k) (Dual Stack) Figure 8.17 6to4 IPv6 address identifies the IPv4 tunnel endpoints. Border routers need a default route to a 6to4 relay router, or they must run IPv6 interdomain routing protocols (such as MP-BGP). 6to4 can use special anycasts adver- tised by 6to4 relay routers to find the nearest one. The Status of IPv6 Deployment The push to IPv6 was initially driven by a concern that the supply of available addresses would soon run out and that the addressing scheme had to be changed to allow for more addresses. However, especially in the United States, this shortage has not yet been realized. Most large enterprises have address blocks SO big that they have never felt any address crunch at all. Furthermore, CIDR, NAT, network address port translation, and similar technologies have helped ease the strain on IP addresses. Fears about imminent IP address depletion were somewhat exaggerated. Nevertheless, Asia, especially China, is currently experiencing significant difficulty with IP address allocations. All of China has fewer IP addresses allocated to it than does Stanford University. Europe's IP address space issues are somewhat less press- ing than Asia's but are still of concern, especially as mobile 3G networks begin to be deployed. In contrast, there is a general sense of complacency about these issues in the United States. Therefore, IPv6 had dropped off the radar screen of U.S. enter- prises for a while, but now, with the government specifying that all federal agencies must deploy IPv6 by 2008, more attention is being focused on how migration to IPv6 will affect enterprises and providers alike. Again, IPv6 has also become a stra- tegic priority in Europe and a pressing issue in Asia. The European Union issued a consultation report on infrastructure for fully distributed mobile and shared applications. This report, which analyzes the devel- opment and deployment of IPv6, states that IPv6 will be of strategic importance to Europe for the next generation of communication systems. Meanwhile, the Japa- Interne