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Questions and Answers

What is the primary goal of Spanning Tree Protocol (STP) in a switched network?

To prevent network congestion

To increase network security

To enable load sharing across multiple links

To prevent loop creation in the network (correct)

Who invented the original Spanning Tree Protocol and algorithm?

IEEE

Digital Equipment Corporation

Radia Perlman (correct)

John Smith

What is the purpose of Spanning Tree Protocol in a network with redundant paths?

To improve network latency

To enable load balancing

To control the flow of traffic and prevent looping (correct)

To increase network bandwidth

What is the result of Spanning Tree Protocol selecting the best path in a network?

Links without redundant links are in forwarding state Signup and view all the answers

What is the standard for Spanning Tree Protocol set by?

IEEE 802.1D Signup and view all the answers

What is the main function of Spanning Tree Protocol in a LAN?

To identify redundant connections Signup and view all the answers

Why do bridges need to continually understand the topology of the network?

To control the flow of traffic and prevent looping Signup and view all the answers

What is a characteristic of Spanning Tree Protocol?

It does not use multiple links to the same destination Signup and view all the answers

What is the typical time frame for STP to move from one state to another?

15-20 seconds Signup and view all the answers

What is the initial state of every port in STP?

Blocking state Signup and view all the answers

What is the primary advantage of RSTP networks?

High availability Signup and view all the answers

How does RSTP prevent network loops?

By blocking redundant paths Signup and view all the answers

What is the first step in the RSTP algorithm?

Determine the root bridge Signup and view all the answers

How is the root bridge selected in RSTP?

By the switch with the lowest bridge priority and MAC address Signup and view all the answers

What is the purpose of the root port in RSTP?

To determine the best path to the root bridge Signup and view all the answers

What determines the port cost in RSTP?

Port speed Signup and view all the answers

What is an advantage of RSTP over STP?

Faster convergence time Signup and view all the answers

In STP, what happens to the port before entering the forwarding state?

It waits for the network to converge Signup and view all the answers

What is the purpose of MSTP?

To enable load balancing and rapid convergence Signup and view all the answers

What is a characteristic of the Listening state in STP?

The port sends and receives BPDUs and learns MAC addresses Signup and view all the answers

What is the result of MSTP enabling VLANs to share STP instances?

Better scaling as bridges have less computations to perform Signup and view all the answers

What is standardized by the IEEE within the 802.1Q-2014 report?

MSTP Signup and view all the answers

What is the Discarding state in STP?

The port does not forward, process, or learn MAC addresses Signup and view all the answers

What is a benefit of RSTP over STP?

Rapid convergence of the spanning tree Signup and view all the answers

What is a distinct feature of PVSTP?

It is based on the IEEE 8012.1w standard Signup and view all the answers

What is the primary advantage of RSTP compared to STP?

Faster convergence time Signup and view all the answers

What happens when a version 0 BPDU is seen in PVRSTP?

PVRSTP reverts to sending version 0 BPDUs Signup and view all the answers

What is the function of MSTP in a network?

To create multiple spanning tree instances for each VLAN Signup and view all the answers

What is the effect of load balancing in PVSTP?

Traffic is forwarded on multiple trunks for different VLANs Signup and view all the answers

What is the standard supported by PVRSTP?

IEEE 8012.1w Signup and view all the answers

What is the difference between PVSTP and PVRSTP?

PVRSTP is based on IEEE 8012.1w, while PVSTP is Cisco proprietary Signup and view all the answers

What is a common feature of both PVSTP and PVRSTP?

Load balancing of traffic Signup and view all the answers

What is the criteria for selecting the root port in a switch?

Lowest port cost Signup and view all the answers

What is the purpose of a designated port in a LAN segment?

To provide the lowest root path cost Signup and view all the answers

What happens to an alternate port when the root port fails?

It becomes the new designated port Signup and view all the answers

What is the purpose of a backup port in RSTP?

To act as a backup for the designated port Signup and view all the answers

What is the number of root ports per non-root switch in RSTP?

One Signup and view all the answers

What are Bridge Protocol Data Units (BPDUs) used for?

To exchange messages between switches Signup and view all the answers

What is the state of a port that is not forwarding traffic and not updating MAC address tables?

Discarding Signup and view all the answers

What is the relationship between link speed and port cost in RSTP?

Higher link speed, lower port cost Signup and view all the answers

What happens to redundant links in a LAN when STP is enabled?

They are blocked to prevent looping Signup and view all the answers

What is the purpose of an algorithm in Spanning Tree Protocol?

To search for the redundant links in the LAN Signup and view all the answers

What is a characteristic of Spanning Tree Protocol?

It puts all links in either forwarding or blocking state Signup and view all the answers

Why is Spanning Tree Protocol necessary in a network with redundant paths?

To prevent looping and control the flow of traffic Signup and view all the answers

What organization standardized Spanning Tree Protocol?

Institute of Electrical and Electronics Engineers (IEEE) Signup and view all the answers

What is the primary function of bridges in a network with redundant paths?

To control the flow of traffic and prevent looping Signup and view all the answers

What is a feature of Spanning Tree Protocol?

It does not use multiple links to the same destination Signup and view all the answers

What is the purpose of Spanning Tree Protocol in a local area network?

To prevent looping and control the flow of traffic Signup and view all the answers

What is the main reason for STP to balance states across ports?

To avoid bridge looping Signup and view all the answers

What is the role of the root bridge in RSTP?

To send and receive data and learn MAC addresses on the network Signup and view all the answers

What happens to a port that has been disabled in STP?

It enters the blocking state Signup and view all the answers

What is the purpose of RSTP in Ethernet networks?

To provide high availability of network and loop-free topology Signup and view all the answers

How is the root port selected in RSTP?

Based on the lowest port cost Signup and view all the answers

What is the advantage of RSTP over traditional network architectures?

It minimizes downtime Signup and view all the answers

What is the purpose of blocking redundant paths in RSTP?

To prevent network loops Signup and view all the answers

What determines the port cost in RSTP?

The link speed Signup and view all the answers

What is the primary advantage of RSTP over STP in terms of convergence time?

RSTP has a significantly faster convergence time than STP. Signup and view all the answers

What is the purpose of the Listening state in STP?

The port only listens for BPDUs and does not forward traffic. Signup and view all the answers

What does MSTP enable for each VLAN?

A separate spanning tree instance for each VLAN. Signup and view all the answers

What is the benefit of MSTP in terms of scalability?

MSTP reduces the computational load on bridges. Signup and view all the answers

What is the state of a port that is learning MAC addresses but not forwarding traffic?

Learning Signup and view all the answers

What is the primary advantage of MSTP over STP?

MSTP enables more scalable and flexible network topologies. Signup and view all the answers

What is the purpose of MSTP in a network?

To enable load balancing and multiple forwarding paths for data traffic. Signup and view all the answers

What is the standardized protocol that MSTP is based on?

IEEE 802.1Q-2014 Signup and view all the answers

What is the main advantage of PVSTP in a switched network?

It allows load balancing traffic at layer-2 Signup and view all the answers

What happens when a version 0 BPDU is seen in PVRSTP?

It reverts to sending version 0 BPDUs Signup and view all the answers

What is the primary function of PVRSTP in a network?

It embeds support for PVSTP FastBackbone and FastUplink Signup and view all the answers

What is the main difference between PVSTP and PVRSTP?

PVSTP is a CISCO proprietary version, while PVRSTP is based on the IEEE 8012.1w standard Signup and view all the answers

What is the advantage of MSTP over STP?

It enables VLANs to share STP instances Signup and view all the answers

What is the purpose of Spanning Tree Protocol in a network with redundant paths?

To prevent network loops Signup and view all the answers

What is the standard supported by PVRSTP?

IEEE 8012.1w Signup and view all the answers

What is the primary advantage of RSTP over STP?

It reduces the convergence time of the network Signup and view all the answers

What is the primary criterion for selecting the root port in a switch?

Lowest port cost Signup and view all the answers

What happens to an alternate port when the root port fails?

It becomes the new root port Signup and view all the answers

What is the purpose of a backup port in RSTP?

To act as a backup for the designated port Signup and view all the answers

What is the state of a port that is not forwarding traffic and not updating MAC address tables?

Discarding Signup and view all the answers

How many root ports are there per non-root switch in RSTP?

One Signup and view all the answers

What is the purpose of a designated port in a LAN segment?

To provide the lowest root path cost Signup and view all the answers

What are Bridge Protocol Data Units (BPDUs) used for?

To exchange messages between switches Signup and view all the answers

What determines the port cost in RSTP?

Link speed Signup and view all the answers

What is the purpose of Bridge Protocol Data Units (BPDUs) in a spanning tree protocol?

To provide bridges with network information used to carry out STP operations Signup and view all the answers

What is the primary function of a port in the Listening state in STP?

To receive and process BPDUs Signup and view all the answers

What happens to a port when it transitions from the Listening state to the Learning state in STP?

It starts updating the address table with learned information Signup and view all the answers

What is the state of a port that has been disabled and then enabled in STP?

Blocking Signup and view all the answers

What is the main reason for STP to balance states across ports?

To prevent bridge looping Signup and view all the answers

What is the purpose of the Disabled state in STP?

To totally disable the port, preventing frame forwarding and STP operations Signup and view all the answers

What is the primary function of a port in the Forwarding state in STP?

To forward frames across network segments Signup and view all the answers

How does RSTP ensure a loop-free topology in Ethernet networks?

By blocking redundant paths Signup and view all the answers

What determines the root bridge in RSTP?

The switch with the lowest bridge priority Signup and view all the answers

What happens to a port in the Blocking state in STP?

It discards frames from the attached network segment Signup and view all the answers

What is the primary function of a port in the Learning state in STP?

To update the address table with learned information Signup and view all the answers

What is the purpose of the root port in RSTP?

To find the best path to the root bridge Signup and view all the answers

What happens to the address table in the Forwarding state in STP?

It continues to be updated Signup and view all the answers

What is the relationship between link speed and port cost in RSTP?

The lower the link speed, the higher the port cost Signup and view all the answers

What happens to all interfaces on the root bridge in RSTP?

They are placed in a Forwarding state Signup and view all the answers

What is the benefit of RSTP over STP in terms of network availability?

RSTP has higher network availability Signup and view all the answers

What is the primary action of Spanning Tree Protocol when it identifies redundant connections in a LAN?

Disables the ports that can lead to looping Signup and view all the answers

What happens to the links in a LAN when Spanning Tree Protocol is enabled?

The best path is selected and the links are either in the forwarding or blocking state Signup and view all the answers

What is the main reason why Spanning Tree Protocol is necessary in a network with redundant paths?

To prevent network loops Signup and view all the answers

What is the purpose of the algorithm in Spanning Tree Protocol?

To identify redundant links Signup and view all the answers

What is the result of Spanning Tree Protocol selecting the best path in a network?

The selected links are in the forwarding state and the others are in the blocking state Signup and view all the answers

Why is Spanning Tree Protocol used in a LAN?

To prevent network loops and control the flow of traffic Signup and view all the answers

What is the primary function of bridges in a network with redundant paths?

To control the flow of traffic and prevent looping Signup and view all the answers

What is a characteristic of Spanning Tree Protocol?

It is mainly used to put all links in either forwarding or blocking state Signup and view all the answers

What is a key advantage of PVSTP compared to other spanning tree protocols?

Load balancing at layer-2 Signup and view all the answers

What happens when a version 0 BPDU is seen in PVRSTP?

PVRSTP reverts to sending version 0 BPDUs Signup and view all the answers

In RSTP, what is the advantage of allowing Alternate and Backup ports to directly enter the forwarding state?

Reduced network convergence time Signup and view all the answers

What is a characteristic of PVRSTP?

It sends BPDUs on all ports Signup and view all the answers

What is the primary function of MSTP in a network?

Enabling VLANs to be grouped into a single spanning-tree instance Signup and view all the answers

What is the primary advantage of MSTP over STP?

Improved network scalability Signup and view all the answers

What is the primary function of Spanning Tree Protocol in a network with redundant links?

To prevent network loops Signup and view all the answers

What is the purpose of the Listening state in STP?

Sending and receiving BPDUs Signup and view all the answers

What is the benefit of RSTP compared to STP?

Faster convergence time Signup and view all the answers

What is the effect of MSTP on network topology?

It creates multiple spanning trees for each VLAN Signup and view all the answers

What is the advantage of MSTP over other spanning tree protocols?

Creates multiple spanning trees for each VLAN Signup and view all the answers

Which Spanning Tree Protocol is compatible with IEEE 802.1D?

PVRSTP Signup and view all the answers

What is the standard that defines MSTP?

IEEE 802.1Q-2014 Signup and view all the answers

What is the purpose of BPDUs in spanning tree protocols?

To send configuration information Signup and view all the answers

What is the difference between RSTP and STP?

RSTP has faster convergence, while STP has slower convergence Signup and view all the answers

What is the purpose of BPDUs in STP?

To send and receive configuration messages Signup and view all the answers

What is the purpose of the root bridge in RSTP?

To determine the most efficient way to send broadcasts across the network Signup and view all the answers

What determines the port cost in RSTP?

The port speed, with lower speeds having a higher cost Signup and view all the answers

What happens to a port that has been disabled and then re-enabled in STP?

It enters the blocking state immediately Signup and view all the answers

Why does STP balance states across ports?

To prevent bridge looping Signup and view all the answers

What is the purpose of Bridge Protocol Data Units (BPDUs) in a network?

To provide bridges with network information for STP operations Signup and view all the answers

What happens to a port when it is in the Disabled state?

It is totally disabled and does not participate in frame forwarding or STP operations Signup and view all the answers

What is the main benefit of RSTP over STP?

RSTP offers faster convergence than STP Signup and view all the answers

What is the purpose of the Listening state in STP?

To receive and process BPDUs but discard user frames Signup and view all the answers

What is the typical time frame for STP to move from one state to another?

Between 15 to 20 seconds Signup and view all the answers

What happens to a port when it moves from the Listening state to the Learning state?

It starts updating the address table with learned information Signup and view all the answers

What is the purpose of RSTP in a network?

To provide high availability of network and loop-free topology Signup and view all the answers

What is the purpose of the Forwarding state in STP?

To forward frames across network segments and continue updating the address table Signup and view all the answers

What is the role of the root port in RSTP?

To provide the best path to the root bridge Signup and view all the answers

What happens to the address table in the Forwarding state?

It is updated with learned information Signup and view all the answers

What is the purpose of the Blocking state in STP?

To receive and process BPDUs but discard user frames Signup and view all the answers

What happens to a port when it is in the Blocking state?

It discards frames and continues to listen for and process BPDUs Signup and view all the answers

What is the primary criterion for selecting the root port in a switch?

Port with the lowest port cost Signup and view all the answers

What is the purpose of a designated port in a LAN segment?

To forward traffic and provide the lowest root path cost Signup and view all the answers

What is the role of the alternate port in RSTP?

To provide a backup for the designated port Signup and view all the answers

What is the relationship between link speed and port cost in RSTP?

Higher link speed results in lower port cost Signup and view all the answers

What is the state of a port that is not forwarding traffic and not updating MAC address tables?

Discarding state Signup and view all the answers

What is the purpose of Bridge Protocol Data Units (BPDUs) in RSTP?

To exchange messages between switches on the network Signup and view all the answers

What is the number of root ports per non-root switch in RSTP?

One Signup and view all the answers

What happens to an alternate port when the root port fails?

It becomes the new root port Signup and view all the answers

What is the major advantage of RSTP over STP?

RSTP allows for faster convergence of the network Signup and view all the answers

In MSTP, what is the purpose of grouping VLANs into a spanning-tree instance?

To reduce the number of computations for bridges Signup and view all the answers

What is the initial state of every port in RSTP?

Discarding Signup and view all the answers

What is the main function of MSTP in a network?

To create multiple spanning trees for each VLAN Signup and view all the answers

What is the purpose of the Listening state in RSTP?

To send and receive BPDUs Signup and view all the answers

What is a benefit of using MSTP over STP?

Load balancing for VLANs Signup and view all the answers

What is the purpose of the root port in RSTP?

To forward data to its destination Signup and view all the answers

What is standardized by the IEEE within the 802.1Q-2014 report?

MSTP Signup and view all the answers

What is the primary purpose of Spanning Tree Protocol in a LAN?

To prevent network loops and improve performance Signup and view all the answers

What happens to redundant links in a LAN when STP is enabled?

They are disabled to prevent network loops Signup and view all the answers

What is the main advantage of Spanning Tree Protocol?

It prevents network loops and improves performance Signup and view all the answers

What is the purpose of the algorithm in Spanning Tree Protocol?

To search for redundant links and select the best paths Signup and view all the answers

Why is Spanning Tree Protocol necessary in a network with redundant paths?

To prevent network loops and improve performance Signup and view all the answers

What organization standardized Spanning Tree Protocol?

IEEE Signup and view all the answers

What is the primary function of bridges in a network with redundant paths?

To continually understand the topology of the network Signup and view all the answers

What is a characteristic of Spanning Tree Protocol?

It prevents network loops and improves performance Signup and view all the answers

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.