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/>Authentication and Privacy Capabilities

Interface IDs
IPv6 addresses are 128-bits long, however the bottom 64 bits of the address is devoted to identifying a particular machine within a subnet. This part is known as the interface ID, and is commonly derived from a host's Ethernet MAC address. Note that it's not compulsory to use an interface ID derived from an Ethernet address. As long as the global/local bit (::0200:0000:0000:0000) isn't set, it's permitted to invent one's own interface ID, just as in IPv4.

IPv6 Addressing
IPv6 addresses are 128-bits long and are identifiers for individual interfaces and sets of interfaces. IPv6 Addresses of all types are assigned to interfaces, not nodes. Since each interface belongs to a single node, any of that node's interfaces' unicast addresses may be used as an identifier for the node. A single interface may be assigned multiple IPv6 addresses of any type.
There are three types of IPv6 addresses. These are unicast, anycast, and multicast. Unicast addresses identify a single interface. Anycast addresses identify a set of interfaces such that a packet sent to a anycast address will be delivered to one member of the set. Multicast addresses identify a group of interfaces, such that a packet sent to a multicast address is delivered to all of the interfaces in the group. There are no broadcast addresses in IPv6, their function being superseded by multicast addresses.

IPv6 supports addresses which are four times the number of bits as IPv4 addresses (128 vs. 32). This is 4 Billion times 4 Billion times 4 Billion (2^^96) times the size of the IPv4 address space (2^^32). This works out to be:
340,282,366,920,938,463,463,37 4,607,431,768,211,456

IPv6 Routing
Routing in IPv6 is almost identical to IPv4 routing under CIDR except that the addresses are 128- bit IPv6 addresses instead of 32-bit IPv4 addresses. With very straightforward extensions, all of IPv4's routing algorithms (OSPF, RIP, IDRP, ISIS, etc.) can be used to route IPv6.

IPv6 also includes simple routing extensions which support powerful new routing functionality. These capabilities include:
Provider Selection (based on policy, performance, cost, etc.)
Host Mobility (route to current location)
Auto-Readdressing (route to new address)
The new routing functionality is obtained by creating sequences of IPv6 addresses using the IPv6 Routing option. The routing option is used by an IPv6 source to list one or more intermediate nodes (or topological group) to be "visited" on the

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