Domain Name System (DNS)
The internet's address book — translates human-readable domain names (nessimworks.com) into IP addresses servers can route to.
In long form.
DNS is a hierarchical system: root servers point to TLD servers (.com, .org), which point to authoritative nameservers for each domain, which return the actual records. Common record types: A (IPv4 address), AAAA (IPv6), CNAME (alias to another domain), MX (mail server), TXT (verification, SPF/DKIM, etc.), NS (delegate to other nameservers). Changes propagate based on TTL — common values are 300s (5 min) for active changes, up to 86400s (24 hr) for stable records.
When a site move goes wrong, the issue is usually DNS — a record pointing to the wrong server, a TTL that hasn't expired, or a missing CAA record blocking SSL issuance. We always document existing DNS before any migration and lower TTLs 24-48 hours before a planned change.
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