upply 75 IP addresses to every square inch of the earth's surface, including oceans! IPv6 addresses typi- cally have two parts: a 64-bit network prefix and a 64-bit host address. The host address can be assigned sequentially or automatically generated from the inter- face's MAC address. The IPv6 addressing structure uses hexadecimal notation, normally written as eight groups of four hexadecimal digits, and colons replace the periods used in IPv4, as in the following example: 2001:0db8:85a3:0000:1319:8a2e:0370:7344 IPv6 has four address types: unicast (one-to-one), anycast (one-to-nearest), multicast (one-to-many), and a reserved class. A single interface may be assigned multiple IPv6 addresses of unicast, anycast, or multicast addresses. Note that IPv6 does not support broadcasting. IPv6 is designed to be an evolutionary step from IPv4. It can be installed as a normal software upgrade in Internet devices and is interoperable with IPv4. IPv6 runs well in high-performance networks, such as Gigabit Ethernet and ATM net- works, and it is also efficient for low-bandwidth networks such as wireless networks. In addition, it provides a platform for new Internet functionality that will be required in the near future. IPv6 simplifies the packet header format (see Figure 8.14). It Chapter 8 The Internet and IP Infrastructures Version Traffic Class Flow Label 4 Bits 8 Bits 20 Bits Payload Length Next Header Hop Limit 16 Bits 8 Bits 8 Bits Source Address 128 Bits Destination Address 128 Bits Figure 8.14 The IPv6 packet header supports autoconfiguration and multihoming. IPv6 includes the DiffServ Code Point (DSCP) in the traffic class, and it addresses authentication and privacy capabilities. Benefits of IPv6 include improved routing efficiency due to the streamlined header format as well as simplified administration. QoS capabilities are also enhanced because the specification includes a flow label to support real-time traf- fic. Finally, IPv6 offers better security mechanisms, mandating the use of IPsec and IKE (which are di