Once you have your IPv6 network set up, you will want to connect to other IPv6 networks. However your packets may have to traverse a section of the Internet that does not support IPv6 yet. Does your ISP support IPv6? Does their provider? The real question is do all the routers between you and the target support IPv6?
RFC 1933 discusses transition from IPv4 to IPv6 and coexistence of the two protocols for as long as is required. It is quite possible that small sites may stay on IPv4 and never move to IPv6. Eventually IPv4 will become a legacy system. However you will not be able to access IPv6 only sites.
To transmit an IPv6 packet over IPv4 only hops, the IPv6 packet is encapsulated in an IPv4 header and routed as a normal IPv4 packet. At some stage it will hit an IPv6 capable host/router and will be decapsulated, revealing the original IPv6 packet. This is called "tunnelling".
To test IPv6 implementations and allow sites to communicate, a network called the 6bone has been set up. The 6bone consists of a series of backbone IPv6 sites who handle the internal IPv6 routing. Hanging off these backbone sites are transit and leaf sites. A transit site provides tunnelling support for leaf sites but is not directly on the backbone. A leaf site can connect to a transit site or to a backbone site, in both cases using IPv6 in IPv4 tunnelling.
There are no Australian backbone or transit sites at the moment, there are only two leaf sites. Robert Elz is building an IPv6 site, this may be available for transit or backbone in the future.
© Keith Owens O. C. Software P/L 1997