H3C Technologies H3C S10500 Series Switches - Manual (Page 162)

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IPv4 over IPv6 tunneling
Introduction
IPv4 over IPv6 tunneling adds an IPv6 header to IPv4 packets so that the IPv4 packets can traverse an
IPv6 network and reach another IPv4 network.
Encapsulation and de-encapsulation
Figure 68 Principle of IPv4 over IPv6 tunneling
The encapsulation and de-encapsulation processes illustrated in Figure 69 are described as follows:
• Encapsulation
1. Upon receiving a packet from the attached IPv4 network, Device A examines the destination
address of the packet and determines the outgoing interface.
2. If the packet is destined for the IPv4 network attached to Device B, Device A delivers the packet to
the tunnel interface pointed to Device B.
3. The tunnel interface adds an IPv6 header to the original IPv4 packet and delivers the packet to the
IPv6 protocol stack for forwarding.
• De-encapsulation
1. Upon receiving a packet from the attached IPv6 network, Device B delivers the packet to the IPv6
protocol stack to examine the protocol type encapsulated in the data portion of the packet.
2. If the protocol type is IPv4, the IPv6 protocol stack delivers the packet to the tunneling module.
3. The tunneling module removes the IPv6 header and delivers the remaining IPv4 packet to the IPv4
protocol stack for subsequent forwarding.
IPv4 over IPv6 tunnel modes
IPv4 over IPv6 tunnels fall into the following modes:
• IPv4 over IPv6 manual tunnel
In this tunnel mode, you must manually configure the source and destination IPv6 addresses for the tunnel.
An IPv4 over IPv6 manual tunnel is a point-to-point virtual link.
• IPv4-over-IPv6 GRE tunnel
The IPv4 over IPv6 GRE tunnel is also a point-to-point virtual link and the source and destination IPv6
address for the tunnel are also manually configured. The difference is that, in the case of manual tunnel,
IPv4 packets are encapsulated by using the IPv6 header, whereas in the case of GRE tunnel, IPv4 packets
are encapsulated based on standard GRE protocol.