Tunnels / Encapsulation
This is one of the oldest methods to allow traversing networks that do not natively support the desired protocol. Usually tunnels that encapsulate IPv6 packets inside IPv4 packets are used. This allows IPv6 packets to traverse IPv4-only networks, but the reverse is also possible. The original packets are forwarded to a location in the network where they are encapsulated so that they can traverse the segment of the network that does not support the original protocol. After this is done, the packets are extracted and forwarded to their final destination natively.
Manual and automatic tunnels are the most commonly used technique. Manual tunnels must be explicitly configured at a network node, while automatic tunnels are automatically created by certain operating systems. As an example of the first type we can mention the manual tunnels created between two routers or those created by “tunnel brokers”. The most commonly used automatic tunneling mechanisms are 6to4 and Teredo.
Another encapsulation mechanism is the technique known as 6PE / 6VPE, which is used to encapsulate IPv6 traffic in MPLS networks.