IPv4 is likely to co-exist with IPv6 for some time, so a native dual-stack migration strategy will be the best transition option for most providers. Dual-stack mode allows both IPv4 and IPv6 to run simultaneously over the network, which lets end-user devices communicate via whichever protocol they are equipped for. With dual-stack mode, there is no disruption to the service if a client requests an IPv4 address. Clients that receive both an IPv4 and IPv6 address will prefer to access the IPv6 network, if it’s available. The DNS can determine whether the service is reachable over IPv6 or whether to fall back to IPv4.
Of course, dual-stack provisioning isn’t perfect. Service disruption can occur if you don’t have enough IPv4 addresses to hand out to new subscribers. This is because dual-stack systems require devices to have both an IPv4 and IPv6 address. If this is a problem for you, it may be possible to use a tunneling technique or network address translation (NAT).
However NAT comes with its own set of problems including:
- Impaired quality of service for internal and external systems
- Increased network complexity and fragmentation
- Security concerns multiple subscribers share a single, public IPv4 address
- Difficulty with law enforcement compliance
Despite these issues, you may find it difficult to implement native dual-stack mode without NAT if you continue to delay your IPv6 preparations. The sooner that you can begin handing out IPv6 addresses to new customers, the sooner you will be able to store IPv4 resources to provide addresses to older subscriber devices. This means you need to start your IPv6 transition preparations now –– even if you still have plenty of IPv4 resources.