Routing IPv6 Traffic over IPv4 Infrastructure

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To route IPv6 traffic over an IPv4 infrastructure, the most common technique is 6 to 4 tunneling.

In 6 to 4 tunneling, a dual-stack router creates a tunnel between two IPv6 networks over the IPv4 infrastructure. The tunnel uses the IPv4 addresses of the two routers at either end of the tunnel as the endpoints, and it encapsulates the IPv6 packets inside IPv4 packets for transmission across the IPv4 infrastructure.

The 6 to 4 tunneling technique uses the reserved IPv6 prefix 2002::/16 to indicate that the packet is being tunneled over an IPv4 network. The first 16 bits of the IPv6 address represent the 6 to 4 prefix (2002::/16), the next 32 bits represent the IPv4 address of the router that encapsulates the IPv6 packet, and the remaining 64 bits represent the IPv6 address of the destination network.

For example, if a user on an IPv6 network with the address 2001:DB8:1234::/64 wants to communicate with a user on another IPv6 network with the address 2001:DB8:5678::/64, but the two networks are separated by an IPv4 network, a dual-stack router on each end of the IPv4 network can create a tunnel using the 6 to 4 technique. The router at one end of the tunnel encapsulates the IPv6 packet inside an IPv4 packet and forwards it across the IPv4 network to the router at the other end of the tunnel, which decapsulates the IPv6 packet and forwards it to its final destination.

NAT (Network Address Translation) is not an appropriate technique for routing IPv6 traffic over an IPv4 infrastructure because NAT is used to translate private IP addresses to public IP addresses and vice versa, and it is not designed to handle IPv6 traffic.

L2TPv3 (Layer 2 Tunneling Protocol version 3) is a tunneling protocol that is used to encapsulate Layer 2 frames in IP packets, but it is not commonly used for routing IPv6 traffic over an IPv4 infrastructure.

Dual-stack is a technique in which a network node, such as a router or host, is configured with both IPv4 and IPv6 addresses and can communicate with both IPv4 and IPv6 networks. While dual-stack is an important technique for transitioning from IPv4 to IPv6, it is not a technique specifically designed for routing IPv6 traffic over an IPv4 infrastructure.