Practice Q's - RTSP Flashcards
Which of the following standards describes the details of RSTP?
A. 802.1d
B. 802.1w
C. 802.1s
D. 802.1x
Answer: B
Explanation:
Rapid Spanning Tree Protocol (RSTP) is described in the IEEE 802.1w standard. It has several enhancements over Spanning Tree Protocol (STP), which uses 802.1d. The result of these enchantments is a more rapid convergence when topology changes occur. The two protocols can coexist in the network.
If a switch running RSTP receives an 802.1d Bridge Protocol Data Unit (BPDU), on a port it will begin to use 802.1d rules on that port. However, the IEEE 802.1d standard describes STP and not RSTP.
The IEEE 802.1s standard describes Multiple Spanning Tree Protocol (MST). This enhancement allows for multiple instances of STP. Unlike Common Spanning Tree Protocol (802.1q) and Per- VLAN Spanning Tree Protocol Plus (PVST+), which allow for a single instance of STP or an instance for every VLAN, respectively, MST allows the administrator to map several VLANs to the same instance, without committing them all to the same instance.
IEEE 802.1x describes a standard for port-based access control. It is not related to VLANs or their management.
What are the three RSTP port states? (Choose three.)
A. Initializing
B. Blocking
C. Learning
D. Listening
E. Forwarding
F. Discarding
Answer: C,E,F
Explanation:
Rapid Spanning Tree Protocol (RSTP) uses only three port states: discarding, learning, and forwarding. The learning and forwarding states are the same as the original STP standard, but the discarding state performs the functions originally performed in the disabled, blocking, and listening STP states.
With STP, you can safely assume that a listening port is either designated or root, and is on its way to the forwarding state. Unfortunately, once a port is in the forwarding state, there is no way to tell whether the port is root or designated. There is no difference in the operation of a port in blocking state and a port in listening state, since they both discard frames and do not learn MAC addresses. The real difference is in the role the spanning tree assigns to the port. RSTP decouples the role and the state of a port.
With RSTP, a role is assigned to a port. The root port and designated port roles are the same as with STP, while the blocking port role is split into the backup and alternative port roles. The Spanning Tree Algorithm (STA) determines the role of a port based on Bridge Protocol Data Units (BPDUs). The RSTP roles can be defined as follows:
Ports on the switch can also be classified as edge ports and non-edge ports. Access ports or edge ports are those that attach to devices such as workstations or printers. Non-edge ports are those that connect to other switches. If a non-edge port transitions to a forwarding state, a TC BPDU will be generated. On the other hand, when an edge ports transitions to the forwarding state, such as after a computer boots up or a device is connected to the port, no TC BPDU is generated.
With RSTP hello timers set to the default interval, how quickly can a non-edge port discover that its neighbor is down?
A. 20 seconds
B. 10 seconds
C. 6 seconds
D. 5 seconds
Answer: C
Explanation:
With Rapid Spanning Tree Protocol (RSTP) hello timers set at the default interval, a non-edge port can discover that its neighbor is down in 6 seconds. One of the advantages of RSTP over STP is quicker convergence when changes occur in the topology. After a non-edge port fails to receive three Bridge Protocol Data Units (BPDUs) from its neighbor, it will assume the neighbor to be down and will age out all information regarding the neighbor. Since hellos are sent at 2-second intervals in RSTP, it will take only 6 seconds for this to occur, as compared to 20 seconds for STP.
All other options are incorrect values for the default convergence time for RSTP.
