DNS

DNS (the Domain Name System) is the internet’s directory service, translating human-readable domain names like adminkit.net into the numeric IP addresses computers actually use to route traffic. A DNS lookup walks a hierarchy of servers — root, top-level-domain, and authoritative nameservers for the specific domain — to resolve a name to its records, which can include an A/AAAA record (the IP address), an MX record (mail server), a TXT record (often used for SPF/DMARC or domain verification), and more. Every authentication mechanism email relies on, and most of the web’s addressing, sits on top of DNS working correctly and resolving quickly. A query for a name that doesn’t exist anywhere in the hierarchy gets back NXDOMAIN rather than an empty answer. A domain name containing non-ASCII characters is converted to its ASCII Punycode form before DNS performs that translation, since DNS labels are ASCII-only. DNS’s concepts and facilities are specified in RFC 1034; the implementation and record formats, including the ones listed above, are specified in RFC 1035, and the current record types, opcodes and other DNS parameter values are maintained in IANA’s DNS Parameters registry.