 word 'network' is very confusing. The IP networks come big and small. Some of them are connected to the Internet, and some of them are not. An example of the smallest possible IP network is two nodes directly connected to each other exchanging data. An example of such a small network may be just a single peripheral connected to a computer. As IP is a well standardized and supported networking protocol, sometimes Introduction even these simple connections are more favorable to do with IP rather than using an application specific protocol. The Internet is said to be a network of networks. This description actually fits smaller IP networks, as well. Usually a section of a network, which is under one administrative control, is called a network. This can range from a peripheral connected to a single computer under the 'administrative control' of the computer's user, through a small home network, to large corporate or operator networks with thousands of nodes. These administrative domains can either be isolated or interconnected to other networks under a different administrative control. A good example is a home network; this has different nodes such as network attached storage, game consoles, different computers, etc. These create a network and communicate to each other sharing music, pictures, and other information. This home network may then be interconnected to an operator network such as an Internet Service Provider (ISP). The ISP is then connected to other Internet Service Providers. All these different ISPs (and the small home networks, and bigger enterprise networks) create the Internet. IP itself does not have separate User-to-Network Interface (UNI) and Network-to- Network Interface (NNI) protocols, but IP handles the networking between the end-hosts, the network nodes, and the different networks in the same way. Hence, IP creates networks of networks. 1.3.2 Routing and Forwarding The hosts in an IP network communicate between each other by sending IP packets. The source host has to know the IP address of th