A DNS query (also known as a DNS request) is a demand for information sent from a user's computer (DNS client) to a DNS server. In most cases a DNS request is sent, to ask for the IP address associated with a domain name. An attempt to reach a domain, is actually a DNS client querying the DNS servers to get the IP address, related to that domain.
In general, there are two ways of resolving a host or a domain name to an IP address, using the domain name system – a Recursive DNS query and a non-Recursive DNS query.
The Recursive DNS query is, when a DNS client directly gets the IP address of a domain, by asking the name server system to perform the complete translation.
The non-Recursive DNS query is, when a DNS client contacts the name servers, one by one, until it finds the server, containing the needed information.
The process behind Recursive DNS queries, can be explained by the following example:
1. A user opens up his favorite browser and enters https://www.somedomain.com in the address bar. His computer does not know the IP address for www.somedomain.com, so it sends a request to the user’s DNS resolver.
2. The resolver does not know the IP address for www.somedomain.com, so it will query one of the root DNS servers.
3. The root servers know the locations of all the TLDs, such as .com, they do not know the IP of www.somedomain.com, so they return the location of the .com servers.
4. Once the query reaches the .com TLD servers, it will find the Authoritative DNS server of www.somedomain.com and will reply to the resolver with that server.
5. The resolver will send a query to the Authoritative DNS server of the domain and will resolve it.
6. The Authoritative DNS server of the domain will check within its database and will find an entry for www.somedomain.com, which has an IP address.
7. Finally the resolver will know the IP address for www.somedomain.com and will send the result to the user's computer.
The process behind non-Recursive DNS queries, follows the same procedure, but the DNS client (the machine from which the user tries to resolve the domain) will have to find the authoritative DNS server for the domain, by itself.
The DNS client will have to ask by itself, first the root servers, then the TLD servers and finally the Authoritative DNS server to be able to resolve the domain.
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The DNS query is crucial to the functioning of the Internet. Without DNS queries, users would have to remember the IP addresses of websites they want to visit, which is impractical. DNS queries allow users to easily access websites using their domain names, making the Internet more user-friendly. Additionally, DNS queries help distribute web traffic across multiple servers, which improves website performance and reduces downtime.
A DNS query is structured into several parts to facilitate the process of domain name resolution. The core components of a DNS query include the header, question, answer, authority, and additional sections. The header section contains general information about the query, such as the transaction ID and flags indicating the query type (e.g., recursive, non-recursive). The question section specifies the domain name being queried and the type of record sought (e.g., A, MX, etc). Following the question, the answer section provides the requested information if available, while the authority section lists authoritative name servers for the queried domain. Lastly, the additional section can contain extra information helpful in the query process. Together, these sections allow DNS clients and servers to communicate efficiently, translating human-friendly domain names into machine-understandable IP addresses.
Question: Can DNS queries be encrypted?
Answer: Yes, DNS queries can be encrypted using protocols such as DNS over HTTPS (DoH) and DNS over TLS (DoT).
Question: What happens if a DNS query fails?
Answer: If a DNS query fails, the client will not be able to connect to the website associated with the domain name. DNS queries fail for different reasons, such as server downtime, network connectivity issues, or incorrect DNS settings.
Question: Can DNS queries be intercepted or manipulated?
Answer: Yes, attackers can intercept or manipulate DNS queries using techniques such as DNS spoofing or DNS hijacking. As a result, the user can be redirected to a fake website or has their personal information stolen.
Question: Are DNS queries case sensitive?
Answer: DNS queries are not case sensitive. The domain name system treats 'Example.com' and 'example.com' as identical. This case insensitivity is defined in the DNS protocol standards, ensuring that domain lookups are consistent regardless of the case used in the query.