Implementation

IPv6 over IPv4 tunneling enables isolated IPv6 networks to communicate, as shown in Figure 89.

	NOTE: The devices at both ends of an IPv6 over IPv4 tunnel must support the IPv4/IPv6 dual stack.

The IPv6 over IPv4 tunnel processes packets by using the following steps:

1. A host in the IPv6 network sends an IPv6 packet to Device A at the tunnel source.

2. After Device A receives the IPv6 packet, it processes the packet as follows:

   1. Searches the routing table to identify the outgoing interface for the IPv6 packet.

      The outgoing interface is the tunnel interface, so Device A knows that the packet needs to be forwarded through the tunnel.

   2. Adds an IPv4 header to the IPv6 packet and forwards the packet through the physical interface of the tunnel.

      In the IPv4 header, the source IPv4 address is the IPv4 address of the tunnel source, and the destination IPv4 address is the IPv4 address of the tunnel destination.

3. Upon receiving the packet, Device B de-encapsulates the packet.

4. If the destination address of the IPv6 packet is itself, Device B forwards it to the upper-layer protocol. If it is not, Device B forwards it according to the routing table.