This is, in fact, the most common type of VPN –

This is, in fact, the most common type of VPN – one in which there are geographically diverse subnetworks which belong to a common

administrative domain, interconnected by a shared infrastructure outside of their administrative control (such as the global Internet or a

single service provider backbone).  The principle motivation in establishing a VPN of this type is that perhaps the majority of

communications between devices within the VPN community may be sensitive in nature (again, a decision on the level of privacy required

rests solely on a risk analysis performed by the administrators of the VPN), yet the total value of the communications system does not

justify the investment in a fully private communications system which uses discrete transmission elements.

On a related note, the level of privacy a VPN may enjoy depends greatly on the technology used to construct the VPN.  For example, if

the communications between each VPN subnetwork (or between each VPN host) is securely encrypted as it transits the common

communications infrastructure, then it can said that the privacy aspect of the VPN is relatively high.

In fact, the granularity of a VPN implementation can be broken down further to a single end-to-end, one-to-one connectivity scenario.

Examples of these types of one-to-one VPN's are single dial-up users establishing a VPN connection to a secure application, such as an

online banking service, or a single user establishing a secure, encrypted session between a desktop and server application, such as a

purchasing transaction conducted on the World Wide Web.  This is type of one-to-one VPN is becoming more and more prevalent as

secure electronic commerce applications become more mature and further deployed in the Internet.

It is interesting to note that the concept of virtualization in networking has also been considered in regard to deploying both research and

production services on a common infrastructure.  The challenge in the research and education community is one where there is a need to

satisfy both network research and production requirements.  VPN's have also been considered as a method to segregate traffic in  a

network such that research and production traffic behave as "ships in the night," oblivious to one another's existence, to the  point that

major events (e.g.  major failures, instability) within one community of interest are completely transparent the other.  This concept is

further documented in MORPHnet [4].