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Domain Name Length Limits
- Authors
- Name
- hwahyeon
According to the DNS standard (RFC 1035), domain names have strict length rules:
| Part | Limit | Notes |
|---|---|---|
| Entire domain name | Up to 253 chars | Includes dots (.). Theoretical maximum is 255 bytes, but only 253 characters can be used safely. |
| Each label | Up to 63 chars | A label is each part separated by dots, e.g., www, example, com. |
Why 253 and not 255?
- RFC 1035 defines the maximum domain name length as 255 bytes.
- However, this includes:
- 1 byte for the length field of each label
- 1 byte for the null terminator at the end
- This leaves 253 characters for the actual domain name.
Implication
- In theory, the number of subdomains is almost unlimited.
- The practical limit comes from the total domain length (253 chars).
- Example:
a.b.c.d.e.f...example.comis valid as long as no label exceeds 63 chars and the whole stays under 253 chars.