The truth about in-addr.arpa

[Kevin Darcy]

Karma Crayona wrote:

> This might seem like a silly topic, but could someone please tell me if
> the following statements are true:
>
> 1) "arpa" is considered a TLD.
>
> 2) "in-addr" is considered an SLD.

No, "in-addr.arpa" is a SLD. "in-addr" is just a label that could appear
anywhere in a domain name.

> Also, since I can't find anything that says so outright, could you also
> answer these questions:
>
> 3) Where is it documented?

Where is the existence of "in-addr.arpa" -- and therefore by inference
"arpa" -- documented, you mean? In RFC 1035, for one. In the root servers,
for another. Or do you mean "where is the designation of 'arpa' and
'in-addr.arpa' as TLD and SLD, respectively, documented?". This derives
directly from the definitions of those terms: a TLD has only a single
label, not including the "root" label, and a SLD has 2.

> 4) Besides arpa, the ccTLDs, and gTLDs, are there others?

The "g" in "gTLD" stands for "generic", so it's pretty much a catch-all.
I don't know that any gTLD's have been added to the list since RFC 1591
was published, so the list of gTLD's there should encompass every
TLD that's not a ccTLD or the "special" arpa TLD.


- Kevin