I've been reading about intranets, extranets, DMZs and VPNs now, and I'd need some clarifications related to extranets and DMZs. I understand that they are different types of concepts - extranet allows limited access to some intranet resources, while DMZ is a subnet that sits between the internet and intranet and hosts the external-faced services. However, I'd like to know what is their distinction in practice in a usual setup? The Wikipedia article on extranets says that extranets are similar to DMZs because they are used for the same purpose (providing access to some services/resources without exposing the whole intranet). The article also states that an extranet is a part of a VPN, and this TechNet article also states that extranet access is often implemented similarly to remote intranet access, e.g. with a VPN. The TechNet article also says that commonly the extranet is hosted inside the DMZ. This Pearson article says "Although [the DMZ] is technically located within the intranet, [it] can serve as the extranet as well". This is slightly confusing.
Consider this scenario: A company has a B2C website hosted in the DMZ. The website can be accessed from anywhere, but requires user authentication. The underlying web app has its database inside the intranet and also interacts with some web services that are hosted inside the intranet (i.e. it accesses intranet resources). The way I see it, the website does effectively offer a restricted access to the intranet. But can it be considered an extranet? If we take the Wikipedia definition of an extranet literally - "An extranet is a computer network that allows controlled access from outside of an organization's intranet" - I think it can.
Let's say that the above can't be considered an extranet. What if we change the scenario slightly, and say it's a B2B website, where the access is e.g. limited to connections coming from a specific business partner (by using site-to-site VPN, for example). In this case it surely is an extranet, right? If this is the case, then the difference between extranet services and any other services hosted in the DMZ is simply access restrictions?