Appendix A. Emerging Internet Technologies
Because VPNs ultimately use the Internet as their transport medium, they are subject to the advantages and disadvantages associated with using the Internet Protocol (IP). As you are probably aware, the mechanics of the Internet (the TCP/IP protocols) rely not exactly on the familiar names that we are used to seeing in URLs, such as www.ibm.com and ftp.uu.net, but rather on a lower level addressing scheme that uses IP addresses or “dotted quads.” An IP address, such as 220.127.116.11, specifies precisely one computer. The IP address is the lowest common denominator separating one machine from another.
A hot topic among networking professionals is that the current pool of IP addresses is drying up. Since the IP address is formed by putting 4 bytes together, with each byte having 256 combinations (28), there is a limited number of IP addresses available (232, or 4,294,967,296, to be exact). You may be thinking that four billion addresses is nothing to sneeze at, which is true, but the explosive growth of the Internet world-wide has caused a great strain on the system for deploying those addresses. One reason for this is that huge blocks have already been given out and the system for assigning new ones is antiquated and difficult to administer.
The current version of the IP protocol is Version 4, and Version 5 disappeared while still under discussion. IP Version 6 (IPv6 for short) is a project supported by networking companies, technology ...