In the DNS hierarchy, each level, from the root to top-level domains (TLDs), second-level domains (SLDs), and subdomains, is managed by computers known as “nameservers”. Nameservers are specialised servers responsible for storing and maintaining information about the domain names within their level of the hierarchy.
Root nameserver
The root nameservers are the highest-level DNS servers in the DNS hierarchy, the do not store DNS records for a specific domain name. Instead they maintain information about the authoritative nameservers responsible for TLDs. Root nameservers are distributed around the world each set of root nameservers consists of multiple individual servers and they maintain the same information about the root zone. This redundancy ensures the high-availability of DNS. When a request is made, one of the nearest server will handle the request through the “anycast” routing method.
Authoritative nameserver
Authoritative nameservers are responsible for specific domains (zones) and are settled at various level of the DNS hierarchy. The authoritative nameservers are distributed for the high-availability and robustness of the DNS.
Top-Level Domain (TLD) nameservers
Below the root, each TLD, including ccTLC and gTLD has its own set of authoritative nameservers. For instance the .com gTLD has serval authoritative nameservers, each of the authoritative nameserver manages information about the authoritative nameservers of SLDs within that TLD.
These nameservers are also distributed and typically consists of multiple servers for redundancy.
Second-Level Domain (SLD) nameservers
At the domain level, authoritative nameservers for specific domains (i.e. organisation, personal specific domain) are often hosted on multiple servers. For exampleThese authoritative nameservers are responsible for providing DNS information for their respective domains.
Subdomain nameservers
If a SLD has a subdomain (i.e. sub.example.com), the domain owner can further distribute the authoritative nameservers for those domains.
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Computer_networksINFO1112IP_modelApplication_layerDomain_Name_System_DNSDNS_resolutionDNS_hierarchyNameserverTop_Level_Domain_TLDSecond_Level_Domain_SLDSubdomain