Types of DNS Servers

What is DNS

The Domain Name System (DNS) is the phonebook of the Internet. People access information online through domain names such as google.com. Web browsers communicate through Internet Protocol (IP) addresses. DNS translates domain names into IP addresses so browsers can load Internet resources.

Each device connected to the Internet has a unique IP address that other machines use to find the device. DNS servers eliminate the need to remember IP addresses such as 192.168.1.1 (in IPv4), or newer, more complex alphanumeric IP addresses such as 2400:cb00:2048:1::c629:d7a2 (in IPv6).

The domain name system (DNS) links URLs to their IP addresses. With DNS, it's possible to type words instead of numbers into a browser, allowing people to search for websites and send email using familiar names. When you search for a domain name in a browser, it shows the domain name.

It sends a query to the Internet to match the address of a website with the corresponding IP address. Once located, it uses the IP to retrieve the website's content. Most impressively, this entire process takes just milliseconds. DNS is known by many names, including name server, domain name system server, and nameserver server.

Types of DNS Server

All DNS servers fall into one of four categories: Recursive resolvers, root nameservers, TLD nameservers, and authoritative nameservers. In a typical DNS lookup (when there is no caching in play), these four DNS servers work together to complete the job of returning an IP address for a specified domain to a client (the client is typically a stub resolver or a simple resolver built into an operating system).

What is a DNS Recursive Resolver?

A recursive resolver (also known as a DNS recursor) is the first stop in a DNS query.The recursive resolver acts as a middleman between the client and the DNS nameserver. After receiving a DNS query from a web client, the recursive resolver will either respond with cached data, or send a request to the root nameserver, followed by another request to the TLD nameserver, and then finally a request to the authoritative nameserver.After receiving a response from the authoritative nameserver containing the requested IP address, the recursive resolver then sends the response to the client.

During this process, the recursive resolver will cache information from authoritative name servers. When a client requests the IP address of a domain name recently requested by another client, the resolver can circumvent the process of communicating with the nameservers, and deliver the request record from its cache to the client.

What is a DNS Root Nameserver?

The 13 DNS root nameservers are known to each recursive resolver, and are the first stop in the recursive resolver's search for DNS records. The root server accepts the recursive resolver's query that includes a domain name, and the root nameserver directs the recursive resolver to a TLD nameserver based on that domain's extension (.com, .net, .org, etc.). The root nameservers are overseen by a nonprofit called the Internet Corporation for Assigned Names and Numbers (ICANN).

Note that while there are 13 root nameservers, this does not mean there are only 13 machines in the root nameserver system. There are 13 types of root nameservers, but there are multiple copies of each one around the world, using anycast routing to provide quicker responses.

What is a TLD nameserver?

TLD nameservers hold information for all domain names that share a common domain extension, such as .com, .net, or whatever comes after the dot at the end of a URL. For example, the .com TLD nameserver holds information for every website that ends in '.com'. If a user was searching for google.com, after receiving a response from the root nameserver, the recursive resolver would then send a query to a .com TLD nameserver, which would respond by pointing to the authoritative nameserver for that domain.

Management of TLD nameservers is handled by the Internet Assigned Numbers Authority (IANA), which is a branch of ICANN. IANA breaks TLD servers into two main groups:

1. Generic top-level domains: These are domains that are not country specific, some of the most well-known generic TLDs are .com, .org, .net, .edu, and .gov.

2. Country code top-level domains: These include any domain that is specific to a country or state. Examples include .uk, us, .ru, and .jp.

There is actually a third category for infrastructure domains, but it is almost never used. This category was created for the arpa domain, which was a transitional domain used in the creation of the modern DNS; its significance today is mostly historical.

What is Nameserver?

When a recursive resolver gets a response from a TLD nameserver, it will direct the response resolver to an authoritative nameserver. The authoritative nameserver is usually the final step for the resolver to get an IP address. The authoritative nameserver has information specific to the domain name it serves (such as google.com) and it may provide the recursive resolver with the IP address of that server found in the DNS record, or if the domain has a CNAME record (alias) it will provide the recursive resolver with another domain, the dot (.) on which the recursive resolver must do a whole new DNS lookup to get the record from the authoritative nameserver (often a record containing an IP address). Cloudflare DNS distributes authoritative nameservers, which come with Anycast routing to make them more reliable.

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