H3C Technologies H3C S12500 Series Switches - Manual (Page 168)

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Configuring tunneling
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Overview
Tunneling is an encapsulation technology. One network protocol encapsulates packets of another
network protocol and transfers them over a virtual point-to-point connection. The virtual connection is
called a tunnel. Packets are encapsulated at the tunnel source end and de-encapsulated at the tunnel
destination end. Tunneling refers to the whole process from data encapsulation to data transfer to data
de-encapsulation.
Tunneling supports the following technologies:
• Transition techniques, such as IPv6 over IPv4 tunneling, to interconnect IPv4 and IPv6 networks.
• VPN, such as IPv4 over IPv4 tunneling, IPv4/IPv6 over IPv6 tunneling, GRE, DVPN, and IPsec
tunneling.
• Traffic engineering, such as MPLS TE to prevent network congestion.
Unless otherwise specified, the term tunnel in this document refers to IPv6 over IPv4 tunnels.
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IPv6 over IPv4 tunneling
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Implementation
IPv6 over IPv4 tunneling adds an IPv4 header to IPv6 packets so that IPv6 packets can pass an IPv4
network through a tunnel to realize interworking between isolated IPv6 networks, as shown in
798H
Figure 63 .
NOTE:
The devices at the ends of an IPv6 over IPv4 tunnel must support the IPv4/IPv6 dual stack.
Figure 63 IPv6 over IPv4 tunnel
The IPv6 over IPv4 tunnel processes packets in the following steps:
1. A host in the IPv6 network sends an IPv6 packet to Device A at the tunnel source.
2. After determining according to the routing table that the packet needs to be forwarded through the
tunnel, Device A encapsulates the IPv6 packet with an IPv4 header and forwards it through the