What is DNS and how does it work?

DNS is a fundamental component of the internet’s infrastructure. It’s like a phonebook for the Internet. Without it, reaching your desired online destination would be a tedious and time-consuming process of trial and error, dialing random digits in the hope of stumbling upon the right connection. 

DNS eliminates this frustration by providing a reliable directory that instantly translates the website names we know into the precise Internet addresses required for seamless navigation. By efficiently mapping domain names to their corresponding IP addresses, DNS plays a crucial role in enabling seamless and user-friendly Internet communication.

In this guide, we’ll be covering:

• What is DNS?
• How does DNS work?
• Why is DNS important?
• What are the different types of DNS servers and queries?
• What’s the difference between an authoritative DNS server and a recursive DNS resolver?
• What is DNS caching and how does it impact web performance?
• What attacks is DNS prone to?
• How can you prevent cyber attacks on DNS?
• Final thoughts

What is DNS?

DNS stands for Domain Name System. It’s a hierarchical and distributed system that translates human-readable domain names, such as www.example.com, into machine-readable IP addresses, such as 192.0.2.1. This allows devices to locate and communicate with each other using domain names. 

How does DNS work?

DNS works through a hierarchical and distributed architecture involving various components and processes. Here’s a simplified explanation of how DNS functions:

1. DNS resolution request: when a user enters a domain name, such as www.example.com, into a web browser, a DNS resolution request is initiated. The request is sent to a DNS resolver, which is typically provided by the user’s Internet Service Provider (ISP).
2. Recursive DNS resolution: the DNS resolver receives the resolution request and acts as an intermediary between the user’s device and the DNS infrastructure. If the resolver doesn’t have the requested domain name information cached, it performs a recursive resolution process.
3. Querying DNS servers: the DNS resolver sends a query to the root DNS servers, asking for the authoritative DNS server responsible for the top-level domain (TLD) of the requested domain name, such as “.com”. 
4. Resolving the TLD: the root DNS servers respond with the IP address of the TLD’s authoritative DNS server. The resolver then sends a query to the TLD’s authoritative server, asking for the authoritative DNS server responsible for the next level domain, such as “example.com”.
5. Resolving the domain name: the TLD’s authoritative DNS server responds to the resolver with the IP address of the authoritative DNS server for the specific domain, such as “www.example.com”. The resolver then sends a query to the domain’s authoritative server.
6. Retrieving the IP address: the authoritative DNS server for the domain returns the IP address associated with the requested domain name, such as “www.example.com” to the resolver.
7. Caching and response: the resolver caches the IP address received from the authoritative server to speed up future resolutions for the same domain. It then sends the IP address back to the user’s device, allowing the application to establish a connection with the appropriate server hosting the requested content.
8. Communication with the web server: with the IP address obtained, the user’s device can now communicate directly with the web server associated with the requested domain. This enables the retrieval of the desired web content or any other internet-based service.

Why is DNS important? 

DNS is crucial for the functioning of the Internet due to the following reasons:

• Human-friendly naming: DNS assigns easy-to-remember domain names to Internet resources, allowing users to access websites and services using familiar names instead of complex IP addresses.
• IP address resolution: DNS resolves domain names to their corresponding IP addresses, enabling devices to locate and connect to the correct servers hosting the desired content or services.
• Scalability and redundancy: DNS’s hierarchical and distributed structure ensures scalability and redundancy, improving Internet reliability and performance.
• Loading balancing and traffic management: DNS enables traffic distribution across multiple servers, balancing the load and optimizing resource usage and ensuring servers can handle requests effectively.
• Email delivery: DNS resolves email addresses’ domain names, facilitating the proper routing of email messages across mail servers.
• Internet services and applications: DNS is vital for web browsing, gaming, VoIP, file sharing, and more, eliminating the need to remember and manually enter IP addresses for each service.

What are the different types of DNS servers and queries?

Depending on their roles and functions, DNS servers are categorized into different types and queries. Here’s what you should know. 

Types of DNS servers:

Recursive DNS servers:

• Responsible for handling DNS resolution requests from clients. 
• Interact with other DNS servers to resolve domain names on behalf of the requesting clients. 
• Recursive servers typically cache the DNS responses they receive to improve future resolution performance.

Authoritative DNS servers:

• Responsible for storing and providing the authoritative DNS records for specific domain names. 
• Hold the definitive information about the IP addresses associated with the domain names they are authoritative for. 
• When a recursive server receives a query for a specific domain, it seeks the answer from the authoritative server for that domain.

Root DNS servers:

• Represent the foundation of the DNS hierarchy.
• Responsible for providing initial guidance in the DNS resolution process. 
• Root servers direct recursive servers to the appropriate TLD servers based on the requested domain name’s extension (.com, .org, etc.).

Top-Level Domain (TLD) DNS servers:

• Responsible for the TLDs in the DNS hierarchy, such as .com, .net, .org, and country-specific TLDs like .uk or .fr. 
• Hold the information about the authoritative DNS servers responsible for individual domains within their TLD.

Secondary DNS servers:

• Act as backup servers, mirroring the DNS information from primary authoritative DNS servers. 
• Help improve redundancy and reliability, ensuring that DNS records are available even if the primary server experiences issues.

Types of DNS Queries:

Recursive query:

• Initiated by a client (e.g., user’s device or DNS resolver) when it requests a resolution for a domain name. 
• Traverses through the DNS hierarchy, starting from the root servers, until it obtains the final IP address associated with the domain name.

Iterative query:

• Performed by a DNS server when it seeks DNS information from another DNS server. 
• Server sends a query and expects a response with the best available answer or a referral to another DNS server that might have the desired information.

Forward query:

• DNS request made by a DNS resolver to a DNS server, asking for the IP address associated with a domain name.

Reverse query:

• Also known as a Pointer (PTR) query. 
• Used to obtain the domain name associated with a given IP address. 
• Involves querying the special “in-addr.arpa” domain that is used for reverse DNS lookups.

What’s the difference between an authoritative DNS server and a recursive DNS resolver?

The main differences between an authoritative DNS server and a recursive DNS resolver include their roles, query handling, caching behavior, and security features.

Here’s how they differ: 

Function

• An authoritative DNS server is responsible for providing authoritative information about a specific domain.
• A recursive DNS resolver is responsible for fetching and providing DNS information to clients.

Query handling

• An authoritative DNS server responds to queries with the requested DNS information if it has the authoritative data for the queried domain. 
• A recursive DNS resolver processes client queries by recursively contacting other DNS servers to fetch the requested information.

Caching: 

• An authoritative DNS server typically does not perform caching as it serves as the source of truth for a specific domain. 
• A recursive DNS resolver caches the DNS responses it receives to improve future query performance and reduce network traffic.

Hierarchy: 

• Authoritative DNS servers are organized in a hierarchical manner, with each server responsible for a specific domain or zone. 
• Recursive DNS resolvers traverse the DNS hierarchy to resolve queries by querying authoritative DNS servers and other DNS resolvers.

Interaction with clients: 

• Authoritative DNS servers primarily interact with other DNS servers, responding to queries from recursive resolvers or forwarding requests to other authoritative servers. 
• Recursive DNS resolvers interact directly with client devices, receiving queries and providing DNS resolution services.

Trust: 

• Clients typically trust recursive DNS resolvers to provide accurate and secure DNS information, as they are responsible for fetching data from authoritative sources. 
• Authoritative DNS servers, being the trusted source of information for a specific domain, are relied upon by recursive resolvers and other DNS servers for accurate and up-to-date data.

Security and privacy: 

• Recursive DNS resolvers can implement DNS over TLS (DoT) or DNS over HTTPS (DoH) to encrypt DNS queries and responses, enhancing privacy and protecting against eavesdropping or tampering. 
• Authoritative DNS servers typically do not handle direct client queries, so these encryption protocols are not applicable. 

What is DNS caching and how does it impact web performance?

DNS caching involves temporarily storing DNS records in the cache of resolvers or clients. This allows for faster resolution during future domain lookups by retrieving the information from the cache rather than querying the DNS infrastructure again. 

DNS caching impacts web performance in the following ways:

1. Faster response times: caching DNS responses reduces the time to resolve subsequent queries, improving response times for accessing websites and online services by quickly retrieving IP addresses from the local cache.
2. Reduced network traffic: DNS caching lowers network traffic by decreasing the need for multiple queries to be sent to DNS servers, resulting in a more efficient network, and alleviating the load on DNS infrastructure.
3. Improved scalability: DNS caching enhances DNS service scalability by reducing query loads on servers and infrastructure, enabling them to handle a larger number of requests without performance degradation during periods of high query volumes.
4. Mitigation of DNS server failures: DNS caching helps mitigate the impact of DNS server failures or connectivity issues by relying on cached responses to continue resolving queries for a specified duration, ensuring uninterrupted access to websites and services.
5. Impact on content delivery: DNS caching plays a role in Content Delivery Networks (CDNs) by efficiently directing users to the nearest server location, reducing latency, and improving content delivery.

What attacks is DNS prone to?

DNS is susceptible to several types of cyber attacks. Here are some common attacks that target DNS:

• DNS spoofing or DNS cache poisoning: attackers manipulate DNS caches to redirect legitimate domain resolutions, leading users to malicious websites and intercepting their communications.
• Distributed Denial of Service (DDoS) attacks: DNS servers are overwhelmed with massive volumes of requests from multiple sources, rendering them unavailable and disrupting services for legitimate users.
• DNS tunneling: attackers encode malicious data within DNS queries or responses to bypass network security measures, establishing covert communication channels for data exfiltration or malware control.
• DNS hijacking: unauthorized access to DNS registrar or hosting accounts allows attackers to modify DNS records, redirect domain traffic to their controlled server for phishing, steal data, or distribute malware.
• DNS amplification: misconfigured DNS servers are exploited to launch DDoS attacks by sending small queries with spoofed source IP addresses which triggers larger responses and amplifies the attack scale.
• Domain Name System Security Extensions (DNSSEC) attacks: attacks such as DNSSEC zone walking, key management attacks, or denial-of-existence attacks can exploit vulnerabilities in DNSSEC implementations, compromising the integrity and security of DNS data.
• Fast flux DNS: Fast flux DNS is a technique used by botnets to hide the location of malicious servers by rapidly changing their IP addresses through DNS updates. This makes it difficult to identify and mitigate the botnet’s command and control infrastructure.

How can you prevent cyber attacks on DNS?

Preventing cyber attacks on DNS involves implementing various security measures and best practices. Here are ten strategies to help mitigate the risk of DNS-related attacks:

Use secure DNS protocols

Implement secure DNS protocols such as DNS over HTTPS (DoH) or DNS over TLS (DoT) to encrypt DNS traffic between clients and DNS resolvers. This prevents attackers from eavesdropping on or manipulating DNS queries and responses.

Implement DNSSEC

Deploy DNSSEC to add an additional layer of security to DNS, which uses digital signatures to verify the authenticity and integrity of DNS records, protecting against DNS spoofing and cache poisoning attacks.

Regularly update DNS software and patches

Keep DNS server software up to date with the latest security patches and updates. This helps address known vulnerabilities and reduces the risk of exploitation by attackers.

Employ DNS firewalls

Implement DNS firewalls or DNS filtering solutions that can analyze and block malicious DNS queries or suspicious domain name requests. These tools can prevent access to known malicious domains and provide protection against malware, phishing, and other threats.

Enable Response Rate Limiting (RRL)

RRL is a technique that limits the number of responses a DNS server sends to prevent DNS amplification attacks and reduce the impact of Denial of Service (DoS) attacks targeting DNS infrastructure.

Implement DNS logging and monitoring

Enable DNS logging and implement robust monitoring solutions to detect and analyze traffic for any unusual or suspicious activities. This helps identify potential attacks or anomalous behavior, allowing for timely response and mitigation.

Apply strong access controls

Implement strict access controls and secure configurations for DNS servers, including restricting access to authorized personnel only. This reduces the risk of unauthorized changes or malicious activities targeting DNS infrastructure.

Conduct regular security audits and penetration testing

Perform regular security audits and penetration testing on DNS infrastructure to identify vulnerabilities and assess the effectiveness of existing security measures. This helps identify potential weaknesses and allows for proactive remediation.

Educate and train personnel

Provide education and training to IT staff and users about DNS security best practices, such as recognizing phishing attempts, avoiding suspicious links, and maintaining strong passwords. Human awareness and vigilance are critical in preventing social engineering attacks that can target DNS.

Establish redundancy and backup

Implement redundancy and backup measures for DNS infrastructure to ensure continuous availability and resilience. This includes setting up secondary DNS servers, employing geographically distributed servers, and maintaining regular backups of DNS configurations and data.

Final thoughts

DNS serves as the backbone of the internet, translating user-friendly domain names into machine-readable IP addresses. However, DNS is not immune to cyber attacks. On the contrary, bad actors can exploit vulnerabilities found in the DNS infrastructure and unlock a potentially devastating chain of reactions.

Hijacking, spoofing, and DDoS attacks are just a few of the sinister tactics hackers employ. By prioritizing DNS security, organizations can fortify their online presence, protect sensitive data, and ensure uninterrupted access to vital online services.

Organizations must know what DNS is and how this vector may be susceptible to cyber attacks. For more information about DNS and advice on how to reduce the likelihood of a security breach, reach out to a member of our team.