Hence more than 200 trillion blocks of a lot many trillions more unique addresses are possible for allocation. This unique advantage equips ISPs, Govts, MNCs and Universities to allocate themselves virtually unlimited address space ushering the sustained growth of the Internet helping online transaction more secure. IPv6 also provides several enhancements to the present Internet experience over its previous avatar which seems impossible within the present IPv4 framework. Embedded security features and optimised transmission of huge amounts of data, the maximum expected characteristics of IPv6 is all set to transform the Internet into a secured universe and lend the user an experience where enriched content can be distributed and consumed. (Johnson, 2011) Transitioning challenges to IPv6 confronting industry and Govt:

In changing over to IPv6, immediate costs are associated that varies according to network needs and business. The cost differences depend on network infrastructure, types of services, and future requirements of an enterprise's network and the level of security needed during the switchover. Besides, deploying IPv6 involves configuration, testing, management costs, software costs and hardware upgrades which can also impact the profitability of industry. In case of a lot of enterprises, operational...

In case of enterprises that operate customized software developed as an in-house practice will also incur additional costs in order to upgrade those particular programs to IPv6. (Abuquayyas, 2009)
One of the major drawbacks of this transitioning is that IPv6 is not backwards compatible with IPv4 as the two protocols operate on different bits i.e. IPv4 on 32 bits while IPv6 on 128 bits. Hence to avoid that, the two protocols must be deployed or improved tunneling and translation systems installed for seamless functioning. Moreover dual existence of IPv4 and IPv6 will be a major challenge for IPv6 and IPv4 will require supporting alongside IPv6 for a consistent time period. (Abuquayyas, 2009)

References

Abuquayyas, Abdelfattah. (2009) "Transition to IPv6: Drivers and Challenges -- Chapter:

IPv Challenges" Workshop on the IPv6 development in Saudi Arabia, Communications and Information Technology Commission.

You +1'd this publicly. Undo Johnson, Christopher. (2011) "Transitioning to IPv6: The Next Generation Internet"

Retrieved 14 November, 2012 from https://classes.lt.unt.edu/Fall_2011/LTEC_4550_020/csj0045/Transitioning%20to%20IPv6.pdf