DNS propagation and record resolution

Overview

DNS, the Domain Name System, maps a human-friendly domain such as example.com to the IP address a server actually listens on. It is the first thing that must happen before a browser can fetch a single byte, so almost every cannot load, site not found, and still showing old site mystery starts here.

Why lookups happen in order

1. The browser asks the resolver (your ISP or a public one) for the IP of example.com.
2. The resolver walks from the root servers through the TLD servers to the authoritative nameservers that your domain registrar or DNS host configures.
3. The authoritative nameserver returns the records, and the resolver caches them for the TTL (time to live) in seconds.
4. The browser gets the final IP and connects.

This is why a DNS change is not instant. Every cache between your editor and the browser's memory can hold the old value until its TTL expires.

Record types you will meet

• A: maps a name to an IPv4 address.
• AAAA: maps a name to an IPv6 address.
• CNAME: maps a name to another name, which the resolver then follows. Often used for www pointing at the apex, or CDN hosts.
• TXT: free-form text for verification (Google Search Console, email SPF/DKIM proofs) and policy records.
• MX: names the mail servers for a domain. This is separate from website DNS, which is why a site can work while email is broken.
• NS: declares which nameservers are authoritative for a zone.
• CAA: restricts which certificate authorities may issue certificates for the domain.

What propagation actually means

"Propagation" is the time taken for cached answers at every resolver to expire naturally. Clearing your local DNS cache only affects your machine. The wider caches follow their TTLs. If you set a short TTL before a planned change, old answers expire sooner and the change is live everywhere sooner. Lower the TTL before a move, then raise it again once stable.

Troubleshooting a DNS that is not resolving

1. Resolve with a public DNS server: nslookup example.com 8.8.8.8 or nslookup example.com 1.1.1.1 bypasses your local cache.
2. Check the authoritative source directly: nslookup -type=NS example.com finds the nameservers, then query them directly with nslookup example.com <nameserver>.
3. Compare several public resolvers. If Google shows the new IP but your ISP still shows the old one, you are in propagation, not misconfiguration.
4. Check the registrar. A domain whose nameservers were just changed at the registrar can take longer and affects NS lookups.
5. Remember that a working site on your phone does not mean DNS is done globally. Resolvers cache independently.