A record points to where the website is being hosted, 78.137.164.40 in this case.
The MX record routes email to a specific server antispam.letshost.ie which has an IP of 78.137.164.25

As you can see the DNS zone record for letshost.ie can direct traffic to differnt locations depending where the service is located. A subdomain bogota.lethost.ie can be set up and pointed to a server in Bogota to serve Letshosts customers in Colombia for example.

Changes to a domains nameservers will not happen instantly. These changes take time to propagate out to all the internets routers. The algorithms that are used by routers to direct internet traffic pass these changes of IP addresses to each other. It can take up 24hours for a domains to fully propagate throughout the internet.