Podcast
Questions and Answers
What is the primary goal of Spanning Tree Protocol (STP) in a switched network?
What is the primary goal of Spanning Tree Protocol (STP) in a switched network?
Who invented the original Spanning Tree Protocol and algorithm?
Who invented the original Spanning Tree Protocol and algorithm?
What is the purpose of Spanning Tree Protocol in a network with redundant paths?
What is the purpose of Spanning Tree Protocol in a network with redundant paths?
What is the result of Spanning Tree Protocol selecting the best path in a network?
What is the result of Spanning Tree Protocol selecting the best path in a network?
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What is the standard for Spanning Tree Protocol set by?
What is the standard for Spanning Tree Protocol set by?
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What is the main function of Spanning Tree Protocol in a LAN?
What is the main function of Spanning Tree Protocol in a LAN?
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Why do bridges need to continually understand the topology of the network?
Why do bridges need to continually understand the topology of the network?
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What is a characteristic of Spanning Tree Protocol?
What is a characteristic of Spanning Tree Protocol?
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What is the typical time frame for STP to move from one state to another?
What is the typical time frame for STP to move from one state to another?
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What is the initial state of every port in STP?
What is the initial state of every port in STP?
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What is the primary advantage of RSTP networks?
What is the primary advantage of RSTP networks?
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How does RSTP prevent network loops?
How does RSTP prevent network loops?
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What is the first step in the RSTP algorithm?
What is the first step in the RSTP algorithm?
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How is the root bridge selected in RSTP?
How is the root bridge selected in RSTP?
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What is the purpose of the root port in RSTP?
What is the purpose of the root port in RSTP?
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What determines the port cost in RSTP?
What determines the port cost in RSTP?
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What is an advantage of RSTP over STP?
What is an advantage of RSTP over STP?
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In STP, what happens to the port before entering the forwarding state?
In STP, what happens to the port before entering the forwarding state?
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What is the purpose of MSTP?
What is the purpose of MSTP?
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What is a characteristic of the Listening state in STP?
What is a characteristic of the Listening state in STP?
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What is the result of MSTP enabling VLANs to share STP instances?
What is the result of MSTP enabling VLANs to share STP instances?
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What is standardized by the IEEE within the 802.1Q-2014 report?
What is standardized by the IEEE within the 802.1Q-2014 report?
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What is the Discarding state in STP?
What is the Discarding state in STP?
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What is a benefit of RSTP over STP?
What is a benefit of RSTP over STP?
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What is a distinct feature of PVSTP?
What is a distinct feature of PVSTP?
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What is the primary advantage of RSTP compared to STP?
What is the primary advantage of RSTP compared to STP?
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What happens when a version 0 BPDU is seen in PVRSTP?
What happens when a version 0 BPDU is seen in PVRSTP?
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What is the function of MSTP in a network?
What is the function of MSTP in a network?
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What is the effect of load balancing in PVSTP?
What is the effect of load balancing in PVSTP?
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What is the standard supported by PVRSTP?
What is the standard supported by PVRSTP?
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What is the difference between PVSTP and PVRSTP?
What is the difference between PVSTP and PVRSTP?
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What is a common feature of both PVSTP and PVRSTP?
What is a common feature of both PVSTP and PVRSTP?
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What is the criteria for selecting the root port in a switch?
What is the criteria for selecting the root port in a switch?
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What is the purpose of a designated port in a LAN segment?
What is the purpose of a designated port in a LAN segment?
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What happens to an alternate port when the root port fails?
What happens to an alternate port when the root port fails?
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What is the purpose of a backup port in RSTP?
What is the purpose of a backup port in RSTP?
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What is the number of root ports per non-root switch in RSTP?
What is the number of root ports per non-root switch in RSTP?
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What are Bridge Protocol Data Units (BPDUs) used for?
What are Bridge Protocol Data Units (BPDUs) used for?
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What is the state of a port that is not forwarding traffic and not updating MAC address tables?
What is the state of a port that is not forwarding traffic and not updating MAC address tables?
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What is the relationship between link speed and port cost in RSTP?
What is the relationship between link speed and port cost in RSTP?
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What happens to redundant links in a LAN when STP is enabled?
What happens to redundant links in a LAN when STP is enabled?
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What is the purpose of an algorithm in Spanning Tree Protocol?
What is the purpose of an algorithm in Spanning Tree Protocol?
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What is a characteristic of Spanning Tree Protocol?
What is a characteristic of Spanning Tree Protocol?
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Why is Spanning Tree Protocol necessary in a network with redundant paths?
Why is Spanning Tree Protocol necessary in a network with redundant paths?
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What organization standardized Spanning Tree Protocol?
What organization standardized Spanning Tree Protocol?
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What is the primary function of bridges in a network with redundant paths?
What is the primary function of bridges in a network with redundant paths?
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What is a feature of Spanning Tree Protocol?
What is a feature of Spanning Tree Protocol?
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What is the purpose of Spanning Tree Protocol in a local area network?
What is the purpose of Spanning Tree Protocol in a local area network?
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What is the main reason for STP to balance states across ports?
What is the main reason for STP to balance states across ports?
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What is the role of the root bridge in RSTP?
What is the role of the root bridge in RSTP?
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What happens to a port that has been disabled in STP?
What happens to a port that has been disabled in STP?
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What is the purpose of RSTP in Ethernet networks?
What is the purpose of RSTP in Ethernet networks?
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How is the root port selected in RSTP?
How is the root port selected in RSTP?
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What is the advantage of RSTP over traditional network architectures?
What is the advantage of RSTP over traditional network architectures?
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What is the purpose of blocking redundant paths in RSTP?
What is the purpose of blocking redundant paths in RSTP?
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What determines the port cost in RSTP?
What determines the port cost in RSTP?
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What is the primary advantage of RSTP over STP in terms of convergence time?
What is the primary advantage of RSTP over STP in terms of convergence time?
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What is the purpose of the Listening state in STP?
What is the purpose of the Listening state in STP?
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What does MSTP enable for each VLAN?
What does MSTP enable for each VLAN?
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What is the benefit of MSTP in terms of scalability?
What is the benefit of MSTP in terms of scalability?
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What is the state of a port that is learning MAC addresses but not forwarding traffic?
What is the state of a port that is learning MAC addresses but not forwarding traffic?
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What is the primary advantage of MSTP over STP?
What is the primary advantage of MSTP over STP?
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What is the purpose of MSTP in a network?
What is the purpose of MSTP in a network?
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What is the standardized protocol that MSTP is based on?
What is the standardized protocol that MSTP is based on?
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What is the main advantage of PVSTP in a switched network?
What is the main advantage of PVSTP in a switched network?
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What happens when a version 0 BPDU is seen in PVRSTP?
What happens when a version 0 BPDU is seen in PVRSTP?
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What is the primary function of PVRSTP in a network?
What is the primary function of PVRSTP in a network?
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What is the main difference between PVSTP and PVRSTP?
What is the main difference between PVSTP and PVRSTP?
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What is the advantage of MSTP over STP?
What is the advantage of MSTP over STP?
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What is the purpose of Spanning Tree Protocol in a network with redundant paths?
What is the purpose of Spanning Tree Protocol in a network with redundant paths?
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What is the standard supported by PVRSTP?
What is the standard supported by PVRSTP?
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What is the primary advantage of RSTP over STP?
What is the primary advantage of RSTP over STP?
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What is the primary criterion for selecting the root port in a switch?
What is the primary criterion for selecting the root port in a switch?
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What happens to an alternate port when the root port fails?
What happens to an alternate port when the root port fails?
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What is the purpose of a backup port in RSTP?
What is the purpose of a backup port in RSTP?
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What is the state of a port that is not forwarding traffic and not updating MAC address tables?
What is the state of a port that is not forwarding traffic and not updating MAC address tables?
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How many root ports are there per non-root switch in RSTP?
How many root ports are there per non-root switch in RSTP?
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What is the purpose of a designated port in a LAN segment?
What is the purpose of a designated port in a LAN segment?
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What are Bridge Protocol Data Units (BPDUs) used for?
What are Bridge Protocol Data Units (BPDUs) used for?
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What determines the port cost in RSTP?
What determines the port cost in RSTP?
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What is the purpose of Bridge Protocol Data Units (BPDUs) in a spanning tree protocol?
What is the purpose of Bridge Protocol Data Units (BPDUs) in a spanning tree protocol?
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What is the primary function of a port in the Listening state in STP?
What is the primary function of a port in the Listening state in STP?
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What happens to a port when it transitions from the Listening state to the Learning state in STP?
What happens to a port when it transitions from the Listening state to the Learning state in STP?
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What is the state of a port that has been disabled and then enabled in STP?
What is the state of a port that has been disabled and then enabled in STP?
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What is the main reason for STP to balance states across ports?
What is the main reason for STP to balance states across ports?
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What is the purpose of the Disabled state in STP?
What is the purpose of the Disabled state in STP?
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What is the primary function of a port in the Forwarding state in STP?
What is the primary function of a port in the Forwarding state in STP?
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How does RSTP ensure a loop-free topology in Ethernet networks?
How does RSTP ensure a loop-free topology in Ethernet networks?
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What determines the root bridge in RSTP?
What determines the root bridge in RSTP?
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What happens to a port in the Blocking state in STP?
What happens to a port in the Blocking state in STP?
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What is the primary function of a port in the Learning state in STP?
What is the primary function of a port in the Learning state in STP?
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What is the purpose of the root port in RSTP?
What is the purpose of the root port in RSTP?
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What happens to the address table in the Forwarding state in STP?
What happens to the address table in the Forwarding state in STP?
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What is the relationship between link speed and port cost in RSTP?
What is the relationship between link speed and port cost in RSTP?
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What happens to all interfaces on the root bridge in RSTP?
What happens to all interfaces on the root bridge in RSTP?
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What is the benefit of RSTP over STP in terms of network availability?
What is the benefit of RSTP over STP in terms of network availability?
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What is the primary action of Spanning Tree Protocol when it identifies redundant connections in a LAN?
What is the primary action of Spanning Tree Protocol when it identifies redundant connections in a LAN?
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What happens to the links in a LAN when Spanning Tree Protocol is enabled?
What happens to the links in a LAN when Spanning Tree Protocol is enabled?
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What is the main reason why Spanning Tree Protocol is necessary in a network with redundant paths?
What is the main reason why Spanning Tree Protocol is necessary in a network with redundant paths?
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What is the purpose of the algorithm in Spanning Tree Protocol?
What is the purpose of the algorithm in Spanning Tree Protocol?
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What is the result of Spanning Tree Protocol selecting the best path in a network?
What is the result of Spanning Tree Protocol selecting the best path in a network?
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Why is Spanning Tree Protocol used in a LAN?
Why is Spanning Tree Protocol used in a LAN?
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What is the primary function of bridges in a network with redundant paths?
What is the primary function of bridges in a network with redundant paths?
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What is a characteristic of Spanning Tree Protocol?
What is a characteristic of Spanning Tree Protocol?
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What is a key advantage of PVSTP compared to other spanning tree protocols?
What is a key advantage of PVSTP compared to other spanning tree protocols?
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What happens when a version 0 BPDU is seen in PVRSTP?
What happens when a version 0 BPDU is seen in PVRSTP?
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In RSTP, what is the advantage of allowing Alternate and Backup ports to directly enter the forwarding state?
In RSTP, what is the advantage of allowing Alternate and Backup ports to directly enter the forwarding state?
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What is a characteristic of PVRSTP?
What is a characteristic of PVRSTP?
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What is the primary function of MSTP in a network?
What is the primary function of MSTP in a network?
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What is the primary advantage of MSTP over STP?
What is the primary advantage of MSTP over STP?
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What is the primary function of Spanning Tree Protocol in a network with redundant links?
What is the primary function of Spanning Tree Protocol in a network with redundant links?
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What is the purpose of the Listening state in STP?
What is the purpose of the Listening state in STP?
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What is the benefit of RSTP compared to STP?
What is the benefit of RSTP compared to STP?
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What is the effect of MSTP on network topology?
What is the effect of MSTP on network topology?
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What is the advantage of MSTP over other spanning tree protocols?
What is the advantage of MSTP over other spanning tree protocols?
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Which Spanning Tree Protocol is compatible with IEEE 802.1D?
Which Spanning Tree Protocol is compatible with IEEE 802.1D?
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What is the standard that defines MSTP?
What is the standard that defines MSTP?
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What is the purpose of BPDUs in spanning tree protocols?
What is the purpose of BPDUs in spanning tree protocols?
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What is the difference between RSTP and STP?
What is the difference between RSTP and STP?
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What is the purpose of BPDUs in STP?
What is the purpose of BPDUs in STP?
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What is the purpose of the root bridge in RSTP?
What is the purpose of the root bridge in RSTP?
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What determines the port cost in RSTP?
What determines the port cost in RSTP?
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What happens to a port that has been disabled and then re-enabled in STP?
What happens to a port that has been disabled and then re-enabled in STP?
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Why does STP balance states across ports?
Why does STP balance states across ports?
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What is the purpose of Bridge Protocol Data Units (BPDUs) in a network?
What is the purpose of Bridge Protocol Data Units (BPDUs) in a network?
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What happens to a port when it is in the Disabled state?
What happens to a port when it is in the Disabled state?
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What is the main benefit of RSTP over STP?
What is the main benefit of RSTP over STP?
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What is the purpose of the Listening state in STP?
What is the purpose of the Listening state in STP?
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What is the typical time frame for STP to move from one state to another?
What is the typical time frame for STP to move from one state to another?
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What happens to a port when it moves from the Listening state to the Learning state?
What happens to a port when it moves from the Listening state to the Learning state?
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What is the purpose of RSTP in a network?
What is the purpose of RSTP in a network?
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What is the purpose of the Forwarding state in STP?
What is the purpose of the Forwarding state in STP?
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What is the role of the root port in RSTP?
What is the role of the root port in RSTP?
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What happens to the address table in the Forwarding state?
What happens to the address table in the Forwarding state?
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What is the purpose of the Blocking state in STP?
What is the purpose of the Blocking state in STP?
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What happens to a port when it is in the Blocking state?
What happens to a port when it is in the Blocking state?
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What is the primary criterion for selecting the root port in a switch?
What is the primary criterion for selecting the root port in a switch?
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What is the purpose of a designated port in a LAN segment?
What is the purpose of a designated port in a LAN segment?
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What is the role of the alternate port in RSTP?
What is the role of the alternate port in RSTP?
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What is the relationship between link speed and port cost in RSTP?
What is the relationship between link speed and port cost in RSTP?
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What is the state of a port that is not forwarding traffic and not updating MAC address tables?
What is the state of a port that is not forwarding traffic and not updating MAC address tables?
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What is the purpose of Bridge Protocol Data Units (BPDUs) in RSTP?
What is the purpose of Bridge Protocol Data Units (BPDUs) in RSTP?
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What is the number of root ports per non-root switch in RSTP?
What is the number of root ports per non-root switch in RSTP?
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What happens to an alternate port when the root port fails?
What happens to an alternate port when the root port fails?
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What is the major advantage of RSTP over STP?
What is the major advantage of RSTP over STP?
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In MSTP, what is the purpose of grouping VLANs into a spanning-tree instance?
In MSTP, what is the purpose of grouping VLANs into a spanning-tree instance?
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What is the initial state of every port in RSTP?
What is the initial state of every port in RSTP?
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What is the main function of MSTP in a network?
What is the main function of MSTP in a network?
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What is the purpose of the Listening state in RSTP?
What is the purpose of the Listening state in RSTP?
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What is a benefit of using MSTP over STP?
What is a benefit of using MSTP over STP?
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What is the purpose of the root port in RSTP?
What is the purpose of the root port in RSTP?
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What is standardized by the IEEE within the 802.1Q-2014 report?
What is standardized by the IEEE within the 802.1Q-2014 report?
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What is the primary purpose of Spanning Tree Protocol in a LAN?
What is the primary purpose of Spanning Tree Protocol in a LAN?
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What happens to redundant links in a LAN when STP is enabled?
What happens to redundant links in a LAN when STP is enabled?
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What is the main advantage of Spanning Tree Protocol?
What is the main advantage of Spanning Tree Protocol?
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What is the purpose of the algorithm in Spanning Tree Protocol?
What is the purpose of the algorithm in Spanning Tree Protocol?
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Why is Spanning Tree Protocol necessary in a network with redundant paths?
Why is Spanning Tree Protocol necessary in a network with redundant paths?
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What organization standardized Spanning Tree Protocol?
What organization standardized Spanning Tree Protocol?
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What is the primary function of bridges in a network with redundant paths?
What is the primary function of bridges in a network with redundant paths?
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What is a characteristic of Spanning Tree Protocol?
What is a characteristic of Spanning Tree Protocol?
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Study Notes
Spanning Tree Protocols
- Spanning tree protocols prevent loops in a switched network with redundant paths.
- The original spanning tree protocol and algorithm were invented by Radia Perlman in 1985.
- Spanning tree protocols were later standardized by the IEEE as IEEE 802.1D.
STP (Spanning Tree Protocol)
- STP monitors all network links, identifies redundant connections, and disables ports that can lead to looping.
- Spanning trees use an algorithm to search for redundant links in the LAN and select the best paths.
- When the best path is selected, all links without a redundant link are in the forwarding state.
- The redundant links that were not as good as the selected links are in the blocking state.
- STP never uses multiple links to the same destination, so there is no load-sharing feature.
- STP balances the states across ports to avoid bridge looping while making redundancy possible.
RSTP (Rapid Spanning Tree Protocol)
- RSTP is an improvement over STP, providing high availability of network and loop-free topology within Ethernet networks.
- RSTP prevents network loops when using multiple switches by blocking redundant paths on a network.
- RSTP algorithm follows these steps:
- Determine the root bridge.
- All interfaces on the root bridge are placed in a Forwarding state.
- All other switches on the network (non-root) select a root port.
- Designated ports are selected.
- All other ports are in a discarding (blocking) state.
- RSTP port roles:
- Root Port: receives BPDUs on the root bridge.
- Designated Port: provides the lowest root path cost.
- Alternate Port: a backup for the root port in case of failure.
- Backup Port: a backup for the designated port.
RSTP States
- RSTP has three port states: Discarding, Learning, and Forwarding.
- The Disabled, Blocking, and Listening states described by STP have been combined into the Discarding state in RSTP.
- In RSTP, the Alternate port and Backup port are allowed to directly enter the forwarding state, reducing convergence time.
MSTP (Multiple Spanning Tree Protocol)
- MSTP creates multiple spanning trees (instances) for each VLAN on a single physical network.
- MSTP protocol enables VLANs to be grouped into a spanning-tree instance, provides multiple forwarding paths for data traffic, and enables load balancing.
- MSTP gives better scaling as bridges have less computations to perform.
PVSTP (Per-VLAN Spanning Tree)
- PVSTP is a CISCO proprietary version of STP.
- PVSTP maintains a spanning tree instance for each VLAN configured in the network.
- PVSTP uses ISL Trunking and allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs.
PVRSTP (Per-VLAN Rapid Spanning Tree Protocol)
- PVRSTP is based on the IEEE 8012.1w standard.
- PVRSTP supports fast convergence IEEE 802.1D.
- PVRSTP is compatible with IEEE 802.1D spanning tree.
- PVRSTP sends BPDUs on all ports, instead of only the root bridge sending BPDUs, and supports the discarding, learning, and forwarding states.
Spanning Tree Protocols
- Spanning tree protocols prevent loops in a switched network with redundant paths.
- The original spanning tree protocol and algorithm were invented by Radia Perlman in 1985.
- Spanning tree protocols were later standardized by the IEEE as IEEE 802.1D.
STP (Spanning Tree Protocol)
- STP monitors all network links, identifies redundant connections, and disables ports that can lead to looping.
- Spanning trees use an algorithm to search for redundant links in the LAN and select the best paths.
- When the best path is selected, all links without a redundant link are in the forwarding state.
- The redundant links that were not as good as the selected links are in the blocking state.
- STP never uses multiple links to the same destination, so there is no load-sharing feature.
- STP balances the states across ports to avoid bridge looping while making redundancy possible.
RSTP (Rapid Spanning Tree Protocol)
- RSTP is an improvement over STP, providing high availability of network and loop-free topology within Ethernet networks.
- RSTP prevents network loops when using multiple switches by blocking redundant paths on a network.
- RSTP algorithm follows these steps:
- Determine the root bridge.
- All interfaces on the root bridge are placed in a Forwarding state.
- All other switches on the network (non-root) select a root port.
- Designated ports are selected.
- All other ports are in a discarding (blocking) state.
- RSTP port roles:
- Root Port: receives BPDUs on the root bridge.
- Designated Port: provides the lowest root path cost.
- Alternate Port: a backup for the root port in case of failure.
- Backup Port: a backup for the designated port.
RSTP States
- RSTP has three port states: Discarding, Learning, and Forwarding.
- The Disabled, Blocking, and Listening states described by STP have been combined into the Discarding state in RSTP.
- In RSTP, the Alternate port and Backup port are allowed to directly enter the forwarding state, reducing convergence time.
MSTP (Multiple Spanning Tree Protocol)
- MSTP creates multiple spanning trees (instances) for each VLAN on a single physical network.
- MSTP protocol enables VLANs to be grouped into a spanning-tree instance, provides multiple forwarding paths for data traffic, and enables load balancing.
- MSTP gives better scaling as bridges have less computations to perform.
PVSTP (Per-VLAN Spanning Tree)
- PVSTP is a CISCO proprietary version of STP.
- PVSTP maintains a spanning tree instance for each VLAN configured in the network.
- PVSTP uses ISL Trunking and allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs.
PVRSTP (Per-VLAN Rapid Spanning Tree Protocol)
- PVRSTP is based on the IEEE 8012.1w standard.
- PVRSTP supports fast convergence IEEE 802.1D.
- PVRSTP is compatible with IEEE 802.1D spanning tree.
- PVRSTP sends BPDUs on all ports, instead of only the root bridge sending BPDUs, and supports the discarding, learning, and forwarding states.
Spanning Tree Protocols
- Spanning tree protocols prevent loops in a switched network with redundant links by monitoring all network links, identifying redundant connections, and disabling ports that can lead to looping.
- The original spanning tree protocol was invented by Radia Perlman in 1985 and later standardized by the IEEE as IEEE 802.1D.
STP Port States
- Disabled: ports are totally disabled and do not participate in frame forwarding or STP operations.
- Blocking: ports discard frames received from the attached network segment, but continue to listen for and process BPDUs.
- Listening: ports discard frames from the attached network segment or forwarded from another port, but receive BPDUs and redirect them to the switch module for processing.
- Learning: ports listen for and process BPDUs, discard frames from the attached network segment or forwarded from another port, and update the address table with learned information.
- Forwarding: ports forward frames across network segments, continue to receive and process BPDUs, and update the address table.
RSTP (Rapid Spanning Tree Protocol)
- RSTP is an improvement over STP that provides high availability of network and loop-free topology within Ethernet networks.
- RSTP prevents network loops by blocking redundant paths on a network and establishes a root bridge.
- The RSTP algorithm determines the root bridge, places all interfaces on the root bridge in a forwarding state, and selects a root port on non-root bridges based on port cost.
MSTP (Multiple Spanning Tree Protocol)
- MSTP creates multiple spanning trees (instances) for each Virtual LAN (VLAN) on a single physical network.
- MSTP uses RSTP to provide rapid convergence and enables VLANs to be grouped into a spanning-tree instance.
- MSTP provides for multiple forwarding paths for data traffic and enables load balancing.
PVSTP (Per-VLAN Spanning Tree Protocol)
- PVSTP is a CISCO proprietary version of STP that maintains a spanning tree instance for each VLAN configured in the network.
- PVSTP uses ISL Trunking and allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs.
- PVSTP has the ability to load balance traffic by forwarding some VLANs on one trunk and other VLANs on another trunk without causing a Spanning Tree loop.
PVRSTP (Per-VLAN Rapid Spanning Tree Protocol)
- PVRSTP is based on the IEEE 8012.1w standard and supports fast convergence.
- PVRSTP sends BPDUs on all ports, instead of only the root bridge sending BPDUs, and supports the discarding, learning, and forwarding states.
- PVRSTP embeds support for PVSTP FastBackbone and FastUplink.
Spanning Tree Protocols
- Spanning tree protocols are used to monitor and control network links, identify redundant connections, and disable ports that can lead to looping.
- The original spanning tree protocol was invented by Radia Perlman in 1985 and later standardized by the IEEE as IEEE 802.1D.
Spanning Tree Operation
- Spanning tree algorithms search for redundant links in the LAN and select the best paths.
- All links without a redundant link are in the forwarding state, while redundant links are in the blocking state.
- Spanning tree protocols do not use multiple links to the same destination, i.e., there is no load-sharing feature.
STP Port States
- Disabled: ports are totally disabled and do not participate in frame forwarding or STP operations.
- Blocking: ports do not participate in frame forwarding and discard frames received from the attached network segment, but continue to listen for and process BPDUs.
- Listening: ports discard frames from the attached network segment or forwarded from another port, but receive BPDUs and redirect them to the switch module for processing.
- Learning: ports listen for and process BPDUs, but discard frames from the attached network segment or forwarded from another port, and start updating the address table with learned information.
- Forwarding: ports move from the learning state to the forwarding state and start forwarding frames across network segments, continue to receive and process BPDUs, and update the address table.
Rapid Spanning Tree Protocol (RSTP)
- RSTP is an improvement over STP, providing high availability of network and loop-free topology within Ethernet networks.
- RSTP prevents network loops when using multiple switches by blocking redundant paths on a network.
- RSTP algorithm steps:
- Determine the root bridge: the switch with the lowest bridge priority will be the root bridge.
- All interfaces on the root bridge are placed in a Forwarding state.
- All other switches on the network (non-root) select a root port: the best path to the root bridge based on its port cost.
- Designated ports are selected: these ports are permitted to forward traffic and are also selected based on port cost.
- All other ports are in a discarding (blocking) state.
RSTP Port Roles
- Root Port: the port that receives Bridge Protocol Data Units (BPDUs) on the root bridge.
- Designated Port: the port selected in each local area network (LAN) segment that provides the lowest root path cost.
- Alternate Port: a backup for the root port in case of failure, blocked during typical operation of the root port.
- Backup Port: a backup for the designated port, blocked during typical operation of the designated port.
RSTP States
- Discarding: combines the Disabled, Blocking, and Listening states of STP, where the port only listens for BPDUs and does not forward, process, or learn MAC addresses.
- Learning: the port sends and receives BPDUs and also learns MAC addresses, but does not forward data.
- Forwarding: the port can send and receive data, learn MAC addresses, and forward data to its destination.
Multiple Spanning Tree Protocol (MSTP)
- MSTP creates multiple spanning trees (instances) for each Virtual LAN (VLAN) on a single physical network.
- MSTP allows for each VLAN to have a configured root bridge and forwarding topology.
- MSTP enables load balancing and provides better scaling as bridges have less computations to perform.
- MSTP is standardized by the IEEE within the 802.1Q-2014 report.
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Description
Learn about spanning tree protocols, their purpose, and how they work in switched networks with redundant paths. Discover the original protocol and its standardization by IEEE.