Book excerpt from IPv6 for Enterprise Networks

Chapter 3: Common IPv6 Coexistence Mechanisms

As the name suggests, transition mechanisms help in the transition from one protocol to another. In the perspective of IPv6, transition basically means moving from IPv4 to IPv6. One day, IPv6 networks will completely replace today’s IPv4 networks. For the near term, a number of transition mechanisms are required to enable both protocols to operate simultaneously. Some of the most widely used transition mechanisms are discussed in the following sections.


Dual-stack is the foundational and preferred IPv4-to-IPv6 transition mechanism. Dual-stack provides the most natural way for IPv6 hosts and networks to be deployed because no tunneling or translation needs to be performed for end-to-end connectivity. In a dual-stack deployment, both IPv4 and IPv6 are operational on all components (hosts, servers, routers, switches, firewalls, and so on) attached to the network.

The dual-stack mechanism has been used in the past. Previous examples of this mechanism include IPv4 with IPX and/or AppleTalk coexisting on the same node. As with other uses of dual-stack, the IPv4 and IPv6 protocols are not compatible with each other.

The dual-stack model enables the smoothest transitioning from IPv4 to IPv6 environments with minimal service disruptions. This model works by enabling IPv6 in the existing IPv4 environments along with the associated features required to make IPv6 routable, highly available, and secure.

The primary advantage of the dual-stack mechanism is that it does not require tunneling within the network. The dual-stack runs the two protocols as "ships-in-the-night," meaning that IPv4 and IPv6 run alongside one another and have no dependency on each other to function, except that they share network resources. Both IPv4 and IPv6 have independent routing, high availability (HA), quality of service (QoS), security, and multicast policies. Dual-stack also offers forwarding performance advantages because packets are natively forwarded without requiring additional encapsulation and lookup overhead.

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