3Com Switch 4800G 24-Port Configuration Manual page 524

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HAPTER UNNELING
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ONFIGURATION
Figure 157 Principle of IPv6 over IPv4 tunnel
IPv6 header IPv6 data
IPv6 network
Dual stack router
IPv6 host
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 the IPv6 packet with an IPv4 header the 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 destination device forwards the packet according to the destination address in
the decapsulated IPv6 packet. If the destination address is the device itself, the
device 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.
If the IPv4 address of the tunnel destination cannot be acquired from the
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destination address of the IPv6 packet, it needs to be configured manually.
Such a tunnel is called a configured tunnel.
If the IPv4 address is embedded into the IPv6 address, the IPv4 address of the
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tunnel destination can automatically be acquired from the destination address
of the IPv6 packet. Such a tunnel is called an automatic tunnel.
Type
According to the way an IPv6 packet is encapsulated, IPv6 over IPv4 tunnels are
divided into the following types:
IPv6 manual tunnel
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6to4 tunnel
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ISATAP tunnel
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IPv4 header IPv6 header
IPv4 network
IPv6 over IPv4 tunnel
IPv6 data
IPv6 header
IPv6 network
Dual stack router
IPv6 host
IPv6 data