DNS

DNS (Domain Name System) is the distributed, hierarchical naming system that translates human-readable domain names — like example.com — into the IP addresses computers actually connect to. Often called the internet's phone book, it is critical infrastructure in the most literal sense: when DNS fails, websites and email become unreachable even though the servers behind them are perfectly healthy.

How DNS resolution works

When you type an address into a browser, a resolver (your ISP's or a public one such as 1.1.1.1 or 8.8.8.8) performs a recursive lookup:

1. it asks a root server which servers handle the .com zone,
2. the TLD server replies with the domain's authoritative name servers (its NS records),
3. an authoritative server returns the requested record — for example an A record containing the IPv4 address,
4. the answer goes back to the browser and is cached by the resolver for the duration set in the record's TTL.

Thanks to caching, the vast majority of lookups never leave the resolver and complete in milliseconds — which is also why zone changes propagate gradually rather than instantly.

Essential record types

• A / AAAA — IPv4 / IPv6 address of a host,
• CNAME — an alias pointing at another name,
• MX — mail servers accepting email for the domain (see MX record),
• TXT — free-form text used for SPF, DKIM, DMARC and ownership verification,
• NS and SOA — zone delegation and zone parameters.

DNS in practice

You touch DNS at every infrastructure change: pointing a domain at a hosting account, moving a site to a new server (updating A records), configuring email (MX plus authentication records), or fronting a site with a CDN. Records are edited in the control panel of your DNS provider or domain registrar. Operational best practices include lowering TTLs ahead of planned changes, running at least two name servers in separate locations for redundancy, and verifying records after any migration with dig or nslookup. For tamper-proof responses, zones can additionally be signed with DNSSEC.