HP-UX IPv6 Transport Administrator's Guide for TOUR 2.0 (April 2004, rev 2)

IPv6 Software and Interface Technology
Migrating from IPv4 to IPv6
Chapter 772
Migrating from IPv4 to IPv6
IPv6 is the next generation Internet protocol and is designed to be a
replacement for IPv4. However, it is expected that IPv6 adoption will be
gradual and there will be a lengthy transition period during which IPv4
and IPv6 protocols will have to coexist. The IETF (ngtrans working
group) has developed a number of transition mechanisms that facilitates
IPv6 deployment.
The main goals of these transition mechanisms are to allow newly
deployed IPv6 hosts and routers to inter-operate with existing IPv4 hosts
and routers and allow isolated IPv6 hosts and routers to communicate
with each other using the existing IPv4 infrastructure.
TOUR 2.0 supports the following three transition mechanisms:
• Dual stack: This mechanism provides complete concurrent support
for both IPv4 and IPv6 protocols in hosts and routers. It allows
networks to support both IPv4 applications and IPv6 applications.
• Tunneling: Tunneling encapsulates IPv6 packets within IPv4
packets. IPv6 transmission across the IPv4 network is transparent.
On TOUR 2.0 configured (point-to-point) tunneling is supported. In
addition to IP6-in-IP tunneling support, TOUR 2.0 also supports
IP6-in-IP6 and IP-in-IP6 tunnels.
• “6to4”: Isolated IPv6 nodes and networks can communicate over an
IPv4 network, without explicitly configuring tunnels, by using the
“6to4” mechanism (RFC 3056). “6to4” effectively treats the IPv4 wide
area network as a unicast point-to-point link layer. “6to4” requires no
end-node reconfiguration and minimal router configuration.
Tunneling
Tunneling enables IPv6 hosts and routers to connect with other IPv6
hosts and routers over an existing IPv4 network. Dual stack hosts and
routers can tunnel IPv6 packets over regions of IPv4 routing topology by
encapsulating them within IPv4 packets. The encapsulated packets
travel across an IPv4 Internet until they reach their destination host or
router. The IPv6-aware host or router decapsulates the IPv6 datagrams,
forwarding them as needed. The IPv6 transmission across the IPv4
Internet is transparent. This type of tunneling is referred to as IP6-in-IP.