A domain name is a path through a tree, written from the most specific part to the least specific.
www . example . co . in . │ │ │ │ └ the root (usually not written) │ │ │ └ top-level domain (TLD) │ │ └ second level, run by the .in registry │ └ the name the registrant holds └ a name the registrant creates in their own zone
Labels and length
- Each part between dots is a label: 1 to 63 characters.
- The whole name: at most 253 characters in text form (255 bytes on the wire).
- Host names use letters, digits and hyphens, and a label does not start or end with a hyphen.
- Case does not matter:
Example.COMandexample.comare the same name. - A name that ends with a dot (
example.com.) is fully qualified: it names the path all the way to the root.
Who is who
- Registry
- Runs a top-level domain: keeps the list of names and the TLD zone, and publishes the DS records. For
.inthis is the .IN Registry run by NIXI. - Registrar
- Sells names to the public and sends changes to the registry: nameservers, contacts, DS records.
- Registrant
- You: the person or company that holds the name, for a period you pay for.
- DNS host
- Runs the authoritative nameservers for your zone. It can be your registrar or another company.
Registration data can be looked up with RDAP, which is replacing the older WHOIS.
How a name is resolved
- Your device asks a recursive resolver (your ISP's, or 1.1.1.1, 8.8.8.8).
- The resolver asks a root server: "who runs
.in?" It gets the.innameservers. - It asks the
.inservers: "who runsexample.co.in?" It gets that zone's nameservers. - It asks those authoritative servers for
www.example.co.inand gets the address. - It keeps each answer for its TTL, so the next lookup can skip most steps.
With DNSSEC the resolver also checks a signature at every step, from the root key down. That is the chain of trust.
Names in other scripts
Internationalised domain names (IDNs) let you use scripts such as Devanagari, Telugu or Cyrillic. In the DNS they are stored as ASCII with the xn-- prefix (Punycode): भारत is xn--h2brj9c. Browsers show the native form. Our checker accepts both forms.
Zones and subdomains
When you hold example.com you can create any names under it (www, mail, api) without asking anyone. You can also delegate a subdomain to other nameservers with NS records, the same way the parent delegated to you. With DNSSEC, a signed delegation needs a DS record in your zone too.