Quality of Service and performance characterization of IPv6 relative to IPv4

III.3.3.2 Tunneling Transition Mechanism

Configured tunneling provides a means to carry IPv6 packets over unmodified IPv4 routing infrastructures.

Tunneling can be used to deploy an IPv6 forwarding infrastructure while the overall IPv4 infrastructure is still the basis.

Tunneling can be also used to carry IPv6 traffic by encapsulating it in IPv4 packets and tunneling it over the IPv4 routing infrastructure.

For instance, if an ISP still has an IPv4-only infrastructure, tunneling allows you to have a corporate IPv6 network and tunnel through your ISP's IPv4 network to reach other IPv6 hosts or networks.

Tunneling techniques is used to avoid order dependencies when upgrading hosts, or routers.^37(*)

The figure below shows how tunneling works.

Figure 4: Tunneling

Source: IPv6 essentials, O'REILLY, ISBN: 0-596-00125-8, page 170

IPv6 node 1 on an IPv6 network wants to send an IPv6 packet to another IPv6 node 2 on another IPv6 network. The network between the two IPv6 nodes is an IPv4 network only.

1. IPv6 node 1 sends an IPv6 packet to Router1.

2. When router 1 receives the packet address, it encapsulates the IPv6 packet in an IPv4 header and forwards it to router 2.

3. Router 2 decapsulates the packet and forwards it to its final destination (the IPv6 node 2)

* ³⁷ IPv6 essentials, O'REILLY, ISBN: 0-596-00125-8, page 170