How to Make an IP Address Fully Qualified
For the Internet to be able provide the IP address of the exact server you need to connect to in order to visit the website you want, you need to provide a complete website address. This is called a Fully Qualified Domain Name (FQDN).
An FQDN is comprised of three parts:
The domain name
The extension, which is also known as the Top-Level Domain (TLD)
For example, the domain www.dummies.com has the following components:
The hostname is www.
The domain name is dummies.
The TLD is .com.
When searching for a website your computer reads the address from right to left — and here’s why:
The foundations on which the Internet is built are a set of servers called the Internet Root Name Servers. There are 13 root nameservers and they have a critically important job: Root nameservers deliver one fairly small file to any computer that requests it.
The Root Zone File contains the IP addresses of another set of servers called the TLD nameservers. There are a number of types of TLD, the most common of which are the following:
Country-Code Top-Level Domains (ccTLD): These are comprised of two letters preceded by a dot and they are internationally recognized as the code for a specific country. These were set up by the International Organization for Standardization (ISO) and are known as the ISO 3166 codes.
Internationalized Top-Level Domains (IDN TLD): These are ccTLDs in non-Latin character sets.
Generic Top-Level Domains (gTLD): These domains usually include three letters preceded by the dot (for example, .com, .org, and .net), but may contain more.
Each separate TLD has its own “Authoritative Nameserver” with its own unique IP address. The simplest definition of a nameserver is a server that holds a directory of domain names mapped to the IP addresses of the servers those domain names reside on.
The term Authoritative Nameserver defines a server as the one that is kept the most up-to-date. You can have secondary nameservers, which hold a copy of the records from the Authoritative Nameservers, but if there are any discrepancies, the authoritative server is treated as the correct one. Authority is defined by a Start of Authority (SOA) record.
So, for example, the Authoritative Nameserver for the TLD .com holds a list of all the .com domain names and their IP addresses, the nameserver for the TLD .org holds a list of all the .org domain names, and so on.
When you type an FQDN into your browser — for example, www.google.com — your browser goes to a DNS server and asks if it knows the IP address of www.google.com. If the DNS server does not know the address then your browser requests a recursive search, which means the DNS server must search every resource it can for the answer and either come back with the address or a failure message.
The DNS server then starts an iterative search, which goes a little something like this:
First it goes to a Root Name Server and asks, “Do you know where I can find www.google.com? If not, can you suggest where I should look?” The Root Name Server says, “No, but I know where the .com server is; go ask the .com server.” It then supplies the DNS server with the IP address of the .com server.
The DNS server then goes to the .com nameserver and says, “Do you know where I can find www.google.com? If not, can you suggest where I should look?” The .com server replies, “No, but I know where the google.com server is.” It then sends the DNS server to the Authoritative Nameserver for google.com.
When the DNS server queries the google.com nameserver, the DNS server first checks that the nameserver is authoritative for the domain, and, if it is, asks, “Do you know where I can find www.google.com? If not, can you suggest where I should look?” The google.com nameserver checks its zone record for that hostname and either returns an IP address or tells the DNS server the hostname does not exist.
To make the name fully qualified it requires another part before the domain name, such as www., which is the hostname.
Because of the way the DNS works, this extra element, the hostname, is important. In most cases, by default, if you type a domain name into a browser and do not include a hostname, it will assume a default hostname of www.
The Authoritative Nameserver for the domain holds an index of all the hostnames configured for that domain and the IP addresses where those hostnames are found, called the DNS Zone File. The way the majority of websites are configured, the server that actually houses the domain name also acts as the nameserver.
This is just for simplicity and cost purposes, but it is not the most advisable way to do things.
Resilience is the key to the continued functioning of the Internet and so, all the way through this process, multiple servers are actually in play. If one or two were to go down for some reason, plenty would remain that your browser could find.
At any stage of the iterative search if the DNS server exhausts the possible IP addresses it is provided, and then it returns an error and your browser displays that error message. The sheer size of the infrastructure behind the Internet Root Nameservers and TLD servers makes it unlikely that your browser or the DNS server will ever fail to find one of them.
Normally if an error message appears, it is either because the Authoritative Nameserver for the domain could not be found or because the IP address the Authoritative Nameserver said the website is at is incorrect.