Combination of Port Types on RSTP Root Bridge

C

In an RSTP (Rapid Spanning Tree Protocol) network, there are four types of ports that a switch can have:

1. Root Port: The port that offers the lowest path cost towards the root bridge.
2. Designated Port: The port that is in charge of forwarding data on a segment towards the root bridge.
3. Alternate Port: The port that is a backup for a designated port, in case the designated port fails.
4. Backup Port: The port that is a backup for the root port, in case the root port fails.

The root bridge in an RSTP network is the switch that has the lowest bridge ID. The bridge ID is a combination of a priority value and the switch's MAC address.

Now, coming back to the question, the answer is (C) "All ports will be designated ports" because the root bridge in an RSTP network only has designated ports.

When a switch becomes the root bridge, all its ports become designated ports, and it starts forwarding data to all the other switches in the network. All other switches will have a combination of root ports, designated ports, alternate ports, and backup ports, depending on their location in the network.

Therefore, Option (A) "There can be some combination of designated ports and backup ports" and Option (B) "There can be some combination of root ports and alternate ports" are incorrect. Option (D) "All ports will be root ports" is also incorrect because the root bridge does not have any root ports; it only has designated ports.