DNS is made up of numerous DNS servers that exist worldwide. No single DNS server holds all domain information; instead, a system called "delegation" is used to divide the management of domains. This allows the information required for name resolution to be managed in a decentralized manner. A domain that is managed in this way is called a "zone," and the DNS server managing a specific zone is referred to as the "DNS content server" or "authoritative DNS server" for that zone. On the other hand, a server that receives queries from users, makes requests to other DNS servers, and returns the results to users is called a "DNS caching server."
DNS servers are indispensable for operating the modern internet, but DNS servers with vulnerabilities can become targets for malicious attacks. Examples of such attacks include "delegation/transfer notification injection attacks" and "DNS flooding attacks." To protect against these kinds of attacks, the use of DNS proxies is effective. F5 provides the "F5 BIG-IP," which is equipped with DNS proxy functionalities.