The field "Starting domain name" must contain a subdomain of the field "Ending domain name".

A domain name must contain at least two segments.

A domain name may not end with a period (.).

A domain name may only contain alphanumeric characters, dashes, and periods.

The last segment in a domain name may only contain letters.

Domain names may not contain adjacent periods.

Domain names may not start with a period (.).

Invalid domain name error.