On Wednesday, October 20, 2004, 1:06:58 PM, Steven Champeon wrote:
'subdomain.thatdomain.com' is a /hostname/. It's not a subdomain unless there are hosts /in/ that subdomain, a la
mail.subd.foo.com <-> - top level domain <-> - second level domain (or subdomain b/c auth delegated for hosts) <-----> - domain <--> <----------> \ -- subdomain (b/c auth delegated for hosts in the zone) -- host
Of course, I may be talking through my hat. But that's my reading of RFC 882. (e.g., a domain is defined by the subdomains it defines, usually in terms of the DNS zones that exist for that sub/domain).
subwebs = thatdomain.com/subweb
Why not just call them URL paths? We used to refer to these as "subsites" back in the day, but technically they're just URL paths in this context as there's no sense of their being components with multiple pages under them or anything.
An entire URI can be thought of as a path in that it describes a location through the Internet, services and server(s). The right hand side stuff with slashes can also be thought of as a path within a given web site.
A subdomain is something that's delegated to another zone. A zone is "an autonomously administered piece of the namespace" like an Autonomous System Number (ASN) is an autonomously administered network within the BGP routing space. Both can have distinctly different administration policies within their space.
A host is a name within the same zone. It can be thought of as a leaf or destination in the DNS hierarchy. A subdomain can be thought of as a node or branch or folder containing other subdomains or hosts. In a filesystem analogy, domains and subdomains are like directories or folders and hosts are like files.
So:
foo.bar.baz.com
can be be either a host in a subdomain, or a subdomain of a subdomain, depending on the zone delegations. It's impossible to tell which is the case externally if only looking at the fully qualified domain name (all four names above), as the "foo" could define either a host or a subdomain. And a subdomain can respond as a web site the same as a host-terminated name can. Some careful poking and prodding of the zone data can reveal the underlying structure, but that's way more than the average user can do. Usually only hostmasters and folks who administer DNS use the terms correctly or can reverse engineer someone else's domains, so it's probably not too useful to try to define subdomains versus hosts for the general public.
Jeff C. -- "If it appears in hams, then don't list it."