On 23/03/18 01:17, Greg Wooledge wrote:
> On Thu, Mar 22, 2018 at 12:04:07AM -0000, Dan Purgert wrote:
>> Richard Hector wrote:
>>> I often see this alluded to, but struggle to find evidence - why
>>> shouldn't there be a postmaster@com, for example? Or perhaps cic@mil?
>>
>> It is my understanding that the TLDs are not themselves valid domains.
>> That is, a valid domain is by definition "domain.tld".
>>
>> I could be entirely wrong though.
>
>>From <https://en.wikipedia.org/wiki/Fully_qualified_domain_name>:
>
> A fully qualified domain name (FQDN), sometimes also referred to as
> an absolute domain name,[1] is a domain name that specifies its exact
> location in the tree hierarchy of the Domain Name System (DNS). It
> specifies all domain levels, including at least a second-level domain
> and a top-level domain.[2]
>
> Footnote [2]:
>
> April N. Marine; Joyce K. Reynolds; Gary Scott Malkin (March 1994).
> "Questions About the Domain Name System". Answers to Commonly asked
> "New Internet User" Questions. IETF. sec. 5. doi:10.17487/RFC1594. RFC
> 1594. Retrieved 29 April 2013. "If you think of the DNS as a
> tree-structure with each node having its own label, a fully qualified
> domain name for a specific node would be its label followed by the
> labels of all the other nodes between it and the root of the tree."
>
> RFC 1594 <https://tools.ietf.org/html/rfc1594>:
>
> A Fully Qualified Domain Name (FQDN) is a domain name that includes all
> higher level domains relevant to the entity named. If you think of the
> DNS as a tree-structure with each node having its own label, a Fully
> Qualified Domain Name for a specific node would be its label followed by
> the labels of all the other nodes between it and the root of the tree.
> For example, for a host, a FQDN would include the string that identifies
> the particular host, plus all domains of which the host is a part up
> to and including the top-level domain (the root domain is always null).
>
>
> Now, that's from 1994, and it's an "Informational" RFC ("does not specify
> an Internet standard of any kind"), but that's probably as authoritative
> as you'll get.
>
Thanks - Having read that paragraph of the RFC, it doesn't seem to
require any particular number of levels, only that all that exist are
present.
Richard
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