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: ma...@isc.org
