Which IPv6 transition model should be utilized when two or more independent transition mechanisms are required?

Tunneling (e.g., 6in4, GRE) is a single transition mechanism that encapsulates IPv6 packets within IPv4 headers; it does not by itself combine multiple independent mechanisms.

Dual stack runs both IPv4 and IPv6 natively on devices and is itself one transition mechanism, not a framework for combining multiple mechanisms.

Service block is not a recognized standard IPv6 transition model in Cisco design frameworks.

The hybrid model deliberately combines multiple IPv6 transition techniques - for example, using dual stack on the core while deploying tunneling at branch sites - allowing organizations to apply the most appropriate mechanism to each part of the network simultaneously.

Manual tunneling is a specific single-mechanism approach for point-to-point IPv6-over-IPv4 tunnels and does not encompass multiple transition techniques.