maximum size of a domain

[Steven Sakata]

I tried to register a long domain name with Network Solutions and was told
that there is a 26-character limit (including the four characters in .com).
I asked if this was a Network Solutions limitation or if this is a limitation
specified in an RFC.  I did not get a response.  Does anyone know what the
maximum character-length of a domain is and what RFC contains this information.

Thanks, Steven.