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• IPv6 over IPv4 manual tunneling—A point-to-point link. This type of tunneling provides the
following solutions:
{ Connects isolated IPv6 networks over an IPv4 network.
{ Connects an IPv6 network and an IPv4/IPv6 dual-stack host over an IPv4 network.
• Automatic IPv4-compatible IPv6 tunneling—A point-to-multipoint link. Automatic
IPv4-compatible IPv6 tunnels have limitations because IPv4-compatible IPv6 addresses must
use globally unique IPv4 addresses.
• 6to4 tunneling
{ Ordinary 6to4 tunneling—A point-to-multipoint automatic tunnel. It is used to connect
multiple isolated IPv6 networks over an IPv4 network.
6to4 tunneling uses an IPv4 address to identify a 6to4 network. This method overcomes the
limitations of automatic IPv4-compatible IPv6 tunneling.
{ 6to4 relay—Connects a 6to4 network and an IPv6 network that uses an IP prefix other than
2002::/16. A 6to4 relay router is a gateway that forwards packets from a 6to4 network to an
IPv6 network.
As shown in Figure 115, 6to4 net
work Site 1 communicates with IPv6 network Site 3 over a
6to4 tunnel. Configure a static route on the border router (Device A) in the 6to4 network.
The next hop address must be the 6to4 address of the 6to4 relay router (Device C). Device
A forwards all packets destined for the IPv6 network over the 6to4 tunnel, and Device C
then forwards them to the IPv6 network.
Figure 115 Principle of 6to4 tunneling and 6to4 relay
• ISATAP tunneling—A point-to-multipoint automatic tunnel. It provides a solution to connect an
IPv6 host and an IPv6 network over an IPv4 network. ISATAP tunnels are mainly used for
communication between IPv6 routers or between an IPv6 host and an IPv6 router over an IPv4
network.
Figure 116 Principle of ISATAP tunneling
IPv4 over IPv4 tunneling
IPv4 over IPv4 tunneling (RFC 1853) enables isolated IPv4 networks to communicate. For example,
an IPv4 over IPv4 tunnel can connect isolated private IPv4 networks over a public IPv4 network.
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