18 - Questions - Spanning Tree Protocol (STP)
In network design, can you include physical loops between switches?
Yes, to provide redundancy
Which of these is an STP port state but not an RSTP port state?
listening
Where is RSTP defined?
The correct answer is "IEEE 802.1w." Rapid Spanning Tree Protocol (RSTP), or IEEE 802.1w, is an evolution of STP that provides faster convergence of STP.
Which option identifies the STP bridge priority range?
0 to 65535
Which BID would win election as the root, assuming that the switches with these BIDs were in the same network?
4096:0200.1111.1111
How does Ethernet recognize and eliminate looping of frames?
The correct answer is "It does not." Layer 2 LAN protocols, such as Ethernet, lack a mechanism for recognizing and eliminating endless looping of frames.
Which risk is posed by operating a switched network with redundant paths?
Layer 2 loops
Which switch would win election as the root, assuming that the switches with these MAC addresses and priorities were in the same network?
MAC address 0200.1111.1111, priority 0
Which feature of PVST+ is not available in RSTP?
Per-VLAN STP Instance
What could cause a potential problem when a redundant physical connection exists between two or more switches that share a common network segment?
The correct answer is "Layer 2 loops." If a physical loop on a common network segment is created, then a Layer 2 loop is created also. Layer 2 loops create problems such as MAC table instability, multiple frame transmission, and endless looping of broadcast/multicast/unknown unicast frames.
How does STP prevent forwarding loops at OSI Layer 2?
The correct answer is "port blocking." STP provides a loop-free redundant network topology by placing certain ports in the blocking state.
Which two characteristics does BPDU guard offer? (Choose two.)
The correct answers are: "If BPDU is received, it disables the port," and "Usually used in a combination with PortFast." Other answers are not correct.
Study the figure and choose the two correct statements about STP on this network. (Choose two.)
The correct answers are: "Switch B is elected as root bridge because it has a lower BID than switch A" and "Switch A is a non-root bridge." During the process of electing the root bridge, the switch with the lowest BID is elected the root bridge. If one or more bridges have equally lowest bridge priorities, then the bridge with the lowest MAC address will break the tie and be elected the root bridge.
Which two RSTP port roles have not been changed compared to 802.1D? (Choose two.)
The correct answers are: "root," and "designated." 802.1w and Rapid PVST+ have some different port roles and states. The port roles (and states) of root and designated are unchanged.
What are two PortFast characteristics? (Choose two.)
configured on access ports connected to user device immediate transition to forwarding state
