DNS (Domain Name System) is an essential technology for using the Internet on a daily basis. Without DNS, you won’t be able to access email or browse websites. However, many people may not have an overview of them.
Therefore, in this article, we will explain the functions and mechanisms of DNS, as well as introduce an example of how it is used. We will also explain security-related incidents that have occurred related to DNS, so please use this as a reference.
Functions of DNS (Domain Name System)
DNS
is a system that connects domain names and IP
addresses
. The premise is that a domain is information that corresponds to an address on the Internet. An IP address is specific information given to each device, and may also refer to an address on the Internet, but there is a big difference between the two.
In the case of an IP address, it is simply a list of numbers, so humans and users cannot determine what kind of website it is when viewing it. On the other hand, a domain is a more easily understood version of these numbers.
For example, when viewing a particular website from a web browser, it is necessary to obtain the IP address where the website is managed. However, since viewers search using domains, it is necessary to link domains and IP addresses.
By using DNS, you can convert domain names to IP addresses. This allows users to access your website instantly.
There are several types of DNS. A typical DNS is “Public DNS”. Public DNS is a DNS that is open to the public on the Internet and can be used freely by anyone. There are also multiple types of public DNS, and Google Public DNS’s “8.8.8.8” is one of the most famous. This DNS is known for its extremely fast response speed and is also characterized by high security.
We will also explain about “caching servers” and “authoritative servers” as they relate to DNS.
cache server
A
cache
server is a function that allows file information accessed by users in the past to be saved on a web
server
. Since it is stored on the web server, there is no need to create a new file even if a similar request is sent from a web browser. Users can access your website faster than before because it takes less time to create new files.
authoritative server
An authoritative server is a server that has the right (authority) to publish specific information on the Internet. For example, suppose a domain called “example.com” exists. In this case, the authoritative server has the authority to publish hosts such as “www.example.com” and “https://example.com” of example.com.
As mentioned above, an authoritative server is a server that stores content that can be published, so it is also called a content server.
How DNS (Domain Name System) works
So far, we have explained the functions of DNS. Here, we will introduce how DNS works. First, when users try to access a website, they type the website’s URL into their web browser.
Next, the user’s device begins acquiring an IP address from the DNS cache server. At this point, if the IP address is stored in the cache server, the IP address will be returned and the website will be displayed.
On the other hand, there are cases where the IP address is not stored in the DNS cache server. In that case, the web browser will begin searching for which DNS owns the IP address. Then, as soon as the DNS that holds the IP address is found, the IP address is returned to the web browser and the website is displayed.
An example of a scene where DNS (Domain Name System) is used
So far, we have explained how DNS works. From here, we will introduce an example of a scene where DNS is used.
- Send email
- Browsing websites
Let’s look at each in turn.
Send email
Basically, a server called a mail server is used to send email. A mail server is a server (system) for sending and receiving emails. The basic mechanism for sending an email until it reaches the recipient is to first send the email to the recipient from your own PC.
Then, the email is delivered to your subscribed email server, and then the destination IP address is determined through the DNS server. By obtaining an IP address from this DNS, the mail server with which we have a contract will be able to send mail through the destination mail server.
The above sequence of steps is the general flow of email sending and receiving using DNS. Therefore, the mail server plays the role of a relay point, and the DNS has the role of calculating the destination after relaying.
Browsing websites
As explained in this article, DNS is also used to browse websites. The role of DNS is to specify IP addresses for requests sent from web browsers.
The specific mechanism for displaying a website is that the user enters the domain they wish to display into their web browser. The web browser then requests IP address information from the DNS server. Essential
The requested DNS server replies with the specified IP address, and the web browser requests the obtained IP address from the web server. Then, the web server displays the website on the user’s web browser based on the requested IP address information.
As mentioned above, browsing a website is characterized by three things working together: the web browser, DNS server, and web server.
What is a DNS record?
So far, we have explained about DNS. Next, let’s understand what is called a DNS record. A DNS record is a single line of text listed in a zone file mapping table. Also, a zone file refers to a correspondence table between IP addresses and domain names.
Here are some typical DNS records.
- A (Address): Associates an IP address with a host name + domain name
- CNAME (Canonical NAME): Transfer to another host name + domain name
- NS (Name Server): Leaves processing to a different DNS server
- MX (Mail Exchange): Allows you to use email with host name + domain name
- TXT (TEXT): Something that allows authentication
In addition to the above, there are other DNS records as well. However, when it comes to DNS records, there is no problem as long as you know the above five outlines first.
DNS (Domain Name System) related incidents
So far, we have explained about DNS and DNS records. DNS is a very important system in today’s Internet-centric world. However, there have been major incidents related to DNS in the past.
For example, in 2016, websites and services such as the Wall Street Journal, Twitter, and Netflix went down all at once. This is due to a DDos attack (Distributed Denial of Service attack). Simply put, a DDoS attack is an attack that aims to take down a server or service by placing a large amount of load on it. If the service is suspended, you risk losing trust from users.
Additionally, the attack continued for over four hours. Since this incident, the importance of creating a stronger security system for DNS, which plays an important role on the Internet, has been reconsidered.
summary
In this article, we explained about DNS (Domain Name System). DNS functions as a translator when connecting domain names and IP addresses, and is used when viewing websites and emails.
With DNS, a name is assigned to each domain name and functions. First of all, why not read this article repeatedly until you understand the mechanism of DNS in detail?