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What is DNS?

DNS (Domain Name System) is a core service of the Internet. As a distributed database that can map domain names and IP addresses to each other, it can make it easier for people to access the Internet without having to remember the IP string that can be directly read by machines. DNS resolver is a server that points domain names to website space IP, allowing people to easily access websites through registered domain names. DNS consists of a resolver and a domain name server. The domain name server stores the domain names and corresponding IP addresses of all hosts in the network, and has the function of converting domain names into IP addresses. A domain name must correspond to an IP address. An IP address can correspond to multiple domain names at the same time, but an IP address does not necessarily have a domain name. The DNS protocol runs over the UDP protocol and uses port number 53. In the RFC document, RFC 2181 specifies DNS, RFC 2136 describes dynamic updates of DNS, and RFC 2308 describes reverse caching of DNS queries. Through DNS, you can find the URL you need to visit and send the information to your computer. There are two ways to query DNS: recursive query and iterative query. In a recursive query, if A requests B, then B, as the recipient of the request, must give A the answer he wants. In an iterative query, if recipient B does not have the exact content that requester A needs, recipient B will tell requester A how to obtain the content, but will not issue the request itself. When a user opens a Web browser, enters www.abc.com in the address bar, and presses the enter key to access, the computer will first access the host file local to the system. If the host file on the computer stores the IP address corresponding to domain name resolution, then the browser will directly access the website through the IP address. If the address corresponding to this domain name is not stored in the host file, the computer will first request the specified DNS server to query the ip address for this domain name resolution. If the DNS server caches this address, it will directly return the address to the computer. In general, DNS converts human-readable names (such as www.abc.com) into IP addresses (such as 192.0.0.1) that can be understood by computers, allowing users to access resources on the Internet through domain names rather than complex IP addresses.