Layer 2 Switching Configuration Guide, Cisco DCNM for LAN, Release 5.x
Configuring Rapid PVST+
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Configuring Rapid PVST+

Contents

Configuring Rapid PVST+

This chapter describes how to configure the Rapid per VLAN Spanning Tree (Rapid PVST+) protocol on Cisco NX-OS devices using Cisco Data Center Manager (DCNM) for LAN.

For more information about the Cisco DCNM features, see the .

This chapter includes the following sections:

Information About Rapid PVST+


Note


See the Interfaces Configuration Guide, Cisco DCNM for LAN, Release 5.x, for information on creating Layer 2 interfaces.


The Spanning Tree Protocol (STP) was implemented to provide a loop-free network at Layer 2 of the network. Rapid PVST+ is an updated implementation of STP that allows you to create one spanning tree topology for each VLAN. Rapid PVST+ is the default STP mode on the device.


Note


Spanning tree is used to refer to IEEE 802.1w and IEEE 802.1s. If the IEEE 802.1D Spanning Tree Protocol is discussed in this publication, then 802.1D is stated specifically.


The Rapid PVST+ protocol is the IEEE 802.1w standard, Rapid Spanning Tree Protocol (RSTP), implemented on a per VLAN basis. Rapid PVST+ interoperates with the IEEE 802.1Q VLAN standard, which mandates a single STP instance for all VLANs, rather than per VLAN.

Rapid PVST+ is enabled by default on the default VLAN (VLAN1) and on all newly created VLANs on the device. Rapid PVST+ interoperates with devices that run legacy IEEE 802.1D STP.

RSTP is an improvement on the original STP standard, 802.1D, which allows faster convergence.


Note


The device supports full nondisruptive upgrades for Rapid PVST+. See the Cisco Nexus 7000 Series NX-OS High Availability and Redundancy Guide, Release 5.x, for complete information on nondisruptive upgrades.


The Cisco NX-OS release that is running on a managed device many not support all the features or settings described in this chapter. For the latest feature information and caveats, see the documentation and release notes for your platform and software release.

STP

STP is a Layer 2 link-management protocol that provides path redundancy while preventing loops in the network.

Overview of STP

In order for a Layer 2 Ethernet network to function properly, only one active path can exist between any two stations. STP operation is transparent to end stations, which cannot detect whether they are connected to a single LAN segment or a switched LAN of multiple segments.

When you create fault-tolerant internetworks, you must have a loop-free path between all nodes in a network. The STP algorithm calculates the best loop-free path throughout a switched Layer 2 network. Layer 2 LAN ports send and receive STP frames, which are called Bridge Protocol Data Units (BPDUs), at regular intervals. Network devices do not forward these frames but use the frames to construct a loop-free path.

Multiple active paths between end stations cause loops in the network. If a loop exists in the network, end stations might receive duplicate messages and network devices might learn end station MAC addresses on multiple Layer 2 LAN ports.

STP defines a tree with a root bridge and a loop-free path from the root to all network devices in the Layer 2 network. STP forces redundant data paths into a blocked state. If a network segment in the spanning tree fails and a redundant path exists, the STP algorithm recalculates the spanning tree topology and activates the blocked path.

When two Layer 2 LAN ports on a network device are part of a loop, the STP port priority and port path-cost setting determine which port on the device is put in the forwarding state and which port is put in the blocking state. The STP port priority value is the efficiency with which that location allows the port to pass traffic. The STP port path-cost value is derived from the media speed.

How a Topology is Created

All devices in a LAN that participate in a spanning tree gather information about other switches in the network by exchanging BPDUs. This exchange of BPDUs results in the following actions:


  • The system elects a unique root switch for the spanning tree network topology.

  • The system elects a designated switch for each LAN segment.

  • The system eliminates any loops in the switched network by placing redundant switch ports in a backup state; all paths that are not needed to reach the root device from anywhere in the switched network are placed in an STP-blocked state.

The topology on an active switched network is determined by the following:


  • The unique device identifier Media Access Control (MAC) address of the device that is associated with each device

  • The path cost to the root that is associated with each switch port

  • The port identifier that is associated with each switch port

In a switched network, the root switch is the logical center of the spanning tree topology. STP uses BPDUs to elect the root switch and root port for the switched network.

Bridge ID

Each VLAN on each network device has a unique 64-bit bridge ID that consists of a bridge priority value, an extended system ID (IEEE 802.1t), and an STP MAC address allocation.

Bridge Priority Value

The bridge priority is a 4-bit value when the extended system ID is enabled.

You can only specify a device bridge ID (used by the spanning tree algorithm to determine the identity of the root bridge; the lowest number is preferred) as a multiple of 4096.


Note


In this device, the extended system ID is always enabled; you cannot disable the extended system ID.


Extended System ID

The device always uses the 12-bit extended system ID.

This figure shows the 12-bit extended system ID field that is part of the bridge ID.
Figure 1. Bridge ID with Extended System ID

This table shows how the system ID extension combined with the bridge ID functions as the unique identifier for a VLAN.
Table 1 Bridge Priority Value and Extended System ID with the Extended System ID Enabled

Bridge Priority Value

Extended System ID (Set Equal to the VLAN ID)

Bit 16

Bit 15

Bit 14

Bit 13

Bit 12

Bit 11

Bit 10

Bit 9

Bit 8

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

32768

16384

8192

4096

2048

1024

512

256

128

64

32

16

8

4

2

1

STP MAC Address Allocation


Note


MAC address reduction is always enabled on the device.


Because MAC address reduction is always enabled on the device, you should also enable MAC address reduction on all other Layer 2 connected network devices to avoid undesirable root bridge election and spanning tree topology issues.

When MAC address reduction is enabled, the root bridge priority becomes a multiple of 4096 plus the VLAN ID. You can only specify a device bridge ID (used by the spanning tree algorithm to determine the identity of the root bridge; the lowest number is preferred) as a multiple of 4096. Only the following values are possible:


  • 0

  • 4096

  • 8192

  • 12288

  • 16384

  • 20480

  • 24576

  • 28672

  • 32768

  • 36864

  • 40960

  • 45056

  • 49152

  • 53248

  • 57344

  • 61440

STP uses the extended system ID plus a MAC address to make the bridge ID unique for each VLAN.


Note


If another bridge in the same spanning tree domain does not run the MAC address reduction feature, it could win the root bridge ownership because of the finer granularity in the selection of its bridge ID.


BPDUs

Network devices transmit BPDUs throughout the STP instance. Each network device sends configuration BPDUs to communicate and compute the spanning tree topology. Each configuration BPDU contains the following minimal information:


  • The unique bridge ID of the network device that the transmitting network device believes to be the root bridge

  • The STP path cost to the root

  • The bridge ID of the transmitting bridge

  • The message age

  • The identifier of the transmitting port

  • Values for the hello, forward delay, and max-age protocol timer

  • Additional information for STP extension protocols

When a network device transmits a Rapid PVST+ BPDU frame, all network devices connected to the VLAN on which the frame is transmitted receive the BPDU. When a network device receives a BPDU, it does not forward the frame but instead uses the information in the frame to calculate a BPDU. If the topology changes, the device initiates a BPDU exchange.

A BPDU exchange results in the following:


  • One network device is elected as the root bridge.

  • The shortest distance to the root bridge is calculated for each network device based on the path cost.

  • A designated bridge for each LAN segment is selected. This network device is closest to the root bridge through which frames are forwarded to the root.

  • A root port is elected. This port provides the best path from the bridge to the root bridge.

  • Ports included in the spanning tree are selected.

Election of the Root Bridge

For each VLAN, the network device with the highest bridge ID (that is, the lowest numerical ID value) is elected as the root bridge. If all network devices are configured with the default priority (32768), the network device with the lowest MAC address in the VLAN becomes the root bridge. The bridge priority value occupies the most significant bits of the bridge ID.

When you change the bridge priority value, you change the probability that the device will be elected as the root bridge. Configuring a lower value increases the probability; a higher value decreases the probability.

The STP root bridge is the logical center of each spanning tree topology in a Layer 2 network. All paths that are not needed to reach the root bridge from anywhere in the Layer 2 network are placed in STP blocking mode.

BPDUs contain information about the transmitting bridge and its ports, including bridge and MAC addresses, bridge priority, port priority, and path cost. STP uses this information to elect the root bridge for the STP instance, to elect the root port that leads to the root bridge, and to determine the designated port for each Layer 2 segment.

Creating the Spanning Tree Topology

By increasing the priority (lowering the numerical value) of the ideal network device so that it becomes the root bridge, you force an STP recalculation to form a new spanning tree topology with the ideal network device as the root.

In this figure, switch A is elected as the root bridge because the bridge priority of all the network devices is set to the default (32768) and switch A has the lowest MAC address. However, due to traffic patterns, the number of forwarding ports, or link types, switch A might not be the ideal root bridge.
Figure 2. Spanning Tree Topology

When the spanning tree topology is calculated based on default parameters, the path between the source and destination end stations in a switched network might not be ideal. For instance, connecting higher-speed links to a port that has a higher number than the current root port can cause a root-port change. The goal is to make the fastest link the root port.

For example, assume that one port on switch B is a fiber-optic link, and another port on switch B (an unshielded twisted-pair [UTP] link) is the root port. Network traffic might be more efficient over the high-speed fiber-optic link. By changing the STP port priority on the fiber-optic port to a higher priority (lower numerical value) than the root port, the fiber-optic port becomes the new root port.

Rapid PVST+

Rapid PVST+ is the default spanning tree mode for the software and is enabled by default on the default VLAN and all newly created VLANs.

A single instance, or topology, of RSTP runs on each configured VLAN, and each Rapid PVST+ instance on a VLAN has a single root device. You can enable and disable STP on a per-VLAN basis when you are running Rapid PVST+.

Overview of Rapid PVST+

Rapid PVST+ is the IEEE 802.1w (RSTP) standard implemented per VLAN. A single instance of STP runs on each configured VLAN (if you do not manually disable STP). Each Rapid PVST+ instance on a VLAN has a single root switch. You can enable and disable STP on a per-VLAN basis when you are running Rapid PVST+.


Note


Rapid PVST+ is the default STP mode for the device.


Rapid PVST+ uses point-to-point wiring to provide rapid convergence of the spanning tree. The spanning tree reconfiguration can occur in less than 1 second with Rapid PVST+ (in contrast to 50 seconds with the default settings in the 802.1D STP). The device automatically checks the PVID.


Note


Rapid PVST+ supports one STP instance for each VLAN.


Using Rapid PVST+, STP convergence occurs rapidly. By default, each designated port in the STP sends out a BPDU every 2 seconds. On a designated port in the topology, if hello messages are missed three consecutive times, or if the maximum age expires, the port immediately flushes all protocol information in the table. A port considers that it loses connectivity to its direct neighbor designated port if it misses three BPDUs or if the maximum age expires. This rapid aging of the protocol information allows quick failure detection.

Rapid PVST+ provides for rapid recovery of connectivity following the failure of a device, a device port, or a LAN. It provides rapid convergence for edge ports, new root ports, and ports connected through point-to-point links as follows:


  • Edge ports—When you configure a port as an edge port on an RSTP device, the edge port immediately transitions to the forwarding state. (This immediate transition was previously a Cisco-proprietary feature named PortFast.) You should only configure ports that connect to a single end station as edge ports. Edge ports do not generate topology changes when the link changes.


Note


We recommend that you configure all ports connected to a Layer 2 host as edge ports.



  • Root port—If Rapid PVST+ selects a new root port, it blocks the old root port and immediately transitions the new root port to the forwarding state.

  • Point-to-point links—If you connect a port to another port through a point-to-point link and the local port becomes a designated port, it negotiates a rapid transition with the other port by using the proposal-agreement handshake to ensure a loop-free topology.

Rapid PVST+ achieves rapid transition to the forwarding state only on edge ports and point-to-point links. Although the link type is configurable, the system automatically derives the link type information from the duplex setting of the port. Full-duplex ports are assumed to be point-to-point ports, while half-duplex ports are assumed to be shared ports.

Edge ports do not generate topology changes, but all other designated and root ports generate a topology change (TC) BPDU when they either fail to receive three consecutive BPDUs from the directly connected neighbor or the maximum age times out. At this point, the designated or root port sends a BPDU with the TC flag set. The BPDUs continue to set the TC flag as long as the TC While timer runs on that port. The value of the TC While timer is the value set for the hello time plus 1 second. The initial detector of the topology change immediately floods this information throughout the entire topology.

When Rapid PVST+ detects a topology change, the protocol does the following:


  • Starts the TC While timer with a value equal to twice the hello time for all the nonedge root and designated ports, if necessary.

  • Flushes the MAC addresses associated with all these ports.

The topology change notification floods quickly across the entire topology. The system flushes dynamic entries immediately on a per-port basis when it receives a topology change.


Note


The TCA flag is used only when the device is interacting with devices that are running legacy 802.1D STP.


The proposal and agreement sequence then quickly propagates toward the edge of the network and quickly restores connectivity after a topology change.

Rapid PVST+ BPDUs

Rapid PVST+ and 802.1w use all six bits of the flag byte to add the following:


  • The role and state of the port that originates the BPDU

  • The proposal and agreement handshake

This figure shows the use of the BPDU flags in Rapid PVST+.


Figure 3. Rapid PVST+ Flag Byte in BPDU

Another important change is that the Rapid PVST+ BPDU is type 2, version 2, which makes it possible for the device to detect connected legacy (802.1D) bridges. The BPDU for 802.1D is type 0, version 0.

Proposal and Agreement Handshake

In this figure, switch A is connected to switch B through a point-to-point link, and all of the ports are in the blocking state. Assume that the priority of switch A is a smaller numerical value than the priority of switch B. Switch A sends a proposal message (a configuration BPDU with the proposal flag set) to switch B, proposing itself as the designated switch.

After receiving the proposal message, switch B selects as its new root port the port from which the proposal message was received, forces all nonedge ports to the blocking state, and sends an agreement message (a BPDU with the agreement flag set) through its new root port.

After receiving the agreement message from switch B, switch A also immediately transitions its designated port to the forwarding state. No loops in the network can form because switch B blocked all of its nonedge ports and because there is a point-to-point link between switches A and B.

When switch C connects to switch B, a similar set of handshaking messages are exchanged. Switch C selects the port connected to switch B as its root port, and both ends of the link immediately transition to the forwarding state. With each iteration of this handshaking process, one more switch joins the active topology. As the network converges, this proposal-agreement handshaking progresses from the root toward the leaves of the spanning tree as shown in this figure.


Figure 4. Proposal and Agreement Handshaking for Rapid Convergence

The switch learns the link type from the port duplex mode; a full-duplex port is considered to have a point-to-point connection and a half-duplex port is considered to have a shared connection. You can override the default setting that is controlled by the duplex setting.

This proposal/agreement handshake is initiated only when a nonedge port moves from the blocking to the forwarding state. The handshaking process then proliferates step-by-step throughout the topology.

Related Concepts

Protocol Timers

This table describes the protocol timers that affect the Rapid PVST+ performance.


Table 2 Rapid PVST+ Protocol Timers

Variable

Description

Hello timer

Determines how often each device broadcasts BPDUs to other network devices. The default is 2 seconds, and the range is from 1 to 10.

Forward delay timer

Determines how long each of the listening and learning states last before the port begins forwarding. This timer is generally not used by the protocol, but it is used when interoperating with the 802.1D spanning tree. The default is 15 seconds, and the range is from 4 to 30 seconds.

Maximum age timer

Determines the amount of time that protocol information received on a port is stored by the network device. This timer is generally not used by the protocol, but it is used when interoperating with the 802.1D spanning tree. The default is 20 seconds; the range is from 6 to 40 seconds.

Port Roles

Rapid PVST+ provides rapid convergence of the spanning tree by assigning port roles and learning the active topology. Rapid PVST+ builds upon the 802.1D STP to select the device with the highest switch priority (lowest numerical priority value) as the root bridge. Rapid PVST+ assigns one of these port roles to individual ports:


  • Root port—Provides the best path (lowest cost) when the device forwards packets to the root bridge.

  • Designated port—Connects to the designated device that has the lowest path cost when forwarding packets from that LAN to the root bridge. The port through which the designated device is attached to the LAN is called the designated port.

  • Alternate port—Offers an alternate path toward the root bridge to the path provided by the current root port. An alternate port provides a path to another device in the topology.

  • Backup port—Acts as a backup for the path provided by a designated port toward the leaves of the spanning tree. A backup port can exist only when two ports are connected in a loopback by a point-to-point link or when a device has two or more connections to a shared LAN segment. A backup port provides another path in the topology to the device.

  • Disabled port—Has no role within the operation of the spanning tree.

In a stable topology with consistent port roles throughout the network, Rapid PVST+ ensures that every root port and designated port immediately transition to the forwarding state while all alternate and backup ports are always in the blocking state. Designated ports start in the blocking state. The port state controls the operation of the forwarding and learning processes.

This figure shows port roles. A port with the root or a designated port role is included in the active topology. A port with the alternate or backup port role is excluded from the active topology.
Figure 5. Sample Topology Demonstrating Port Roles

Related Concepts

Port States

Rapid PVST+ Port State Overview

Propagation delays can occur when protocol information passes through a switched LAN. As a result, topology changes can take place at different times and at different places in a switched network. When a Layer 2 LAN port transitions directly from nonparticipation in the spanning tree topology to the forwarding state, it can create temporary data loops. Ports must wait for new topology information to propagate through the switched LAN before starting to forward frames.

Each Layer 2 LAN port on the device that uses Rapid PVST+ or MST exists in one of the following four states:


  • Blocking—The Layer 2 LAN port does not participate in frame forwarding.

  • Learning—The Layer 2 LAN port prepares to participate in frame forwarding.

  • Forwarding—The Layer 2 LAN port forwards frames.

  • Disabled—The Layer 2 LAN port does not participate in STP and is not forwarding frames.

When you enable Rapid PVST+, every port in the device, VLAN, and network goes through the blocking state and the transitory states of learning at power up. If properly configured, each Layer 2 LAN port stabilizes to the forwarding or blocking state.

When the STP algorithm places a Layer 2 LAN port in the forwarding state, the following process occurs:


  1. The Layer 2 LAN port is put into the blocking state while it waits for protocol information that suggests it should go to the learning state.

  2. The Layer 2 LAN port waits for the forward delay timer to expire, moves the Layer 2 LAN port to the learning state, and restarts the forward delay timer.

  3. In the learning state, the Layer 2 LAN port continues to block frame forwarding as it learns the end station location information for the forwarding database.

  4. The Layer 2 LAN port waits for the forward delay timer to expire and then moves the Layer 2 LAN port to the forwarding state, where both learning and frame forwarding are enabled.

Blocking State

A Layer 2 LAN port in the blocking state does not participate in frame forwarding.

A Layer 2 LAN port in the blocking state performs as follows:


  • Discards frames received from the attached segment.

  • Discards frames switched from another port for forwarding.

  • Does not incorporate the end station location into its address database. (There is no learning on a blocking Layer 2 LAN port, so there is no address database update.)

  • Receives BPDUs and directs them to the system module.

  • Receives, processes, and transmits BPDUs received from the system module.

  • Receives and responds to control plane messages.

Learning State

A Layer 2 LAN port in the learning state prepares to participate in frame forwarding by learning the MAC addresses for the frames. The Layer 2 LAN port enters the learning state from the blocking state.

A Layer 2 LAN port in the learning state performs as follows:


  • Discards frames received from the attached segment.

  • Discards frames switched from another port for forwarding.

  • Incorporates the end station location into its address database.

  • Receives BPDUs and directs them to the system module.

  • Receives, processes, and transmits BPDUs received from the system module.

  • Receives and responds to control plane messages.

Forwarding State

A Layer 2 LAN port in the forwarding state forwards frames. The Layer 2 LAN port enters the forwarding state from the learning state.

A Layer 2 LAN port in the forwarding state performs as follows:


  • Forwards frames received from the attached segment.

  • Forwards frames switched from another port for forwarding.

  • Incorporates the end station location information into its address database.

  • Receives BPDUs and directs them to the system module.

  • Processes BPDUs received from the system module.

  • Receives and responds to control plane messages.

Disabled State

A Layer 2 LAN port in the disabled state does not participate in frame forwarding or STP. A Layer 2 LAN port in the disabled state is virtually nonoperational.

A disabled Layer 2 LAN port performs as follows:


  • Discards frames received from the attached segment.

  • Discards frames switched from another port for forwarding.

  • Does not incorporate the end station location into its address database. (There is no learning, so there is no address database update.)

  • Does not receive BPDUs from neighbors.

  • Does not receive BPDUs for transmission from the system module.

Summary of Port States

This table lists the possible operational and Rapid PVST+ states for ports and whether the port is included in the active topology.
Table 3  Port State Active Topology

Operational Status

Port State

Is Port Included in the Active Topology?

Enabled

Blocking

No

Enabled

Learning

Yes

Enabled

Forwarding

Yes

Disabled

Disabled

No

Synchronization of Port Roles

When the device receives a proposal message on one of its ports and that port is selected as the new root port, Rapid PVST+ forces all other ports to synchronize with the new root information.

The device is synchronized with superior root information received on the root port if all other ports are synchronized. An individual port on the device is synchronized if either of the following applies:


  • That port is in the blocking state.

  • It is an edge port (a port configured to be at the edge of the network).

If a designated port is in the forwarding state and is not configured as an edge port, it transitions to the blocking state when the Rapid PVST+ forces it to synchronize with new root information. In general, when the Rapid PVST+ forces a port to synchronize with root information and the port does not satisfy any of the above conditions, its port state is set to blocking.

After ensuring that all of the ports are synchronized, the device sends an agreement message to the designated device that corresponds to its root port. When the devices connected by a point-to-point link are in agreement about their port roles, Rapid PVST+ immediately transitions the port states to the forwarding state.

This figure shows the sequence of events during synchronization.
Figure 6. Sequence of Events During Rapid Convergence



Processing Superior BPDU Information

A superior BPDU is a BPDU with root information (such as a lower switch ID or lower path cost) that is superior to what is currently stored for the port.

If a port receives a superior BPDU, Rapid PVST+ triggers a reconfiguration. If the port is proposed and is selected as the new root port, Rapid PVST+ forces all the designated, nonedge ports to synchronize.

If the received BPDU is a Rapid PVST+ BPDU with the proposal flag set, the device sends an agreement message after all of the other ports are synchronized. The new root port transitions to the forwarding state as soon as the previous port reaches the blocking state.

If the superior information received on the port causes the port to become a backup port or an alternate port, Rapid PVST+ sets the port to the blocking state and sends an agreement message. The designated port continues sending BPDUs with the proposal flag set until the forward-delay timer expires. At that time, the port transitions to the forwarding state.

Processing Inferior BPDU Information

An inferior BPDU is a BPDU with root information (such as a higher switch ID or higher path cost) that is inferior to what is currently stored for the port.

If a designated port receives an inferior BPDU, it immediately replies with its own information.

Detecting Unidirectional Link Failure:Rapid PVST+

The software checks the consistency of the port role and state in the received BPDUs to detect unidirectional link failures that could cause bridging loops using the Unidirectional Link Detection (UDLD) feature. This feature is based on the dispute mechanism.

See the Interfaces Configuration Guide, Cisco DCNM for LAN, Release 5.x, for information on UDLD.

When a designated port detects a conflict, it keeps its role, but reverts to a discarding state because disrupting connectivity in case of inconsistency is preferable to opening a bridging loop.

This figure illustrates a unidirectional link failure that typically creates a bridging loop. Switch A is the root bridge, and its BPDUs are lost on the link leading to switch B. The 802.1w-standard BPDUs include the role and state of the sending port. With this information, switch A can detect that switch B does not react to the superior BPDUs that it sends and that switch B is the designated, not root port. As a result, switch A blocks (or keeps blocking) its port, which prevents the bridging loop.
Figure 7. Detecting Unidirectional Link Failure

Port Cost


Note


Rapid PVST+ uses the short (16-bit) path-cost method to calculate the cost by default. With the short path-cost method, you can assign any value in the range of 1 to 65535. However, you can configure the device to use the long (32-bit) path-cost method, which allows you to assign any value in the range of 1 to 200,000,000. You configure the path-cost calculation method globally.


This table shows how the STP port path-cost default value is determined from the media speed and path-cost calculation method of a LAN interface.
Table 4 Default Port Cost

Bandwidth

Short Path-Cost Method of Port Cost

Long Path-Cost Method of Port Cost

10 Mbps

100

2,000,000

100 Mbps

19

200,000

1 Gigabit Ethernet

4

20,000

10 Gigabit Ethernet

2

2,000

If a loop occurs, STP considers the port cost when selecting a LAN interface to put into the forwarding state.

You can assign the lower cost values to LAN interfaces that you want STP to select first and higher cost values to LAN interfaces that you want STP to select last. If all LAN interfaces have the same cost value, STP puts the LAN interface with the lowest LAN interface number in the forwarding state and blocks other LAN interfaces.

On access ports, you assign the port cost by the port. On trunk ports, you assign the port cost by the VLAN; you can configure the same port cost to all the VLANs on a trunk port.

Port Priority

If a redundant path occurs and multiple ports have the same path cost, Rapid PVST+ considers the port priority when selecting which LAN port to put into the forwarding state. You can assign lower priority values to LAN ports that you want Rapid PVST+ to select first and higher priority values to LAN ports that you want Rapid PVST+ to select last.

If all LAN ports have the same priority value, Rapid PVST+ puts the LAN port with the lowest LAN port number in the forwarding state and blocks other LAN ports. The possible priority range is from 0 through 224 (the default is 128), configurable in increments of 32. The device uses the port priority value when the LAN port is configured as an access port and uses the VLAN port priority values when the LAN port is configured as a trunk port.

Rapid PVST+ and IEEE 802.1Q Trunks

The 802.1Q trunks impose some limitations on the STP strategy for a network. In a network of Cisco network devices connected through 802.1Q trunks, the network devices maintain one instance of STP for each VLAN allowed on the trunks. However, non-Cisco 802.1Q network devices maintain only one instance of STP for all VLANs allowed on the trunks, which is the Common Spanning Tree (CST).

When you connect a Cisco network device to a non-Cisco device through an 802.1Q trunk, the Cisco network device combines the STP instance of the 802.1Q VLAN of the trunk with the STP instance of the non-Cisco 802.1Q network device. However, all per-VLAN STP information that is maintained by Cisco network devices is separated by a cloud of non-Cisco 802.1Q network devices. The non-Cisco 802.1Q cloud that separates the Cisco network devices is treated as a single trunk link between the network devices.

For more information on 802.1Q trunks, see the Interfaces Configuration Guide, Cisco DCNM for LAN, Release 5.x.

Rapid PVST+ Interoperation with Legacy 802.1D STP

Rapid PVST+ can interoperate with devices that are running the legacy 802.1D protocol. The device knows that it is interoperating with equipment running 802.1D when it receives a BPDU version 0. The BPDUs for Rapid PVST+ are version 2. If the BPDU received is an 802.1w BPDU version 2 with the proposal flag set, the device sends an agreement message after all of the other ports are synchronized. If the BPDU is an 802.1D BPDU version 0, the device does not set the proposal flag and starts the forward-delay timer for the port. The new root port requires twice the forward-delay time to transition to the forwarding state.

The device interoperates with legacy 802.1D devices as follows:


  • Notification—Unlike 802.1D BPDUs, 802.1w does not use TCN BPDUs. However, for interoperability with 802.1D devices, the device processes and generates TCN BPDUs.

  • Acknowledgment—When an 802.1w device receives a TCN message on a designated port from an 802.1D device, it replies with an 802.1D configuration BPDU with the TCA bit set. However, if the TC-while timer (the same as the TC timer in 802.1D) is active on a root port connected to an 802.1D device and a configuration BPDU with the TCA set is received, the TC-while timer is reset.

    This method of operation is required only for 802.1D devices. The 802.1w BPDUs do not have the TCA bit set.

  • Protocol migration—For backward compatibility with 802.1D devices, 802.1w selectively sends 802.1D configuration BPDUs and TCN BPDUs on a per-port basis.

    When a port is initialized, the migrate-delay timer is started (specifies the minimum time during which 802.1w BPDUs are sent), and 802.1w BPDUs are sent. While this timer is active, the device processes all BPDUs received on that port and ignores the protocol type.

    If the device receives an 802.1D BPDU after the port migration-delay timer has expired, it assumes that it is connected to an 802.1D device and starts using only 802.1D BPDUs. However, if the 802.1w device is using 802.1D BPDUs on a port and receives an 802.1w BPDU after the timer has expired, it restarts the timer and starts using 802.1w BPDUs on that port.

Rapid PVST+ Interoperation with 802.1s MST

Rapid PVST+ interoperates seamlessly with the IEEE 802.1s Multiple Spanning Tree (MST) standard. No user configuration is needed. To disable this seamless interoperation, you can use PVST Simulation.

High Availability for Rapid PVST+

The software supports high availability for Rapid PVST+. However, the statistics and timers are not restored when Rapid PVST+ restarts. The timers start again and the statistics begin from 0.


Note


See the Cisco Nexus 7000 Series NX-OS High Availability and Redundancy Guide, Release 5.x, for complete information on high-availability features.


Virtualization Support for Rapid PVST+


Note


See the Virtual Device Context Quick Start, Cisco DCNM for LAN, Release 5.x, for complete information on virtual device contexts (VDCs) and assigning resources.


This figure shows how the system provides support for VDCs. Using VDCs, you have a separate Layer 2 virtualization in each VDC, and each VDC runs a separate STP.

Each VDC will have its own Rapid PVST+. You cannot configure Rapid PVST+ across VDCs with Cisco NX-OS software. However, you can run Rapid PVST+ in one VDC and run MST in each VDC.

For example, VDC1 can run MST, VDC2 can run Rapid PVST+, and VDC3 can run MST.


Figure 8. Separate STP in each VDC

Licensing Requirements for Rapid PVST+

The following table shows the licensing requirements for this feature:

Product

License Requirement

Cisco DCNM

Rapid PVST+ requires no license. Any feature not included in a license package is bundled with the Cisco DCNM and is provided at no charge to you.

Cisco NX-OS

Rapid PVST+ requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see Cisco NX-OS Licensing Guide.

However, using VDCs requires an Advanced Services license.

Prerequisites for Configuring Rapid PVST+

Rapid PVST+ has the following prerequisites:


  • You must be logged onto the device.

Guidelines and Limitations for Configuring Rapid PVST+

Rapid PVST+ has the following configuration guidelines and limitations:


  • The maximum number of VLANs and ports is 16,000.

  • Only Rapid PVST+ or MST can be active at any time for each VDC.

  • Port channeling—The port-channel bundle is considered as a single port. The port cost is the aggregation of all the configured port costs assigned to that channel.

  • For Private VLANs, on a normal VLAN trunk port, the primary and secondary private VLANs are two different logical ports and must have the exact STP topology. On access ports, STP sees only the primary VLAN.

  • We recommend that you configure all ports connected to Layer 2 hosts as STP edge ports.

  • Always leave STP enabled.

  • Do not change timers because changing timers can adversely affect stability.

  • Keep user traffic off the management VLAN; keep the management VLAN separate from the user data.

  • Choose the distribution and core layers as the location of the primary and secondary root switches.

  • When you connect two Cisco devices through 802.1Q trunks, the switches exchange spanning tree BPDUs on each VLAN allowed on the trunks. The BPDUs on the native VLAN of the trunk are sent untagged to the reserved 802.1D spanning tree multicast MAC address (01-80-C2-00-00-00). The BPDUs on all VLANs on the trunk are sent tagged to the reserved Cisco Shared Spanning Tree Protocol (SSTP) multicast MAC address (01-00-0c-cc-cc-cd).

Platform Support for Rapid PVST+

The following platforms support this feature but may implement it differently. For platform-specific information, including guidelines and limitations, system defaults, and configuration limits, see the corresponding documentation.

Platform

Documentation

Cisco Nexus 7000 Series switches

Cisco Nexus 7000 Series switch documentation

Cisco Nexus 4000 Series switches

Cisco Nexus 4000 Series switch documentation

Cisco Nexus 5000 Series switches

Cisco Nexus 5000 Series switch documentation

Cisco Nexus 3000 Series switches

Cisco Nexus 3000 Series switch documentation

Cisco Catalyst 6500 Series switches

Cisco Catalyst 6500 Series switch documentation

Configuring Rapid PVST+


Note


See the , for information on using the Topology feature with MSTP.


Rapid PVST+, which has the 802.1 w standard applied to the PVST+ protocol, is the default STP setting in the device.

You enable Rapid PVST+ on a per-VLAN basis. The device maintains a separate instance of STP for each VLAN (except on those VLANs on which you disable STP). By default, Rapid PVST+ is enabled on the default VLAN and on each VLAN that you create.

Enabling Rapid PVST+

If you disable Rapid PVST+ on any VLANs, you must reenable Rapid PVST+ on the specified VLANs. If you have enabled MST on the device and now want to use Rapid PVST+, you must enable Rapid PVST+ on the device.

Rapid PVST+ is the default STP mode. You cannot simultaneously run MST and Rapid PVST+ in the same VDC.


Note


When you change the spanning tree mode, traffic is disrupted because all spanning tree instances are stopped for the previous mode and started for the new mode.


You enable Rapid PVST+ using the Spanning Tree pane shown in this figure.
Figure 9. Enabling Rapid PVST+



Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree to open the Spanning Tree pane.
Step 2   In the Summary pane, click the device on which you want to enable Rapid PVST+.

Rapid PVST+ is enabled on all VLANs by default.

Step 3   In the Protocol field, click the drop-down list and choose Rapid-PVST+.
Step 4   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Setting All STP Parameters on the Device to Default Values

You can set all the STP parameters on a device to default values, which set the STP mode to Rapid PVST+.

You use the Spanning Tree pane to set all STP parameters on the device to default values (see Figure 1).

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree to open the Spanning Tree pane.
Step 2   In the Summary pane, click the device that you want to set to STP default values.

Rapid PVST+ is the default STP mode.

Step 3   From the menu bar, choose Actions > Set to default.
Step 4   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Disabling or Enabling Rapid PVST+ per VLAN

You can enable or disable Rapid PVST+ on each VLAN.


Note


Rapid PVST+ is enabled by default on the default VLAN and on all VLANs that you create.


You use the Rapid-PVST+ pane shown in this figure to enable or disable Rapid PVST+ per VLAN.


Figure 10. Configuring Rapid PVST+

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid-PVST+ to open the Rapid-PVST+ pane.
Step 2   In the Summary pane, click the Device View tab.
Step 3   In the Summary pane, click the VLAN that you want to enable or disable. Rapid PVST+ is enabled on all VLANs by default.
Step 4   From the menu bar, choose Actions > Enable STP.
Note   

When you choose Actions > Manage VLAN, the system puts you back into the VLAN pane.

Step 5   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.


Note


Do not disable spanning tree on a VLAN unless all switches and bridges in the VLAN have spanning tree disabled. You cannot disable spanning tree on some switches and bridges in a VLAN and leave it enabled on other switches and bridges in the VLAN. This action can have unexpected results because switches and bridges with spanning tree enabled will have incomplete information regarding the physical topology of the network.



Caution


We do not recommend disabling spanning tree even in a topology that is free of physical loops. Spanning tree serves as a safeguard against misconfigurations and cabling errors. Do not disable spanning tree in a VLAN without ensuring that no physical loops are present in the VLAN.


Configuring the Primary and Secondary Roots and the Switch Priority for Rapid PVST+

The software maintains a separate instance of STP for each active VLAN in Rapid PVST+. For each VLAN, the network device with the lowest bridge ID becomes the root bridge for that VLAN.

You can configure the primary and secondary roots, or you can configure the switch priority for the specified VLAN so that it is more likely that the specified device is chosen as the root bridge.


Note


We recommend that you designate the primary and secondary roots, rather than choosing a specific value for the switch priority.


To configure multiple backup root bridges, designate more than one device as a secondary root. For the secondary root, use the same network diameter and hello-time values that you used when you configured the primary root bridge.

You use the Rapid-PVST+ pane to set the device to become the primary root bridge for the VLAN (see Figure 1).

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid-PVST+ to open the Rapid-PVST+ pane.
Step 2   In the Summary pane, click the Device View tab.
Step 3   In the Summary pane, click the VLAN for which you want to set the device as the primary root. Tabs appear in the Details pane.
Step 4   Click the Details tab.
Step 5   Click the VLAN Setting section. The VLAN Setting section has a Switch Priority area that allows you to set the device as the primary or secondary root for the specified VLAN, as well as setting the switch priority.
Step 6   (Optional)In the Root field, click the drop-down list and choose primary to make this device the primary root for the VLAN.
Step 7   (Optional)In the Root field, click the drop-down list and choose secondary to make this device the secondary root for the VLAN.
Step 8   (Optional) In the Switch Priority area, click the drop-down list in the Switch Priority field and choose the value that you want to set the device as the root switch for this VLAN. The default value is 32768.
Step 9   (Optional) In the Diameter field, click the drop-down list and choose the value that you want for the diameter. The default value for the diameter is 7.
Step 10   (Optional) In the Hello Time field, click the drop-down list and choose the number of seconds that you want between hello messages. The default for the hello time is 2 seconds.
Step 11   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Configuring the Rapid PVST+ Port Priority

You can assign lower priority values to LAN ports that you want Rapid PVST+ to select first and higher priority values to LAN ports that you want Rapid PVST+ to select last. If all LAN ports have the same priority value, Rapid PVST+ puts the LAN port with the lowest LAN port number in the forwarding state and blocks other LAN ports.

The device uses the port priority value when the LAN port is configured as an access port and uses the VLAN port priority values when the LAN port is configured as a trunk port.

You use the Rapid-PVST+ pane to assign port priority values in Rapid PVST+ (see Figure 1).

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid-PVST+ to open the Rapid-PVST+ pane.
Step 2   In the Summary pane, click the Device View tab.
Step 3   In the Summary pane, click the VLAN with the ports for which you want to set the priority. Tabs appear in the Details pane.
Step 4   Click the Details tab.
Step 5   Click the Port Setting section.
Step 6   Click the port for which you want to set the priority.
Step 7   In the Priority field, click the drop-down list and choose the value that you want for the Rapid PVST+ priority for that port. The default value is 128.
Step 8   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Configuring the Rapid PVST+ Path-Cost Method and Port Cost

On access ports, you can assign the port cost for each port. On trunk ports, you can assign the port cost for each VLAN and you can configure all the VLANs on a trunk with the same port cost.


Note


In Rapid PVST+ mode, you can use either the short or long path-cost method, and you can configure the method in either the interface or configuration submode. The default path-cost method is short.


You use the Spanning Tree pane to configure the path-cost method for Rapid PVST+ (see Figure 1).

You use the Rapid-PVST+ pane to set the Rapid PVST+ cost for a port (see Figure 1).

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree to open the Spanning Tree pane.
Step 2   In the Summary pane, click the device that you want. Tabs appear in the Details pane.
Step 3   Click the Configuration tab.
Step 4   Click the Global Setting section.
Step 5   In the Path Cost field, choose long or short for the path-cost method. The default path-cost method is short.
Step 6   From the menu bar, choose File > Deploy to apply your changes to the device.
Step 7   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid-PVST+ to open the Rapid-PVST+ pane.
Step 8   In the Summary pane, click the Device View tab.
Step 9   In the Summary pane, click the VLAN with the ports for which you want to set the priority. Tabs appear in the Details pane.
Step 10   Click the Details tab.
Step 11   Click the Port Setting section.
Step 12   Click the port for which you want to set the cost.
Step 13   In the Cost field, click auto to disable the cost for that port.
Step 14   Enter a value to set the cost for the port. Valid values for the short path-cost method, which is the default method, are from 1 to 65535. Valid values for the long path-cost method are from 1 to 200000000. The default port cost is determined by the port’s bandwidth.
Step 15   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Setting All Rapid PVST+ Parameters to Default Values per Interface

You can use the Rapid-PVST+ pane shown in this figure to reset all STP parameters on the selected interface for the selected VLAN on the device to default Rapid PVST+ values.
Figure 11. Setting Rapid PVST+ Values

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid PVST+ to open the Rapid-PVST+ pane.
Step 2   In the Summary pane, click the Network View tab.
Step 3   In the Summary pane, click the device that you want. The devices that carry that VLAN appear.
Step 4   Click the device. The system highlights the device in the Summary pane, and tabs appear in the Details pane.
Step 5   In the Details pane, click the Details tab.
Step 6   In the Details tab, click the Port Setting section. The interfaces in the VLAN on the selected device appear.
Step 7   Click the interface. The system highlights the selected interface.
Step 8   From the menu bar, choose Actions > Set to default.
Step 9   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Configuring the Rapid PVST+ Hello Time for a VLAN

You can configure the Rapid PVST+ hello time for a VLAN.


Note


Be careful when using this configuration; you may disrupt the Spanning Tree. For most situations, we recommend that you configure the primary root and secondary root to modify the hello time.


Before You Begin

When you configure virtual port channels (vPCs) on the switch, we recommend that you set the STP hello time to 4 seconds on both the primary and secondary vPC peer devices.

For more information on vPCs, see the Interfaces Configuration Guide, Cisco DCNM for LAN, Release 5.x.

You can use the Rapid-PVST+ pane to configure the hello time for the VLAN (see Figure 1).


Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid-PVST+ to open the Rapid-PVST+ pane.
Step 2   In the Summary pane, click the Device View tab.
Step 3   In the Summary pane, click the VLAN for which you want to set the hello time. Tabs appear in the Details pane.
Step 4   Click the Details tab.
Step 5   Click the VLAN Settings section.
Step 6   In the Hello Time field, click the drop-down list and choose the number of seconds that you want between hello messages. The default for the hello time is 2 seconds.
Step 7   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Configuring the Rapid PVST+ Forward Delay Time for a VLAN

You can configure the forward delay time per VLAN when using Rapid PVST+.

You use the Rapid-PVST+ pane to configure the forward delay time for the VLAN (see Figure 1).

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid-PVST+ to open the Rapid-PVST+ pane.
Step 2   In the Summary pane, click the Device View tab.
Step 3   In the Summary pane, click the VLAN for which you want to set the hello time. Tabs appear in the Details pane.
Step 4   Click the Details tab.
Step 5   Click the VLAN Setting section.
Step 6   In the Forward Delay Time field, enter the number of seconds that you want for the forward delay value. The default for the forward delay time is 15 seconds.
Step 7   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Configuring the Rapid PVST+ Maximum Age Time for a VLAN

You can configure the maximum age time per VLAN when using Rapid PVST+.

You use the Rapid-PVST+pane to configure the maximum age time for the VLAN (see Figure 1).

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Rapid-PVST+ to open the Rapid-PVST+ pane.
Step 2   In the Summary pane, click the Device View tab.
Step 3   In the Summary pane, click the VLAN for which you want to set the hello time. Tabs appear in the Details pane.
Step 4   Click the Details tab.
Step 5   Click the VLAN Setting section.
Step 6   In the Max Age Time field, enter the number of seconds that you want before the BPDUs age out. The default for the maximum age time is 20 seconds.
Step 7   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Specifying the Link Type for Rapid PVST+

Rapid connectivity (802.1w standard) is established only on point-to-point links. By default, the link type is controlled from the duplex mode of the interface. A full-duplex port is considered to have a point-to-point connection; a half-duplex port is considered to have a shared connection.

If you have a half-duplex link physically connected point to point to a single port on a remote device, you can override the default setting on the link type and enable rapid transitions.

If you set the link to shared, STP falls back to 802.1D.

You can use the Spanning Tree pane to set the link type (see Figure 1).

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree to open the Spanning Tree pane.
Step 2   In the Summary pane, click the device.
Step 3   In the Details pane, click the Configuration tab.
Step 4   In the Details pane, click the Port Setting section. The Port Setting section expands.
Step 5   In the Port Setting section, click the interface that you want to configure.
Step 6   In the Link Type column, click the drop-down list and choose the link type. The default Link Type is Auto.
Step 7   (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.

Displaying Rapid PVST+ Statistics

The following window appears in the Statistics tab:


  • Spanning Tree Statistics—Displays information on Rapid PVST+, including BPDUs sent and received.

Field Descriptions for Rapid PVST+

The field descriptions are used for configuring Rapid PVST+.

Device View: VLAN: Details: VLAN Setting Section

Table 5 Device View: VLAN: Details: VLAN Setting Section

Field

Description

VLAN

Display only. Number that uniquely identifies the VLAN.

Device

Display only. Name of the device.

Name

Display only. Name of the VLAN, The default name is VLANXXXX.

Type

Display only. Type of VLAN. Valid values are as follows:


  • Normal

  • Primary

  • Secondary

Status

Display only. Operational status of STP in the VLAN.

Root Bridge MAC Address

Display only. MAC address of the root bridge.

Hello Time

Period between device broadcasting hello messages. The default value is 2 seconds.

Forward Delay Time

Period that the learning state lasts before the port begins forwarding. The default value is 15 seconds.

Max Age Time

Amount of time that protocol information is stored on a port. The default value is 20 seconds.

STP

Status of whether STP is enabled or disabled on the VLAN. The default value is Enabled.

Switch Priority

Switch Priority

Priority of the bridge. The default value is 32768.

Root

Primary or secondary root for Rapid PVST+. The default is blank.

Diameter

Maximum allowed hops between any two end stations in a Layer 2 network. The default is blank.

Hello Time

Period between broadcasting hello messages. The default is blank.

Port Status

Total Ports

Display only. Number of ports that are part of the VLAN.

Blocking Ports

Display only. Number of ports in the VLAN that are in the STP blocking state.

Forwarding Ports

Display only. Number of ports in the VLAN that are in the STP forwarding state.

Device View: VLAN: Details: Port Setting Section

Table 6  Device View: VLAN: Details: Port Setting Section

Field

Description

Name

Display only. Name of the port.

Mode

Display only. Port mode.

Configuration

Priority

STP port priority. The default value is 128.

Cost


  • Auto—STP port cost derived from media speed of interface.

  • Value—Manually configured port cost. Valid values are 1 to 200000000.

Status

Role

Display only. Rapid PVST+ port role. Valid values are as follows:


  • Root port

  • Designated port

  • Alternate port

  • Backup port

  • Disabled

State

Display only. Rapid PVST+ port state. Valid values are as follows:


  • Blocking

  • Learning

  • Forwarding

  • Disabled

Priority

Display only. STP port priority. The default value is 128.

Cost

Display only. STP port cost. The value is derived from the media speed of the interface; valid values are 1 to 200000000.

Link Type

Display only. Type of link. The default is auto.

Network View: Device: Details: VLAN Setting Section

Table 7 Network View: Device: Details: VLAN Setting Section

Field

Description

VLAN

Display only. Number that uniquely identifies the VLAN.

Device

Display only. Name of the device.

Name

Display only. Name of the VLAN. The default name is VLANXXXX.

Type

Display only. Type of VLAN. Valid values are as follows:


  • Normal

  • Primary

  • Secondary

Status

Display only. Operational status of STP in the VLAN.

Root Bridge MAC Address

Display only. MAC address of the root bridge.

Hello Time

Period between device broadcasting hello messages. The default value is 2 seconds.

Forward Delay Time

Period that the learning state lasts before the port begins forwarding. The default value is 15 seconds.

Max Age Time

Amount of time that protocol information is stored on a port. The default value is 20 seconds.

STP

Status of whether STP is enabled or disabled on the VLAN. The default value is Enabled.

Switch Priority

Switch Priority

Priority of the bridge. The default value is 32768.

Root

Primary or secondary root for Rapid PVST+. The default is blank.

Diameter

Maximum allowed hops between any two end stations in a Layer 2 network. The default is blank.

Hello Time

Period between broadcasting hello messages. The default is blank.

Port Status

Total Ports

Display only. Number of ports that are part of the VLAN.

Blocking Ports

Display only. Number of ports in the VLAN that are in the STP blocking state.

Forwarding Ports

Display only. Number of ports in the VLAN that are in the STP forwarding state.

Network View: Device: Details: Port Setting Section

Table 8  Network View: Device: Details: Port Setting Section

Field

Description

Name

Display only. Name of the port.

Mode

Display only. Port mode.

Configuration

Priority

STP port priority. The default value is 128.

Cost


  • Auto—STP port cost derived from media speed of interface.

  • Value—Manually configured port cost. Valid values are 1 to 200000000.

Status

Role

Display only. Rapid PVST+ port role. Valid values are as follows:


  • Root port

  • Designated port

  • Alternate port

  • Backup port

  • Disabled

State

Display only. Rapid PVST+ port state. Valid values are as follows:


  • Blocking

  • Learning

  • Forwarding

  • Disabled

Priority

Display only. STP port priority. The default value is 128.

Cost

Display only. STP port cost. The value is derived from the media speed of the interface; valid values are 1 to 200000000.

Link Type

Display only. Type of link. Valid values are shared and point-to-point.

Additional References for Rapid PVST+—DCNM Version

Related Documents

Related Topic

Document Title

Layer 2 interfaces

Interfaces Configuration Guide, Cisco DCNM for LAN, Release 5.x

VDCs

Virtual Device Context Configuration Guide, Cisco DCNM for LAN, Release 5.x

Standards

Standards

Title

IEEE 802.1Q-2006 (formerly known as IEEE 802.1s), IEEE 802.1D-2004 (formerly known as IEEE 802.1w), IEEE 802.1D, IEEE 802.1t

MIBs

MIBs

MIBs Link


  • CISCO-STP-EXTENSION-MIB

  • BRIDGE-MIB

To locate and download MIBs, go to the following URL:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

Feature History for Configuring Rapid PVST+

This table lists the release history for this feature.
Table 9 Feature History for Configuring Rapid PVST+

Feature Name

Releases

Feature Information

There are no changes.

4.1(2)