Abu Zar Mishwani
The Domain Name System (DNS) is an integral part of the modern internet. It serves as an organizational backbone, enabling users to access websites and other online resources easily. Despite its importance, many users are unaware of the inner workings of DNS and how it affects their online experience.
In this article, we’ll provide an in-depth look at DNS, explore its history, and discuss why it is so important to the modern internet.
What is DNS?
DNS stands for Domain Name System. It is a system of computers, servers, and databases that turns a human-readable website address into an IP address that is used by computers to connect to websites. When you type a website address into your browser, the DNS looks up the address and translates it into the IP address of the server hosting the website. In this way, DNS acts like a phone directory, allowing your computer to look up the right server for the website you want to visit.
DNS works by using a hierarchical system of DNS servers. At the top of the hierarchy is the root server, which is responsible for delegating requests to the other DNS servers. Requests are then sent to the authoritative nameservers responsible for the domain name in the request. The authoritative nameserver looks up the IP address associated with the domain name and sends it back to the requesting computer. The requesting computer can then use the IP address to connect to the website.
DNS is essential for the internet to function properly. Without it, computers wouldn’t be able to find the correct website when a user types in a website address. DNS also allows for easy website management as changes to websites can be made through the DNS servers instead of having to update each computer directly.
This system is beneficial because it allows people to easily access websites without having to remember the corresponding IP address.
For example, instead of remembering the IP address 123.456.789.000 to access a website, you can simply type in the domain name e.g., www.example.com, and DNS will automatically translate it into the correct IP address. This makes it easier for users to access websites and other resources on the internet.
How Does DNS Work?
DNS is essentially a phonebook for the internet. It’s a distributed database system that translates domain names, such as www.example.com, into IP addresses, such as 172.217.30.206. Without DNS, it would be impossible for users to navigate the internet easily.
For example:
- When a user types
example.cominto a web browser, the query is sent to a DNS recursive resolver. - The resolver then queries a DNS root nameserver to find the address of the appropriate Top Level Domain server (such as
.comor.net). - The root server provides the address of the TLD server, which stores the data for the requested domain.
- The resolver then requests information from the TLD server.
- The TLD server responds with the IP address of the domain’s nameserver.
- The recursive resolver then queries the domain’s nameserver.
- The nameserver provides the IP address for the requested domain and sends it back to the resolver.
- The resolver then responds with the IP address to the web browser.
- The browser then makes an
HTTPrequest to the IP address. - The server at that IP transmits the webpage to the browser to be displayed.
The process of obtaining information from the various servers happens very quickly and is usually not noticed by the user. The system only needs a moment to query the different servers and receive the data.
When someone outside of a domain asks a DNS server for information about a name or address inside the domain, the server will provide an authoritative answer to the inquiry.
When a server receives a request for a name or address that lies outside of its domain, it will typically pass on the query to another server, typically one managed by its Internet Service Provider (ISP). This allows the server to access the requested information from a different location.
Types Of DNS Servers
DNS resolution involves four types of servers. A query will go through them in a specific order. These servers provide either the domain name being searched for or refer the query to other name servers.
#1. Recursive Server
The recursive server acts as a gateway for users, allowing them to access web pages and other online services. It takes DNS queries from applications such as web browsers and either provide the answer from its cache or seeks out the next-level server if it does not have the answer. Querying may require multiple steps before returning an answer to the client.
#2. Root Name Server
The root name server is the first place a recursive server sends a query if it doesn’t have the answer stored in its cache. It is a directory of all the servers that have the information required by the query. The Internet Corporation for Assigned Names and Numbers (ICANN) is responsible for overseeing these servers, with a special branch called the Internet Assigned Numbers Authority taking charge.
#3. TLD Server
A Top Level Domain (TLD) server is a DNS server responsible for resolving domain names into IP addresses for the highest-level domains, such as .com, .net, and .org. The TLD server stores the IP addresses of all the nameservers for the domains it serves. This allows it to determine which nameserver to look up when requesting a domain name.
#4. Authoritative Nameserver
An authoritative nameserver is a DNS server that is authoritative for a particular domain or subdomain. This means it is responsible for providing the DNS records for a domain, such as the A, MX, and CNAME records. Authoritative nameservers are also responsible for processing DNS queries. They are the final source of truth for a domain’s DNS records and will answer queries with the most up-to-date records that they have. When a DNS query is made, the authoritative nameserver is responsible for providing the answer. They are the authoritative source of DNS records and are responsible for propagating changes to the DNS records in the zone.
The recursive server acts as a go-between, asking queries on behalf of the user and forwarding the answers to them. The root and TLD servers are responsible for directing the query to the appropriate authoritative server, which is the one that answers the user’s query.
Types of DNS Queries
Several different types of DNS queries can be made depending on the requested information. These queries can be divided into three main categories:
#1. Recursive DNS Query
A recursive DNS query is a type of query in which a DNS resolver requests information from a DNS server and expects a complete answer to the query. This type of query is used by most DNS clients on the Internet to locate the IP address of a domain name. The DNS server is responsible for resolving the query by either returning the answer from its own cache or by querying other DNS servers on behalf of the client. In a recursive query, the DNS server keeps querying other DNS servers until it finds the answer or reaches a point where it can no longer query any other servers. Once the DNS server has the answer, it sends it back to the client.
#2. Iterative DNS Query
An iterative DNS query is a type of query in which a DNS client asks for a specific type of record from a DNS server. The server will then attempt to resolve the query and return the requested record. If the server cannot resolve the query, it will return a referral to another DNS server that can provide more information. This process will continue until the DNS client receives the desired record or until the server is unable to resolve the query. Iterative queries are the most common type of DNS query and are used by most DNS clients when they are looking to resolve a domain name or IP address.
#3. Non-recursive Query
A non-recursive query is a type of DNS query that requires the DNS server to respond with the data it has readily available in its cache rather than initiating a recursive query to find the answer. Non-recursive queries are used to quickly retrieve data from a DNS server without having to wait for a recursive query to return. This type of query is used to ask the DNS server to return data stored in its cache, such as a DNS record, without having to initiate a recursive query. This is useful when a DNS server needs to respond quickly to a client’s query, such as in a web page request.
When a client wants to resolve a domain name, it sends a recursive query to the recursive resolver. The resolver then makes a series of iterative queries that direct it to the next step in the process. This continues until the query reaches the authoritative server, which can provide the answer. If the resolver knows the answer can be found there, it sends a non-recursive query to retrieve the information. The data is then stored on the resolver so that a nonrecursive query can be used to access it in the future, thus providing quick access to the same domain name.
Common DNS records
DNS records provide the information requested by a query from a client or application. Depending on the nature of the query, different records are needed. The A record is an essential part of the process, as it provides the basic details needed for the query to be successful.
There are several sorts of DNS records, each serving a specific function in indicating how a query should be handled. The following are common DNS records:
1. A Record (Address Record): An A Record is a type of DNS record that points a domain name or a subdomain name to an IP address. A Records determines the IP address associated with a domain name. When a user enters a domain name into a web browser, the browser will first query the DNS system to resolve the domain name to an IP address.
2. CNAME Record (Canonical Name Record): A CNAME record is a type of DNS record used to point a domain name or a subdomain name to another domain name. A CNAME record is used when a domain needs to point to another domain name, not an IP address. CNAME records are commonly used to point a www subdomain to a root domain, such as pointing www.example.com to example.com.
3. MX Record (Mail Exchange Record): An MX record is a type of DNS record used to specify which mail server is responsible for accepting emails for a particular domain name. MX records are used to help route emails to the correct mail server.
4. TXT Record (Text Record): A TXT record is a type of DNS record used to store arbitrary text data. TXT records are commonly used to store SPF information, which is used to verify the identity of a domain for email purposes.
5. NS Record (Name Server Record): An NS record is a type of DNS record that is used to specify which name servers are authoritative for a particular domain name. An NS record is used to specify which name servers are responsible for answering queries for a particular domain name.
DNS Caching
DNS caching is a process by which DNS responses are stored in a local cache on a computer or network device. When a user visits a website, the DNS server is queried to find the IP address associated with the domain name. The DNS server then returns the IP address to the user’s computer and stores the IP address in a cache. The next time the user visits the website, the IP address is retrieved from the DNS cache, reducing the time it takes for a DNS query to be answered.
This process helps reduce the amount of traffic sent across the internet, which helps websites load faster for users. It also helps reduce the load on DNS servers, as they don’t have to answer the same queries multiple times. In addition, it helps protect users from DNS spoofing attacks, which are attempts by malicious actors to redirect users to malicious websites by providing them with incorrect IP addresses.
There are several places where DNS data can be cached. Common examples include the following:
#1. Browser:
Web browsers such as Internet Explorer, Firefox, and Chrome will cache DNS records for future reference. When a user enters a website URL into their browser, the browser will check its cache for the DNS record associated with the URL. If it finds the record, it will use that information to connect to the website instead of having to look up the record again.
#2. Operating System:
Operating systems such as Windows, macOS, and Linux will also cache DNS records. This allows them to look up the domain associated with an IP address quickly. It also prevents programs from having to look up the same DNS record multiple times, saving time and resources.
#3. DNS Server:
DNS servers also cache DNS records. This allows them to respond quickly to DNS requests without having to look up the same record multiple times. DNS servers are designed to remember records for a certain amount of time before they are automatically removed from the cache.
#4. Routers:
Routers may also cache DNS records. This allows them to respond quickly to DNS requests from the local network. This can improve performance for users on the local network, as the router does not have to look up the same record multiple times.