Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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?

share|improve this question
My advice is not to get bogged down in detail - even within businesses these definitions vary. If it helps, I rarely here the phrase extranet - most people either declare something as being public facing (Even if it's restricted by passwords) or internal. The DMZ is merely a networking concept with regards to firewalls and security - you can host a website in front of the DMZ, in the DMZ or behind the DMZ and it's still an external website if it can be accessed from the internet. – Dan Aug 21 '14 at 11:34
@Dan, I wouldn't get stuck with this if it was real life, see my comment to MDMarra's answer. Maybe I'll try to avoid mentioning extranets altogether... – Markus Yrjölä Aug 21 '14 at 12:29
up vote 13 down vote accepted

These are academic distinctions. In the real world, you will find some combination of all of these concepts going by different terms.

In some organizations, a DMZ has a separate ISP network connection and has no access to internal resources. In other organizations, there are domain-joined machines in the DMZ that can communicate to a restricted set of internal machines. Sometimes internal and DMZ have separate firewalls. Sometimes they have separate interfaces on the same firewall.

It is important to know why someone should use an extranet or DMZ, because those are the security concepts that matter. From there, you can make a choice about how to allow access to certain resources. What it is actually called doesn't matter. In some cases, it is splitting hairs.

share|improve this answer
Funny that you started your answer like that, given that I asked this question as a part of the research I'm doing for my master's thesis. So unfortunately, I have to get academic with this stuff. Oh well, I guess I'll just have to try to define the terms somehow and provide some reasoning for it. – Markus Yrjölä Aug 21 '14 at 12:23

I don't think I've recently heard of an extranet outside of textbooks and class rooms.

A DMZ is a common networking topology with a network segment that is segregated by firewalls from the internal network and untrusted external networks (aka the internet).

In contrast the Extranet, if it is actually included in the network design, implies somewhat that it is connected to VPN's or actual private networks instead of the whole of the greater internet.

Many companies have multiple DMZ networks and would consider a network with a VPN gateway/router or a private interconnect just another DMZ.

More often an extranet is/was not so much a network topology but more implied to be a service separate from the internal network that is provided for a restricted set of somewhat trusted, known and/or authenticated external users, companies and networks.

From a networking perspective your webserver should reside in the DMZ network. The fact that your website allows your resellers to log in, browse your catalog, view stock and order, would mean that your website would be called an extranet by marketing departments. Development cost would go from $$ to $$$$.

share|improve this answer
Thanks, this clarified a few things up and matches pretty well with how I understood it myself. I've recently heard people talking about extranets at work, though, so apparently it's not a dead term. – Markus Yrjölä Aug 21 '14 at 13:08

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.