IPng must have a viable strategy for migration from, and coexistence with, IPv4. IPv4 and IPng must coexist well, because they will need to do so for several years. IPng, IPng must offer compelling advantages and an easy migration path. Corporate networks must meet promised levels of service while controlling costs through efficient use of resources. Many businesses will not connect to a network until they are confident that it will not significantly threaten the confidentiality, integrity, or availability of their data.
Corporations tend to use multiple protocols.
The IETF needs a strategy for heterogeneity flexible enough to accommodate the principal multiprotocol techniques, including multiprotocol transport, tunneling, and link sharing. The current Internet protocols could be enhanced to satisfy most of the remaining requirements of commercial users while retaining IPv4. As the use of IPv4 continues to grow, the day may come when no more IPv4 network addresses will be left, and no additional networks will be able to connect to the Internet. The hundreds of millions of people on networks that do get IPv4 addresses won't be affected directly by the exhaustion of the address space, but they will miss the opportunity to communicate with those less lucky. Because the Internet is too large for all its users to cutover to IPng quickly, IPng must coexist well with IPv4.