. The Open System Interconnect (OSI) [1] model defines seven layers. The Internet model, however, only defines five. The Internet technologies range from the layer three (network layer) upwards. Robustness Principle The Postel's robustness principle, also known as Postel's law, has gotten its name from its inventor - Jon Postel. Jon Postel was one of the Internet pioneers who has had an enormous effect on the Internet and its design through his contribution in engineering and governance. The principle is quoted as 'Be liberal in what you accept, and conservative Deploying IPv6 in 3GPP Networks Application Layer 7 Presentation Layer 6 Application Session Layer 5 Transport Transport Layer 4 Network Layer 3 Link Layer Data Link Layer Layer 2 Physical Layer Physical Layer Layer 1 Internet Figure 1.1 Networking layers. in what you send. [2] This principle means that the sender should be very conservative and strictly cohere with the standard, whereas the receiver should be able to receive even input that does not strictly conform to the standard. This is a very important principle for interpretability, and when making future extensions and improvements to the technologies. Creative Anarchy The final principle, creative anarchy, is something that seems to be at odds with proper telecommunications networking. However, this means that anyone (from a single indi- vidual to large enterprises or operators) can create and distribute new services and applications. This principle can be perhaps seen more as a symptom of the other principles, but comprehending it is still important to understand the Internet and its technologies. Without the creative anarchy principle, the Googles, Facebooks, and the like of this world would never have seen the light of day! 1.3 The Internet Protocol The most important building block in the Internet is the Internet Protocol. IP is the networking protocol that ensures that packets travel from the source through the network and reach the right destination. Currently two versions of the Internet P