DNS Server Types: 3 Ways to Classify Servers + Queries

DNS Server Types: 3 Ways to Classify Servers and Intro to Query Types

DNS Server Types: 3 Ways to Classify Servers and Intro to Query Types blog image

DNS server types can be classified into three main categories based on functional differences, relational differences, and availability and accessibility differences.

In this article, we will dive into these classifications to provide a comprehensive understanding of the various DNS server types and how they operate within these frameworks.

 

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Takeaways
  • There are three main categories of DNS servers – functional, relational, and availability/accessibility
  • Using a secondary DNS server comes with several advantages such as redundancy, zone transfer, load balancing and more
  • There are 3 main DNS query types – recursive, iterative and non-recursive type

What Types of DNS Servers Are There?

There are several types of DNS (Domain Name System) servers that serve different purposes within the DNS infrastructure. They can be categorized in different ways based on their functions, relationships, and availability.

Functional Differences: DNS servers are categorized based on their primary roles and responsibilities within the DNS hierarchy. Here are the key types:

  • Recursive Resolvers
  • Root Name Servers
  • TLD Name Servers
  • Authoritative DNS Servers

Relational Differences: DNS servers are classified based on their relationships with other servers in the DNS system. They include:

  • Primary DNS Servers
  • Secondary DNS Servers

Availability and Accessibility Differences: While less common, DNS servers can also be classified by availability and accessibility:

  • Public DNS Servers
  • Private DNS Servers

Below, we’ll dive deeper into each DNS server classification.

Two Types of DNS Servers: Relational Classification

There are two key types of DNS servers in the relational classification. Below, we’ll talk about them in detail.

  1. Primary Server

DNS servers are responsible for translating domain names into numeric IP addresses. That way, you can easily visit different websites on the internet using a human-readable, memorable label instead of long numerical IP addresses.

A primary DNS server hosts the primary zone file of a website, which is a text database that contains authoritative information for a domain, including IP addresses and domain administrator identity. It also holds different resource records, listing domain names alongside their corresponding IP addresses.

Primary servers also make necessary changes to the domain’s DNS records, and once updated, they communicate these changes to secondary servers.

There are several types of DNS records that primary servers can modify:

  • A record: Leads a domain to an IPv4 address
  • AAAA record: Leads a domain to an IPv6 address
  • MX Record: Designates a mail server for a domain.
  • NS Record: Specifies authoritative DNS servers for a domain.

It’s worth noting that a server can be set to be primary for one DNS zone, and secondary for another zone. The configuration of a DNS server depends on the server administrator. Each zone is limited to one primary DNS server.

  1. Secondary Server

Secondary DNS servers hold read-only copies of the zone file from the primary DNS server. They can handle DNS queries for a domain but cannot modify the zone files.

Secondary servers receive updates from the primary server through a process called zone transfer. If multiple secondary servers are in use, one may be designated as a higher-tier secondary server capable of replicating zone file copies to the remaining pool of secondary servers.

There are several benefits of using a secondary server. Here are some of them.

  • Redundancy: They provide a backup in case the primary server fails, ensuring continued DNS resolution.
  • Load Balancing: Distributes DNS queries, reducing the load on the primary server and improving response times.
  • Geographical Distribution: Locating secondary servers in different geographical locations can result in faster DNS resolution for users in varying locales.
  • Zone Transfer: Allows for the distribution of DNS information across various servers, helping in maintaining consistency in DNS records.
  • Fault Tolerance: Enhances the DNS system’s ability to continue functioning even when one or more servers encounter issues.

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Four Types of DNS Servers: Functional Classification

DNS servers can also be classified based on their function. Below, we detailed four types of DNS servers.

  1. Recursive Resolvers

Recursive resolvers, sometimes referred to as caching servers, act as intermediaries between web clients and DNS nameservers. Upon receiving a DNS query, they either respond with cached data or initiate a sequence of requests to root, TLD, and authoritative nameservers to fetch the necessary information.

This process begins with a request to a root nameserver, followed by a request to a TLD (Top-Level Domain) nameserver based on the domain’s extension, and concludes with a request to an authoritative nameserver for the specific domain in question.

It’s worth noting the caching function, where data received from authoritative nameservers is stored temporarily to expedite responses to identical future queries.

Recursive Resolver Example

A well-known example of a recursive resolver is Cloudflare’s 1.1.1.1 DNS service.

When a user makes a DNS query, the 1.1.1.1 resolver starts by checking its cache for the domain information. If the information isn’t cached, it proceeds to interact with root, TLD, and authoritative DNS servers to retrieve the necessary DNS records.

It then returns the domain’s correct IP address to the user, while caching the obtained data for future similar requests, thus enhancing the efficiency of subsequent DNS lookups

  1. Root Name Servers

Root name servers serve as the initial contact point for recursive resolvers. When a recursive resolver issues a query for a domain, the root name server responds by redirecting it to the appropriate TLD nameserver based on the domain’s extension (e.g., .com, .net, .org).

The global DNS system comprises 13 root name servers, managed and overseen by the Internet Corporation for Assigned Names and Numbers (ICANN). Each root name server type has multiple instances worldwide, utilizing Anycast routing to optimize response times.

Despite there being only 13 types, the total number of root name servers exceeds 600, significantly bolstering the DNS system’s resilience and efficiency​.

Root Name Server Example

A good example of a root name server is the “A” root server operated by Verisign. It’s one of the 13 root name servers in the global DNS infrastructure.

The “A” root server plays a critical role in directing recursive resolvers to the appropriate TLD name servers based on the queried domain’s extension. Verisign, being a reputable entity in the domain name industry, ensures that the “A” root server operates with high reliability and robustness to maintain the overall stability and functionality of the DNS system.

  1. TLD Name Servers

TLD (Top-Level Domain) name servers maintain records for all domains sharing a common extension like .com, .net, etc. For instance, a .com TLD nameserver houses information for every domain ending with .com.

Managed by the Internet Assigned Numbers Authority (IANA), a subsidiary of ICANN, TLD nameservers are crucial for guiding recursive resolvers to the authoritative nameservers of specific domains.

They are categorized into generic top-level domains (gTLDs like .com, .org) and country code top-level domains (domain extensions like .uk, .us). TLD nameservers are an integral part of the DNS lookup process, bridging the gap between root name servers and authoritative name servers​.

TLD Name Server Example

An example of a TLD (Top-Level Domain) name server is a set of name servers responsible for managing all domains ending in “.com”. These servers store information necessary to direct requests to the authoritative DNS servers for each “.com” domain.

When a recursive resolver queries for a domain like “example.com”, it will be directed to the “.com” TLD name server, which in turn points it to the authoritative name server where the actual DNS records for “example.com” are stored.

This hierarchy streamlines the DNS lookup process, ensuring that domain name queries are resolved efficiently and accurately.

  1. Authoritative DNS Servers

Authoritative DNS servers are the final destination in the DNS lookup query, holding the actual DNS records for domains. They provide the necessary information requested, whether it’s an IP address (found in the DNS A record) or an alias domain (found in the CNAME record).

When the recursive resolver receives direction from a TLD nameserver, it queries the authoritative nameserver to obtain the required data.

Companies like Cloudflare offer robust authoritative DNS services, enhancing reliability and response times with Anycast routing.

By distributing authoritative nameservers strategically worldwide, they ensure rapid DNS resolution and superior uptime, which is indispensable for maintaining a seamless online presence​.

Authoritative DNS Server Example

For example, Cloudflare provides a service providing an authoritative DNS server. Cloudflare’s DNS service houses the actual DNS records for numerous domains, providing accurate information required for resolving domain names to IP addresses.

When queried by a recursive resolver, Cloudflare’s authoritative DNS servers provide the necessary data such as A records (IPv4 addresses) or AAAA records (IPv6 addresses) enabling the correct routing of internet traffic to the respective servers.

Through Anycast routing, Cloudflare ensures fast DNS resolution and a high level of reliability, making it a popular choice for domain owners seeking robust DNS services.

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Availability and Accessibility Classification of DNS Servers

DNS server classification into public and private DNS servers is based on availability and accessibility.

Public DNS Servers

Public DNS servers are accessible to anyone on the Internet. They are often provided by third parties like Google or Cloudflare, aiming to offer faster and more reliable DNS resolution compared to default servers provided by ISPs.

Note

An example of public DNS is Google’s 8.8.8.8 DNS service which offers speedy DNS lookups and added security features.

Public DNS servers often provide additional features like security filtering to block malicious websites, phishing protection, and parental controls to filter out inappropriate content.

They may also offer improved performance and reliability through global server networks and advanced routing technologies, ensuring quick responses to DNS queries.

Private DNS Servers

Private DNS servers enable a controlled environment, where access to specific domain names is restricted only to authorized individuals. This ensures more security and privacy. They’re important because they help manage internal network resources, enforce network policies, and handle internal traffic efficiently.

Private DNS allows organizations to maintain a structured domain naming system, easing the administration and management of network resources. Private DNS servers also help in reducing the exposure to external threats, providing a safer and more organized infrastructure.

What Are the 3 DNS Query Types?

A DNS query is a request made by a client to a DNS server to resolve a domain name to its corresponding IP address or other associated records.

This process is fundamental for navigating the internet as it enables the translation of human-readable domain names (e.g., example.com) into machine-understandable IP addresses (e.g., 192.0.2.123). Below, we listed the 3 DNS query types.

DNS Query TypeDescription
Recursive DNS Query
  • DNS client provides a hostname
  • DNS Resolver initiates a process starting from the DNS Root Server, moving down the hierarchy to reach the Authoritative Name Server for the requested hostname
  • Resolver returns information or an error message to the client
Iterative DNS Query
  • DNS client provides a hostname
  • DNS Resolver returns the best answer based on its current knowledge
  • If relevant DNS records are in the cache, it returns them; otherwise, it refers the client to the Root Server or closer Authoritative Name Server
  • The client repeats the query directly to the referred DNS server until it finds the required information
Non-Recursive DNS Query
  • DNS Resolver already knows the answer, either from the local cache or by querying an authoritative DNS Name Server
  • The resolver immediately returns the DNS record to the client, avoiding additional rounds of queries.
  • This process is faster than recursive or iterative queries.

Final Word

DNS servers are an important part of the Internet infrastructure. They translate human-readable domain names into machine-readable, numerical IP addresses. They come in various types, each serving a specific role in the DNS query process. After reading this article, you should have a good understanding of DNS server types and DNS queries.

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Next Steps: What Now?

Learn More About DNS

Frequently Asked Questions

What are the types of DNS servers on Linux?

There are various types of DNS servers available for Linux, including:

  • Primary (Master) DNS Server: Holds original read-write copies of all zone records.
  • Secondary (Slave) DNS Server: Holds a read-only copy of the zone data, transferred from a master server.
  • Caching DNS Server: Stores temporary data of recent queries to reduce the response time for subsequent queries.
  • Forwarding DNS Server: Forwarding DNS queries to other DNS servers for resolution, reducing the load on local servers.
What is the most common DNS type?

The most common type of DNS server is the Caching DNS server as it significantly improves the speed of domain name resolutions by caching the results of previous queries for a specified amount of time.

How many main DNS servers are there?

There are 13 root DNS servers globally, labeled from A to M. These servers are operated by various organizations and are the backbone of the internet’s DNS infrastructure, directing queries to the appropriate top-level domain (TLD) servers.

How do I list all DNS servers?

To list all DNS servers, you can use various tools or commands depending on the system:

  • On Linux, use the cat /etc/resolv.conf command to list the DNS servers your system is configured to use
  • On Windows, use the command ipconfig /all and look for the entries listed under “DNS Servers”
  • Online tools like nslookup and dig can also provide information on DNS servers when queried for a specific domain
Sonja Vitas
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Sonja Vitas
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