SECURITY

Security
An extranet requires security and privacy. These can include firewalls, server management, the issuance and use of digital certificates or similar means of user authentication, encryption of messages, and the use of virtual private networks (VPNs) that tunnel through the public network.
Many technical specifications describe methods of implementing extranets, but often never explicitly define an extranet. RFC 3547 presents requirements for remote access to extranets. RFC 2709 discusses extranet implementation using IPSec and advanced network address translation (NAT).
Industry uses
During the late 1990s and early 2000s, several industries started to use the term "extranet" to describe central repositories of shared data made accessible via the web only to authorized members of particular work groups.
For example, in the construction industry, project teams could login to and access a 'project extranet' to share drawings and documents, make comments, issue requests for information, etc. In 2003 in the United Kingdom, several of the leading vendors formed the Network of Construction Collaboration Technology Providers, or NCCTP, to promote the technologies and to establish data exchange standards between the different systems. The same type of construction-focused technologies have also been developed in the United States, Australia, Scandinavia, Germany and Belgium, among others. Some applications are offered on a Software as a Service (SaaS) basis by vendors functioning as Application service providers (ASPs).
Specially secured extranets are used to provide virtual data room services to companies in several sectors (including law and accountancy).
There are a variety of commercial extranet applications, some of which are for pure file management, and others which include broader collaboration and project management tools. Also exist a variety of Open Source extranet applications and modules, which can be integrated into other online collaborative applications such as Content Management Systems.
Disadvantages
Extranets can be expensive to implement and maintain within an organization (e.g.: hardware, software, employee training costs) — if hosted internally instead of via an ASP.
Security of extranets can be a big concern when dealing with valuable information. System access needs to be carefully controlled to avoid sensitive information falling into the wrong hands.
Extranets can reduce personal contact (face-to-face meetings) with customers and business partners. This could cause a lack of connections made between people and a company, which hurts the business when it comes to loyalty of its business partners and customers.