In the late 90s or early 2000s, do you remember that people used to use long directories to save the phone numbers of friends and family? Well, we don’t do that anymore, thanks to smartphones.
You can imagine a Domain Name System (DNS) as a virtual directory of the Internet. It is a huge database that consists of the names of billions of websites. You must be familiar with the concept of IP addresses by now. We recommend you go through this brief introduction to IP address if you’re not aware of this concept.
Note: If you haven’t read the previous blog of our CCNA 200-301 series, I highly recommend you do so.
In this blog, we will learn about the Domain Name System (DNS) and how it works. We will also learn about the types of Domain Name Systems.
Let us begin learning about DNS!
The Domain Name System popularly referred to as DNS is a service that translates the website name (domain name) of a website to its IP address. It is a naming database that consists of the names of various domains that are translated into IP addresses.
For example, if you look up “Facebook.com” on a web browser, the DNS present in the server would internally look for the match of this domain name system with its IP address. The IP address of Facebook ranges between 22.214.171.124 to 126.96.36.199.
Why Is There a Need for Domain Name System (DNS)?
Before the Domain Name System was invented, people actually had to remember the IP addresses of various websites. But with the exponential increase in the number of websites, there has to be a system to keep track of them.
This is when the Domain Name System (DNS) was invented. It made everything easier. Now, people did not have to remember the IP address of a website. It is also relatively easier to remember the names of websites than the IP addresses.
It is very important for you to know that the Internet does not understand the Domain Names of websites, it can only understand the IP addresses. As you know, IP addresses are very important to allow computers to communicate over the Internet.
Therefore, the Domain Name System is a huge database created for human ease. The Internet does not understand it.
Note: The DNS protocol works in the Application Layer.
How Does the Domain Name System (DNS) Work?
When a user enters a website name in the web browser, its request is accepted only after the domain name is successfully translated into its IP address. This whole process of conversion and mapping the IP addresses is called DNS resolution.
Let us learn about this process of DNS resolution in detail. Here are the various steps involved in this process:
1. DNS query is initiated:
First of all, the user enters the domain name or the website name in a web browser. This initiated a DNS query through a DNS client in a web browser.
2. Query reaches recursive resolver:
This DNS query then reaches a recursive DNS server also known as the recursive resolver. Typically, Internet Service Providers (ISPs) such as Jio, Verizon, Vi, BSNL, etc. operate a recursive resolver. Its function is to decode the IP address with the help of other DNS servers if needed.
3. Recursive resolver approaches other servers:
In case, the recursive resolver cannot crack the IP address of a website, it then reaches out to other servers in the following order:
- DNS root name servers
- Top-Level Domain (TLD) name servers
- Authoritative name servers
These servers work together until they find out the IP address of the respective website. This information is then passed on to the recursive resolver. DNS and TLD only redirect the DNS queries. Authoritative servers mainly resolve the query.
4. DNS caching:
The recursive server then caches or stores the domain name containing the IP address. This creates a memory in the recursive resolver and it does not have to approach other servers if another user raises the same request!
5. Chances of error:
Sometimes, even the authoritative servers cannot find the IP address of a website. In such a case, an error is returned to the user.
Can you believe that all of this process happens in milliseconds that a user cannot even recognize? This is the beauty of the Domain Name System (DNS).
There are mainly three types of DNS servers are as follows:
- Primary servers
- Secondary servers
- Caching servers
1. Primary Servers:
- It is the authoritative server where the DNS query is resolved in the recursive resolver.
- All the important tasks such as creating subdomains and other administrative tasks are performed by these servers.
- In case any chances are supposed to be made in the zone files, the primary servers need to be modified for the same.
- Only one primary server is assigned to each zone.
2. Secondary Servers:
- All the backup DNS servers are secondary servers.
- A zone transfer occurs in which the primary servers transfer the files to the secondary servers.
- The secondary server performs the following functions:
- Load balancing
- Fault tolerance
- Traffic reduction and mitigation
3. Caching Servers:
- The caching servers are also called caching-only servers.
- When a DNS query reaches the caching servers, these servers provide the stored or cached-query service.
- These servers perform the DNS queries, cache the answers, and then return the query to the DNS client.
- Caching servers do not maintain any zone files.
This marks the end of our Domain Name System (DNS) blog. It is one of the most important concepts covered in the Cisco Certified Network Associate (CCNA) exam.
You can also read about the DHCP here. It is also one of the most important protocols used in networking and is associated with IP addressing. Make sure that you go through our complete CCNA blog series to have a better understanding of these concepts.
Stay tuned for the upcoming blog of our CCNA 200-301 series.