DNS Root Servers: Quickly Answer Records Stored or Cached

The Domain Name System (DNS) servers can quickly answer queries for records stored or cached within the root zone, and they can also indicate other requests to the appropriate Top Level Domain (TLD) server.

The Domain Name System (DNS) administration is structured in a hierarchy utilizing various managed areas or “zones,” with the root zone at the top of that hierarchy. Root servers are DNS nameservers that serve in the root zone. The TLD servers are the DNS server collection one step beneath root servers in the DNS hierarchy, and they are DNS queries.

DNS Hierarchy

Meanwhile, in an Uncached DNS query, whenever a user reaches a web address into their browser, this action triggers a DNS lookup, and all DNS lookups begin at the root zone. Once the lookup goes to the root zone, the lookup will then travel down the hierarchy of the DNS system, first hitting the TLDs servers. Next, the servers for specific domains (and possibly subdomains) until it finally hits the authoritative nameserver for the correct field, including the website’s numerical IP address being sought. This IP address is then conveyed to the client. Interestingly, notwithstanding the number of steps needed, this process can happen very suddenly.

Root servers are an indispensable part of the Internet’s infrastructure; web browsers and many other internet tools would not operate without them. Thirteen addition, different IP addresses serve the DNS root zone, and hundreds of redundant root servers exist around the globe to handle requests to the root zone.

13 DNS Root Server Addresses

A popular misconception is that there are barely 13 root servers in the world. There are many more in certainty, but only 13 IP addresses are used to query the various root server networks. Defects in the unique architecture of DNS expect there to be a maximum of 13 server addresses in the root zone. In the initial times of the Internet, there was only one server for every of the 13 IP addresses. Most of these were established in the US.

Authority Over DNS Root Servers

Ultimate authority over the root zone refers to the National Telecommunications and Information Administration (NTIA), a US Department of Commerce division. The NTIA proxies management of the root zone to the ICANN, Internet Corporation for Assigned Names and Numbers. ICANN operates servers for one of the 13 IP addresses in the root zone and delegates the other 12 IP addresses to various organizations, including NASA, the University of Maryland, and Verisign, which is the only organization that operates two of the root IP addresses. Cloudflare helps implement DNS Anycast services to one of the root servers known as the F-Root; Cloudflare provides additional F-Root instances under contract with ISC (the F-Root operator). 

Resolvers encounter DNS Root Servers.

After the DNS root zone is at the peak of the DNS hierarchy, recursive resolvers cannot be conducted in a DNS lookup. Because of this, each DNS resolver has a record of the 13 IP root server addresses developed into its software. Thus, the Recursor’s primary communication is with one of those 13 IP addresses whenever a DNS lookup is initiated.

DNS Root Server grows Unavailable

Thanks to the application of Anycast routing and ample redundancy, the root servers are very reliable. But on rare occasions, a root server will have to update its IP address. In this case, recursive resolvers can continue using the other 12 IP addresses in the root zone to perform DNS lookups until their software is updated with the correct addresses of all 13 servers. Since all the root servers can forward DNS requests to TLD servers, there is no disruption to the normal operations of the Internet when one root server is down.

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