namelookup

Name lookup, or name resolution, is the process by which a system translates a human-readable host name into a numeric network address, enabling connections across networks. It is central to Internet and local-network communication and may involve multiple sources, including the Domain Name System (DNS), the hosts file, and local caches. In software, name lookup can also resolve service names to ports.

The primary mechanism is DNS. A client resolver asks a configured recursive DNS resolver, which traverses the DNS hierarchy: root servers direct queries to top-level domain servers, which delegate to authoritative servers for the specific domain. The final address is returned, and cached locally to speed subsequent requests. DNS typically uses UDP port 53, with TCP used for larger responses or zone transfers.

Name resolution can also include reverse lookups, mapping an IP address back to a domain name via in-addr.arpa or ip6.arpa. Local overrides such as the hosts file (and, on some networks, mDNS) provide alternative means of resolution, especially for offline or private networks. If a lookup cannot be completed, the system may return NXDOMAIN or no data.

Security and privacy considerations include DNSSEC, which adds origin authenticity and data integrity to DNS data, though it does not by itself conceal queries. For privacy, users may rely on encryption-based transports such as DNS over HTTPS (DoH) or DNS over TLS (DoT). Misconfigurations, cache poisoning risks, or compromised resolvers can lead to incorrect mappings or interception.

Common tools for diagnosing name lookups include nslookup, dig, and host, as well as system utilities such as getaddrinfo. Latency is affected by TTL values, caching, and resolver performance. Troubleshooting typically involves checking resolver configuration, network reachability, and ensuring DNSSEC validation if enabled.