| Exam 200-120 | Question id=88 | LAN Switching Technologies |
Which statements regarding RSTP are correct?
| A. |
RSTP cannot operate with PVST+. | |
| B. |
RSTP defines new port roles. | |
| C. |
RSTP defines no new port states. | |
| D. |
RSTP is a proprietary implementation of IEEE 802.1D STP. | |
| E. |
RSTP is compatible with the original IEEE 802.1D STP. |
Port Roles
The role is now a variable assigned to a given port. The root port and designated port roles remain, while the blocking port role is split into the backup and alternate port roles. The Spanning Tree Algorithm (STA) determines the role of a port based on Bridge Protocol Data Units (BPDUs). In order to simplify matters, the thing to remember about a BPDU is there is always a method to compare any two of them and decide whether one is more useful than the other. This is based on the value stored in the BPDU and occasionally on the port on which they are received. This considered, the information in this section explains practical approaches to port roles.
Compatibility with 802.1D
RSTP is able to interoperate with legacy STP protocols. However, it is important to note that the inherent fast convergence benefits of 802.1w are lost when it interacts with legacy bridges.