Which bit indicates whether a MAC address is universally or locally administered?

The correct answer is the 7th bit of the first byte in the MAC address. In a MAC address, the first byte is divided into two parts: the first three bits indicate the Organizationally Unique Identifier (OUI), while the last five bits of that byte are used for the individual address.

The 7th bit, also known as the "locally administered" bit, plays a crucial role in determining whether the MAC address is universally administered (assigned by a manufacturer) or locally administered (assigned by a network administrator). When this bit is set to 0, it indicates that the MAC address is universally administered, meaning it was assigned by the manufacturer and is unique across the network. Conversely, when this bit is set to 1, it indicates that the MAC address is locally administered, allowing for custom MAC addresses to be assigned within a specific network.

Understanding this distinction is important for network design and implementation, ensuring that MAC addresses do not conflict across devices. It also helps in scenarios where devices need a custom identification on a local network.