H3C Technologies H3C S12500-X Series Switches - Manual (Page 145)

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Configuring tunneling
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, IPv4 over IPv4,
IPv4 over IPv6, and IPv6 over IPv6 tunnels.
IPv6 over IPv4 tunneling
Implementation
IPv6 over IPv4 tunneling enables isolated IPv6 networks to communicate, as shown in Figure 49 .
NOTE:
The devices at the ends of an IPv6 over IPv4 tunnel must support the IPv4/IPv6 dual stack.
Figure 49 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