Tunnels in the Combined IPv6 and IPv4 Network Environments

Many sites that have IPv6 domains might need to communicate with other IPv6 domains by traversing IPv4 networks during the early phases of IPv6 deployment. The following figure illustrates the tunneling mechanism (indicated by "R" in the figure) between two IPv6 hosts through IPv4 routers.

Figure 4-1  IPv6 Tunneling Mechanism

In the previous figure, the tunnel consists of two routers that are configured with a virtual point-to-point link between the two routers over the IPv4 network.

An IPv6 packet is encapsulated within an IPv4 packet. The boundary router of the IPv6 network sets up a point-to-point tunnel over various IPv4 networks to the boundary router of the destination IPv6 network. The packet is transported over the tunnel to the destination boundary router, where the packet is decapsulated. The router then forwards the separate IPv6 packet to the destination node.