Every domain is a subdomain of something else other than the root. access.api.bbc.com is a subdomain of api.bbc.com and a subdomain of bbc.com and a subdomain of com and a subdomain of . (the root). All subdomains are domains. All domains can have subdomains except those that are maximal size and maximal size - 1. The minimum label size is 2 (length + value) except for the root which takes 1 octet (length == 0). Subdomain is just a relationship to a parent domain. A domain may or may not correspond to a zone cut. All domains have a parent domain except the root. Mark
On 25 Feb 2025, at 12:58, Harry Hoffman via NANOG <nanog@nanog.org> wrote:
Hi Folks,
Feel free to tell me this isn't the proper place for my question but given that networking and DNS are hand in hand I thought it might be reasonable to ask here.
In working with several OSINT sources for domain processing it seems like the way domains and subdomains are processed essentially equates subdomains with FQDNs.
For example, several APIs (and even ChatGPT) classify the following: access.api.bbc.com account-api.api.bbc.com account-api.int.api.bbc.com account-api.stage.api.bbc.com account-api.test.api.bbc.com account-cdn.test.api.bbc.com
with subdomains as either: all subdomains as api.bbc.com or as subdomains of access.api, account-api.api, account-api.int.api, etc.
instead of classifying as: api.bbc.com int.api.bbc.com stage.api.bbc.com test.api.bbc.com
Has this become common practice? Is there a definitive way to determine subdomains? I seem to recall that "older" dns server software wouldn't allow this but it could be that my memory is faulty.
Thanks!
Cheers, Harry
-- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: marka@isc.org