DNS Root Sever
A DNS (Domain Name System) Root Server, or root name server, is at the very highest level of the DNS hierarchy and essentially manages domain names for the entire Internet.
What is a DNS root server?
Root DNS servers are the servers that literally run DNS for the entire Internet. If we look at the picture above, we see that the root server is actually even above the Top-Level Domain (TLD) servers. These root servers contain the root zone, which is essentially a list of all the Top-Level domains such as generic TLDs like .com and .net or country code TLDs (ccTLDs) like .is or .us.
The root zone is managed by IANA (Internet Assigned Numbers Authority) which is a part of ICANN (Internet Corporation for Assigned Names and Numbers). Root servers serve out this root zone.
As shown in the picture, DNS is hierarchical. IANA manages the root zone as well as the various non-sponsored Top-Level Domains. From there, individuals, groups, or companies may lease the use of domain names from a domain name registrar. These domain names are registered with authoritative servers within the hierarchy. If a domain name has not been cached by the client’s DNS server, that DNS server will go all the way to the root server to find the IP address assigned to a particular domain name within a URL.
How many DNS Root Server are there?
There are hundreds of root servers at various locations all over the globe. However, many times, people will believe there are only 13. This was a limitation of IPv4 addresses originally, and we only had one server for each IPv4 address represented in the table below. However, we now have clusters set up to ensure uptime and performance of the Internet, specifically DNS queries. Each of the hosts/IP addresses below actually have a server cluster behind it.
Originally these root servers were all in the US, but they have since been distributed around the globe. The clusters are highly available through the use of load balancing routers. For more information on root servers and where they are located you can go to root-servers.org.
List of Route Servers
Root Server Operator
University of Southern California (ISI)
University of Maryland
Internet Systems Consortium, Inc.
US Department of Defense (NIC)
US Army (Research Lab)
How do root servers work?
Root servers contain the root zone, as discussed above. WIthin this root zone are the records which help answer the client queries. You can actually see a full list of these records, kept by IANA here.
Without the root DNS servers, the Internet would no longer function. The diagram below shows that every time a client makes a query, unless that information has already been cached, it will start with the root servers. Simply put, every time you enter a URL in your browser, a root server will be integral to you getting to your destination.
How Root Servers Work
- The client asks the DNS server that it’s configured to go to for help getting to a particular destination.
- If the recursive DNS server doesn’t have that information cached it will go to the root server to see which TLD to go to.
- The recursive DNS server then checks with the appropriate TLD, which directs it to the authoritative name server.
- The authoritative name server will have the correct IP associated with the domain name and will pass that along to the recursive DNS server.
- The recursive DNS server will cache that information for a certain period of time, according to the configured TTL (Time-to-Live).
- The client will now have the information it needs to contact the destination domain name via the IP address.