ed, indicating that the MAC identifier was managed and (supposedly) globally unique. It is worth noting that for privacy and security reasons a node should never generate IID from sensitive yet unique values, such as from International Mobile Equipment CCCCCCUGCCC CCCCCCCCMMMMMMMM MMMMMMMMMMMMMMMM MMMMMMMMMMMMMMMM Figure 3.4 A modified EUI-64 format for IPv6 IID purposes. Deploying IPv6 in 3GPP Networks CCCCCCCC11111111 11111110MMMMMMMM MMMMMMMMMMMMMMMM Figure 3.5 A modified EUI-64 derived from an IEEE 802 48-bit MAC identifier. Identity (IMEI), Mobile Station International Subscriber Directory Number (MSISDN), or International Mobile Subscriber Identity (IMSI). 3.1.7 IPv6 Address Space Allocations History has proven that no matter the size of the resource, it is always possible to exhaust it with mismanagement and wasteful use. IPv6 provides enormous address space that will be plentiful and will last for a long time, but only if used wisely. At the highest level the Internet Assigned Number (IANA) manages the use of the address pool. As of today, the IPv6 address space is divided into sections listed in Figure 3.6, which also shows a pie chart illustration of the part of the IPv6 address space that is currently reserved for the unicast address space, reserved for the future, and used for various IPv6 uses such as multicast, link-local addressing, ULA, deprecated site-local use, loopback, and SO forth. 3.1.8 Special IPv6 Address Formats The 128 bits used for IPv6 address is long enough to allow for embedding additional infor- mation into the address. Perhaps the most popular piece of information that is embedded into an IPv6 address is an IPv4 address. In particular, various IPv6 transition mechanisms 0.78% 0.39 9 % 0.39 % 0.10% IPv6 address space high level allocations: 0000::/8 Reserved by IETF 0100::/8 Reserved by IETF 12.50% Reserved for the future (85.84%) 0200::/7 Reserved by IETF 0400::/6 Reserved by IETF 0800::/5 Reserved by IETF Global unicast (12.50%) 1000::/4 Reserved by IETF 2000::/3 Global Unicast 40