ed the routing process. As described earlier, the gateway has an IPv6 address whose prefix (the first part of the address) is common with all the entities in its reference subnetwork. Thus, when searching routing tables, routers need not search a complete correspondence between the destination IP address and the table entry, but a partial correspondence between a prefix of the address and a table entry, that is the gateway address. Since different gateways can have similar addresses, it is possible that more than one prefix correspondence is found. Among them, the longest corresponding prefix has to be chosen since it indicates the correct gateways. Although this procedure allows a better management of IPv6 addresses, it also compli- cates routing table searching. In fact, while the search of a complete correspondence ends when it is found, the fact that a prefix correspondence is found does not stop the prefix match search, since a longer match is always possible. We will come back on this search mechanism and on its implementations in Chapter 7, when analyzing routers architectures and performances. The large number of IPv6 addresses allows also large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. All modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home network- ing routers, multimedia equipment, and network peripherals. 3.2.4 Carrier Class Ethernet The adoption of the architecture of the packet network of the IP model leaves open the choice for the implementation of the packet network layer performing the interface with the transport network, that is, in line with OSI nomenclature, the layer 2 architecture. For the extremely wide diffusion of its LAN version, the Ethernet is a natural candidate to this role, assuring wide compatibility with services (almost all service machines have Ethernet interfaces) and low prices due to the extremely 