With the emergence of IPv6 many enterprises are leveraging their IPv4 presence to communicate IPv6 routing information. With BGP, you could do IPv4 over IPv6, IPv6 over IPv4, IPv4 over IPv4, or IPv6 over IPv6. Remember that when you are doing IPv6 over IPv4, think of IPv4 as your transport (like a bus or a truck!) and IPv6 as your passenger protocol (like a passenger on a bus or truck). In other words, IPv4 is responsible for passing around and sharing the IPv6 routing information. This video goes over all the finer points of how to configure BGP when you are doing IPv6 over IPv4!