IPv6 over IPv4 Manual Tunnel

An IPv6 over IPv4 manual tunnel is manually created and configured on the border routers on both ends of the tunnel. To configure this tunnel, you must specify static source and destination IPv4 addresses.

The manual tunnel serves the communication between IPv6 islands and the communication between a border router and a host. The end-point devices of the tunnel must support IPv6/IPv4 dual stacks. Other devices only need to support single protocol stacks.

Figure 1 IPv6 over IPv4 manual tunnel

As shown in Figure 1, when host A connects to host B, the processing procedures are as follows:

1. The IPv6 packet sent by host A arrives at FW_A.
2. FW_A searches the IPv6 forwarding table based on the destination IP address of the IPv6 packet and discovers that the packet is forwarded by the tunnel interface.
3. FW_A encapsulates the IPv6 packet with an IPv4 packet header. The destination IP address in the IPv4 packet header is the source IPv4 address specified by the peer end of the tunnel, and the source IP address is the source IPv4 address specified by the local end of the tunnel. After the encapsulation, the packet is forwarded by FW_A from the tunnel interface and then routed to the destination, namely, FW_B on the IPv4 network.
4. After receiving the IPv4 packet, FW_B decapsulates it, searches for a route based on the destination IP address of the IPv6 packet, and then sends the IPv6 packet to host B.
5. Host B receives and responds to the packet. The response packet is processed in the same way.