Before now, most networks; if not all, runs on IPv4 infrastructure, especially if your network is using old routers and switches. To upgrade your network to be IPv6 compliant, one or two strategies listed below can be used to implement this process on your network.
1. Dual Stacking: This method of migration enables a network to run both IPv4 and IPv6 protocols simultaneously. This is one of the simplest methods you can use to upgrade on your IPv4 network.
Dual stacking enables you to upgrade your older network devices one after another in other to continue the existing communication.
Cisco IOS Release 12.2(2)T are IPv6-ready. As soon as you configure basic IPv4 and IPv6 on the interface, the interface is dual-stacked and forwards IPv4 and IPv6 traffic on that interface.
How to configure IPv6 Dual Stacking.
To configure dual stacking on a Cisco router in your network, all you have to do is enable IPv6 forwarding and assign an IPv6 address to the router interfaces already configured with IPv4 address.
To enable IPv6 on a Cisco IOS router requires that you use the global configuration command ipv6 unicast-routing. This command enables the forwarding of IPv6 data on your network.