A recursive DNS server is a domain name system server that takes website name or URL (uniform resource locator) requests from users and checks the records attained from authoritative DNS servers for the associated IP address.
Recursive DNS servers are required to support the authoritative DNS servers, which would not otherwise be able to handle the workload created by the huge number of user requests. Recursive DNS servers further distribute this load to make website name requests supportable.
When a user types in www.whatis.techtarget.com, for example, this address itself does not contain the direction to find the site on the internet. It is only through DNS servers that the IP address is located and used to reach the site (unless the request has been made before from that computer and the response IP address has been cached locally).
Recursive servers are the first ones contacted as the result of a request. Should the contacted server have a cached response for the IP address from an authoritative server with a valid time to live (TTL), it is delivered. If the recursive server doesn’t have the IP address, then it begins its check through the hierarchy of authoritative DNS servers. Authoritative DNS servers in turn have their records supplied by the internet registrars where website owners set up their site names.
DNS servers are a weak point in the internet, as was demonstrated in late 2016 when a wide-scale botnet attack took down access to many major sites.