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| 2.9 |  | IPv6 |
| 2.9.1 |  | IP address issues solutions |

This module has shown that IPv4 addressing faces two major issues:

- The depletion of addresses, particularly the key medium-sized space
- The pervasive growth of Internet routing tables

In the early 1990s, CIDR ingeniously built on the concept of the address mask and stepped forward to temporarily alleviate these overwhelming problems. The hierarchical nature of CIDR dramatically improved the scalability of IPv4. Once again, a hierarchical design has proven to be a scalable one.

Yet even with subnetting in 1985, variable length subnetting in 1987, and CIDR in 1993, a hierarchical structure could not save IPv4 from one simple problem. The problem is that there simply are not enough addresses to meet future needs. At roughly four billion possibilities, the IPv4 address space is formidable. However, it will not suffice in a future world of mobile Internet enabled devices and IP addressable household appliances.

Recent short-term IPv4 solutions to the address crunch have been developed. These include RFC 1918, which sets aside private addresses for unlimited internal use, and NAT, which allows thousands of hosts to access the Internet with only a handful of valid addresses.

However, the ultimate solution to the address shortage is the introduction of IPv6 and its 128-bit address. Developed to create a supply of addresses that would outlive demand, IPv6 is on course to eventually replace IPv4. The large address space of IPv6 will provide not only far more addresses than IPv4, but additional levels of hierarchy as well.

> Note: 128 bits allows for 340,282,366,920,938,463, 463,374,607,431,768,211,456 possibilities.

In 1994, the Internet Engineering Task Force (IETF) proposed IPv6 in RFC 1752 and a number of working groups were formed in response. IPv6 covers issues such as the following:

- Address depletion
- Quality of service
- Address autoconfiguration
- Authentication
- Security

It will not be easy for organizations deeply invested in the IPv4 scheme to migrate to a totally new architecture. As long as IPv4, with its recent extensions and CIDR enabled hierarchy, remains viable, administrators will shy away from adopting IPv6. A new IP protocol requires new software, new hardware, and new methods of administration. It is likely that IPv4 and IPv6 will coexist, even within an autonomous system, for years to come.

| Web Links IPv6 http://www.ipv6.org/