M5Q23: Spanning Tree Protocol Flashcards
The original Spanning Tree Protocol (STP) is defined under which IEEE standard?
A. 802.3
B. 802.3D
C. 802.1D
D. 802.11
C. 802.1D
Explanation: Spanning Tree Protocol is defined as part of 802.1D which was publicized in 1990. 802.1D is the MAC bridges standard which includes Bridging and Spanning Tree.
The primary function of Spanning Tree Protocol is to prevent _____________ in Ethernet networks.
A. Congestion
B. Loops
C. Hardware failure
D. Broadcasts
B. Loops
Explanation: STP is a loop avoidance protocol that builds a loop-free topology for Ethernet networks. STP creates a spanning tree within a network of connected layer-2 bridges (or switches), and disables the links that are not part of the spanning tree, leaving only a single active path between any two bridges (or switches) on the network.
Switches exchange ____________ messages with other switches to communicate about STP.
A. Bridge Protocol Data Unit (BPDU)
B. Bridge Priority Down Up (BPDU)
C. Bridge Primary Data Unit (BPDU)
D. Bridge Priority Data Unit (BPDU)
A. Bridge Protocol Data Unit (BPDU)
Explanation: Switches exchange BPDU messages with other switches to build the spanning-tree topology and detect loops.
If a switch has multiple paths to reach the root bridge, it places the port(s) with the least desirable path into which of the following spanning tree port states to ensure only a single active path?
A. Listening
B. Learning
C. Blocking
D. Forwarding
C. Blocking
Explanation: When a switchport is initially connected, Spanning Tree Protocol moves through 4 different port states: Listening, Learning, Blocking and Forwarding. As STP detects a redundant path to another switch it places the port that has the least desirable path into the Blocking state. The port with the most desirable path enters the Forwarding state so that it can pass traffic. When a port is in the Blocking state it will not pass any Frames other than BPDU messages and in effect shuts the port down preventing a loop between the switches.
The switch with the lowest ______________ is elected as the Spanning Tree Root Bridge.
A. MAC Address
B. Bridge ID
C. BPDU
D. IP Address
B. Bridge ID
Explanation: The Bridge ID is made up of the switch MAC Address and the Bridge Priority. If all switches are left at the default settings they will all have the same Bridge Priority value and then the switch with the lowest numbered MAC Address would be elected as the Root Bridge. However, if a switch in the topology has the Bridge Priority value adjusted to a lower value than the other switches then that switch with the lowest Bridge Priority value will be elected.
Rapid Spanning Tree Protocol is faster than traditional Spanning Tree Protocol, has fewer port states and is identified under 802.1W.
A. True
B. False
A. True
Explanation: Rapid Spanning Tree Protocol (RSTP) is an evolution of 802.1D and is originally defined under 802.1W. RSTP has faster spanning tree topology convergence time and only three port states (Discarding, Learning, Forwarding).
You connect a workstation to a port on a switch. You notice the link light on the switch port is colored amber for around 30 seconds and during that time the workstation is still not fully connected. Thankfully the link light turns green after the 30 seconds and the workstation is then able to communicate with the network. What was the cause of this delay and the amber link light?
A. The switch was acting abnormally
B. The workstation network interface card was bad
C. The switch detected a loop
D. The switch port was running through the spanning tree process
D. The switch port was running through the spanning tree process
Explanation: With the default spanning tree settings a switch will go through the process of Listening and Learning before it allows a port to go into the Forwarding state. This process takes around 30 seconds (15 sec for Listening and 15 sec for Learning) and happens even when a regular computer is connected to the switch. Because of this, there is a 30 second delay until the host will come online fully. There are ways to make this happen more quickly such as turning on spanning-tree portfast.
You connect two switches together with redundant connections (two cables connected between the switches). You check the ports on the switches and you see that only one of the connections is active and the other connection is not active. This is because the switches have a problem and are not functioning correctly.
A. True
B. False
B. False
Explanation: This is normal behavior and the proper function of Spanning Tree Protocol. Without this feature both links would be active and there would be a loop between the switches which would cause problems in the network. After the switches are connected STP automatically detects the second connection and disables it.
