Which action must be taken to assign a global unicast IPv6 address on (CCNA 200-301)

Correct answer: C) enable SLAAC on an interface.
Here's a breakdown of why the other options are incorrect:

A - explicitly assign a link-local address:

Link-local addresses are automatically generated for each IPv6 interface, they don't require explicit assignment.
They're used for communication within the local network segment, not for global unicast addresses.
B - disable the EUI-64 bit process:

EUI-64 is the mechanism that derives the interface ID from the MAC address, which is essential for SLAAC to create a global unicast address.
Disabling EUI-64 would hinder the process of generating the address.
D - configure a stateful DHCPv6 server on the network:

Stateful DHCPv6 servers can assign IPv6 addresses, but they don't derive the interface ID from the MAC address.
They allocate addresses from a pool and assign them to devices based on their requests.
Here's how SLAAC works to assign a global unicast IPv6 address derived from the MAC address:

Router Advertisements: The router sends Router Advertisement (RA) messages that contain information about the network prefix and configuration flags, including whether SLAAC is enabled.
Interface ID Generation: The device uses EUI-64 to create a 64-bit interface ID from its MAC address.
Address Formation: The device combines the network prefix from the RA message with the generated interface ID to form a complete global unicast IPv6 address.
Duplicate Address Detection (DAD): The device performs DAD to ensure the address is unique on the network before using it.
Key points to remember:

SLAAC is a stateless process, meaning it doesn't require a server to manage address assignments.
It's a simple and efficient way to configure IPv6 addresses on devices, especially in large networks.
However, it might not be suitable for environments where centralized control over address allocation is required.