In RSTP, which of the following ports are not put in the forwarding state?

Hi simon.waweru,

I think the answer is CD.

Alternate Port (AP, alternate port): a blocked switch port, which does not forward data frames or fill the MAC address table with the source MAC address of the received frame, but can forward BPDU frames. From the perspective of sending configuration BPDUs, a substitute port is a port that is blocked because it learns configuration BPDUs sent by other bridges. From a user traffic perspective, the alternate port provides another switchable path from the designated bridge to the root bridge as a backup port for the root port.

Backup port (BP): a blocked switch port. It does not forward data frames or fill the MAC address table with the source MAC addresses of received frames, but can forward BPDU frames. From the perspective of sending configuration BPDUs, the backup port is the port that is blocked because it learns the configuration BPDUs sent by itself. From the perspective of user traffic, the backup port provides another backup path from the root node to the leaf node, which serves as the backup of the specified port.