D-Link DFL-1600 User Manual page 214

194
computers began talking to each other. In the beginning, communication
was limited to local area communication links, but in time, people were
finding reasons to have their computers exchange information across greater
distances.
Fixed connections are usually very reliable as far as uptime and available
bandwidth is concerned. They are also fairly secure, as long as no one
attacks the telephony infrastructure or digs your optical fibres out of the
ground and attach their own equipment to it. Fixed long-distance
connections, provided that suitable security measures are taken, may be
considered "Private Networks".
However, fixed channels of communication are just that: fixed. If you hire a
fixed connection between company A and B, you only allow communication
between companies A and B. If several organizations would want to
communicate with each other in all directions, separate fixed connections
between all organizations would be needed. Such situations quickly escalate
beyond all manageability and cost efficiency:
- Two organizations only require 1 connection.
- Three organizations require 3 connections.
- Five organizations require 10 connections.
- Seven organizations require 21 connections.
- Ten organizations require 45 connections.
- 100 organizations require 4950 connections.
One could argue that maybe some communication could be done by the
way of intermediates. If I wish to talk to company B, maybe I can send my
data to company C that has a link to company B? That way I don't have
to have a link to company B of my own?
In some cases, and in a small scale, this may work. On the other hand, it
may not work at all even if it is on a manageable scale. Consider a company
that sells a product to ten customers who all compete with each other.
- Would any one of them accept that their orders and delivery
confirmations travel through the hands of one of their competitors?
- Hardly.
D-Link Firewalls User's Guide
Chapter 20. VPN Basics