 of the available interfaces. 1.4 Internet Protocol Addresses Regardless of whether a network is big or small, the IP addresses have to be unique within the network. As described above, the IP packet's destination address is used to route the packet through the network to its final destination. If the addresses were not unique, there would be no way of knowing where a packet should be delivered to. In a simple network, which is not connected to the Internet, it is enough that the addresses are unique locally within that domain. On the Internet, the IP addresses have to be globally unique. The IP address itself is a fixed length binary identifier. An IPv4 address is 32 bits, and an IPv6 address is 128 bits long. The IP address has two functions in an IP network: it uniquely identifies an interface or a node in the network, and it represents a location in the network topology. The identity is related to the uniqueness of the IP addresses - no other node in the network should have the same address as the node that is identified by a certain address. That address uniquely identifies a single network interface of that node and no other. The location means that the address uniquely identifies a network where the node is within the IP network. The IP address can be divided into two parts; the network prefix and the host identifier, which together make the complete IP address. In the following pages, we will describe in more detail what this means in practice for IPv4 and IPv6. In this section we will have a more in-depth look at the IP addresses. First we will explain the IPv4 addresses, and then IPv6. The focus is on the addresses themselves: what are addresses, how do we represent them, and what kind of different address types exist? 1.4.1 IPv4 Addresses As describe above, an IP address is a fixed length binary field. In IPv4, the IP address field is 32 bits long, thus giving a theoretical address space of 232 = 4 billion addresses. Because a binary bit sequence would be a bit difficult to remember, represent, and tel