3Com Switch 8800 Advanced Software V5 Configuration Guide

376 CHAPTER 33: TUNNELING CONFIGURATION
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CAUTION: The devices at both ends of an IPv6 over IPv4 tunnel must support
IPv4/IPv6 dual stack.
Figure 112 Principle of IPv6 over IPv4 tunnel
The IPv6 over IPv4 tunnel processes packets in the following way:
1 A host in the IPv6 network sends an IPv6 packet to the device at the source end of
the tunnel.
2 After determining according to the routing table that the packet needs to be
forwarded through the tunnel, the device at the source end of the tunnel
encapsulates an IPv4 header in the IPv6 packet and forwards it through the
physical interface of the tunnel.
3 The encapsulated packet goes through the tunnel to reach the device at the
destination end of the tunnel. The device at the destination end decapsulates the
packet if the destination address of the encapsulated packet is the device itself.
4 The device at the destination end of the tunnel forwards the packet according to
the destination address in the decapsulated IPv6 packet. If the destination address
is the device itself, the device at the destination end forwards the IPv6 packet to
the upper-layer protocol for processing.
Configured tunnel and automatic tunnel
An IPv6 over IPv4 tunnel can be established between hosts, between hosts and
devices, and between devices. The tunnel destination needs to forward packets if
the tunnel destination is not the eventual destination of the IPv6 packet.
According to the way the IPv4 address of the tunnel destination is acquired,
tunnels are divided into configured tunnel and automatic tunnel.
■ The tunnel destination IPv4 address cannot be acquired from the destination
address of the IPv6 packet and it needs to be configured manually. Such a
tunnel is called configured tunnel.
■ If the tunnel destination is just the eventual destination of the IPv6 packet, an
IPv4 address can be embedded into an IPv6 address so that the IPv4 address of
the tunnel destination can automatically be acquired from the destination
address of the IPv6 packet. Such a tunnel is called automatic tunnel.
IPv6 network
IPv6 over IPv4 tunnel
IPv6 network
IPv6 host IPv6 host
Dual stack router
Dual stack router
IPv4 network
IPv6 header IPv6 data
IPv6 header IPv6 dataIPv4 header
IPv6 header IPv6 data