- Preface
- Using the Command-Line Interface
- Configuring Spanning Tree Protocol
- Configuring Multiple Spanning-Tree Protocol
- Configuring Optional Spanning-Tree Features
- Configuring EtherChannels
- Configuring Flex Links and the MAC Address-Table Move Update Feature
- Configuring UniDirectional Link Detection
- Index
- Finding Feature Information
- Restrictions for STP
- Information About Spanning Tree Protocol
- Spanning Tree Protocol
- Spanning-Tree Topology and BPDUs
- Bridge ID, Device Priority, and Extended System ID
- Port Priority Versus Path Cost
- Spanning-Tree Interface States
- How a Switch or Port Becomes the Root Switch or Root Port
- Spanning Tree and Redundant Connectivity
- Spanning-Tree Address Management
- Accelerated Aging to Retain Connectivity
- Spanning-Tree Modes and Protocols
- Supported Spanning-Tree Instances
- Spanning-Tree Interoperability and Backward Compatibility
- STP and IEEE 802.1Q Trunks
- VLAN-Bridge Spanning Tree
- Spanning Tree and Switch Stacks
- Default Spanning-Tree Configuration
- Spanning Tree Protocol
- How to Configure Spanning-Tree Features
- Changing the Spanning-Tree Mode
- Disabling Spanning Tree
- Configuring the Root Switch
- Configuring a Secondary Root Device
- Configuring Port Priority
- Configuring Path Cost
- Configuring the Device Priority of a VLAN
- Configuring the Hello Time
- Configuring the Forwarding-Delay Time for a VLAN
- Configuring the Maximum-Aging Time for a VLAN
- Configuring the Transmit Hold-Count
- Monitoring Spanning-Tree Status
- Additional References for Spanning-Tree Protocol
- Feature Information for STP
Configuring Spanning Tree Protocol
- Finding Feature Information
- Restrictions for STP
- Information About Spanning Tree Protocol
- How to Configure Spanning-Tree Features
- Monitoring Spanning-Tree Status
- Additional References for Spanning-Tree Protocol
- Feature Information for STP
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Restrictions for STP
- An attempt to configure a switch as the root switch fails if the value necessary to be the root switch is less than 1.
- If your network consists of switches that support and do not support the extended system ID, it is unlikely that the switch with the extended system ID support will become the root switch. The extended system ID increases the switch priority value every time the VLAN number is greater than the priority of the connected switches running older software.
- The root switch for each spanning-tree instance should be a backbone or distribution switch. Do not configure an access switch as the spanning-tree primary root.
- You cannot have a switch stack containing a mix of Catalyst 3850 and Catalyst 3650 switches.
Information About Spanning Tree Protocol
Spanning Tree Protocol
Spanning Tree Protocol (STP) is a Layer 2 link management protocol that provides path redundancy while preventing loops in the network. For a Layer 2 Ethernet network to function properly, only one active path can exist between any two stations. Multiple active paths among end stations cause loops in the network. If a loop exists in the network, end stations might receive duplicate messages. Switches might also learn end-station MAC addresses on multiple Layer 2 interfaces. These conditions result in an unstable network. Spanning-tree 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.
The STP uses a spanning-tree algorithm to select one switch of a redundantly connected network as the root of the spanning tree. The algorithm calculates the best loop-free path through a switched Layer 2 network by assigning a role to each port based on the role of the port in the active topology:
- Root—A forwarding port elected for the spanning-tree topology
- Designated—A forwarding port elected for every switched LAN segment
- Alternate—A blocked port providing an alternate path to the root bridge in the spanning tree
- Backup—A blocked port in a loopback configuration
The switch that has all of its ports as the designated role or as the backup role is the root switch. The switch that has at least one of its ports in the designated role is called the designated switch.
Spanning tree forces redundant data paths into a standby (blocked) state. If a network segment in the spanning tree fails and a redundant path exists, the spanning-tree algorithm recalculates the spanning-tree topology and activates the standby path. Switches send and receive spanning-tree frames, called bridge protocol data units (BPDUs), at regular intervals. The switches do not forward these frames but use them to construct a loop-free path. BPDUs contain information about the sending switch and its ports, including switch and MAC addresses, switch priority, port priority, and path cost. Spanning tree uses this information to elect the root switch and root port for the switched network and the root port and designated port for each switched segment.
When two ports on a switch are part of a loop, the spanning-tree and path cost settings control which port is put in the forwarding state and which is put in the blocking state. The spanning-tree port priority value represents the location of a port in the network topology and how well it is located to pass traffic. The path cost value represents the media speed.
- Spanning-Tree Topology and BPDUs
- Bridge ID, Device Priority, and Extended System ID
- Port Priority Versus Path Cost
- Spanning-Tree Interface States
- How a Switch or Port Becomes the Root Switch or Root Port
- Spanning Tree and Redundant Connectivity
- Spanning-Tree Address Management
- Accelerated Aging to Retain Connectivity
- Spanning-Tree Modes and Protocols
- Supported Spanning-Tree Instances
- Spanning-Tree Interoperability and Backward Compatibility
- STP and IEEE 802.1Q Trunks
- VLAN-Bridge Spanning Tree
- Spanning Tree and Switch Stacks
Spanning-Tree Topology and BPDUs
The stable, active spanning-tree topology of a switched network is controlled by these elements:
- The unique bridge ID (switch priority and MAC address) associated with each VLAN on each switch. In a switch stack, all switches use the same bridge ID for a given spanning-tree instance.
- The spanning-tree path cost to the root switch.
- The port identifier (port priority and MAC address) associated with each Layer 2 interface.
When the switches in a network are powered up, each functions as the root switch. Each switch sends a configuration BPDU through all of its ports. The BPDUs communicate and compute the spanning-tree topology. Each configuration BPDU contains this information:
- The unique bridge ID of the switch that the sending switch identifies as the root switch
- The spanning-tree path cost to the root
- The bridge ID of the sending switch
- Message age
- The identifier of the sending interface
- Values for the hello, forward delay, and max-age protocol timers
When a switch receives a configuration BPDU that contains superior information (lower bridge ID, lower path cost, and so forth), it stores the information for that port. If this BPDU is received on the root port of the switch, the switch also forwards it with an updated message to all attached LANs for which it is the designated switch.
If a switch receives a configuration BPDU that contains inferior information to that currently stored for that port, it discards the BPDU. If the switch is a designated switch for the LAN from which the inferior BPDU was received, it sends that LAN a BPDU containing the up-to-date information stored for that port. In this way, inferior information is discarded, and superior information is propagated on the network.
A BPDU exchange results in these actions:
- One switch in the network is elected as the root switch (the logical center of the spanning-tree topology in a switched network). See the figure following the bullets. For each VLAN, the switch with the highest switch priority (the lowest numerical priority value) is elected as the root switch. If all switches are configured with the default priority (32768), the switch with the lowest MAC address in the VLAN becomes the root switch. The switch priority value occupies the most significant bits of the bridge ID, as shown in the following figure.
- A root port is selected for each switch (except the root switch). This port provides the best path (lowest cost) when the switch forwards packets to the root switch. When selecting the root port on a switch stack, spanning tree follows this sequence:
- Only one outgoing port on the stack root switch is selected as the root port. The remaining switches in the stack become its designated switches (Switch 2 and Switch 3) as shown in the following figure.
- The shortest distance to the root switch is calculated for each switch based on the path cost.
- A designated switch for each LAN segment is selected. The designated switch incurs the lowest path cost when forwarding packets from that LAN to the root switch. The port through which the designated switch is attached to the LAN is called the designated port.
All paths that are not needed to reach the root switch from anywhere in the switched network are placed in the spanning-tree blocking mode.
Bridge ID, Device Priority, and Extended System ID
The IEEE 802.1D standard requires that each switch has an unique bridge identifier (bridge ID), which controls the selection of the root switch. Because each VLAN is considered as a different logical bridge with PVST+ and Rapid PVST+, the same switch must have a different bridge ID for each configured VLAN. Each VLAN on the switch has a unique 8-byte bridge ID. The 2 most-significant bytes are used for the switch priority, and the remaining 6 bytes are derived from the switch MAC address.
The switch supports the IEEE 802.1t spanning-tree extensions, and some of the bits previously used for the switch priority are now used as the VLAN identifier. The result is that fewer MAC addresses are reserved for the switch, and a larger range of VLAN IDs can be supported, all while maintaining the uniqueness of the bridge ID.
Spanning tree uses the extended system ID, the switch priority, and the allocated spanning-tree MAC address to make the bridge ID unique for each VLAN. Because the switch stack appears as a single switch to the rest of the network, all switches in the stack use the same bridge ID for a given spanning tree. If the stack master fails, the stack members recalculate their bridge IDs of all running spanning trees based on the new MAC address of the new stack master.
Support for the extended system ID affects how you manually configure the root switch, the secondary root switch, and the switch priority of a VLAN. For example, when you change the switch priority value, you change the probability that the switch will be elected as the root switch. Configuring a higher value decreases the probability; a lower value increases the probability.
If any root switch for the specified VLAN has a switch priority lower than 24576, the switch sets its own priority for the specified VLAN to 4096 less than the lowest switch priority. 4096 is the value of the least-significant bit of a 4-bit switch priority value as shown in the table.
Port Priority Versus Path Cost
If a loop occurs, spanning tree uses port priority when selecting an interface to put into the forwarding state. You can assign higher priority values (lower numerical values) to interfaces that you want selected first and lower priority values (higher numerical values) that you want selected last. If all interfaces have the same priority value, spanning tree puts the interface with the lowest interface number in the forwarding state and blocks the other interfaces.
The spanning-tree path cost default value is derived from the media speed of an interface. If a loop occurs, spanning tree uses cost when selecting an interface to put in the forwarding state. You can assign lower cost values to interfaces that you want selected first and higher cost values that you want selected last. If all interfaces have the same cost value, spanning tree puts the interface with the lowest interface number in the forwarding state and blocks the other interfaces.
If your switch is a member of a switch stack, you must assign lower cost values to interfaces that you want selected first and higher cost values that you want selected last instead of adjusting its port priority. For details, see Related Topics.
Spanning-Tree Interface States
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 an interface transitions directly from nonparticipation in the spanning-tree topology to the forwarding state, it can create temporary data loops. Interfaces must wait for new topology information to propagate through the switched LAN before starting to forward frames. They must allow the frame lifetime to expire for forwarded frames that have used the old topology.
Each Layer 2 interface on a switch using spanning tree exists in one of these states:
- Blocking—The interface does not participate in frame forwarding.
- Listening—The first transitional state after the blocking state when the spanning tree decides that the interface should participate in frame forwarding.
- Learning—The interface prepares to participate in frame forwarding.
- Forwarding—The interface forwards frames.
- Disabled—The interface is not participating in spanning tree because of a shutdown port, no link on the port, or no spanning-tree instance running on the port.
An interface moves through these states:
- From initialization to blocking
- From blocking to listening or to disabled
- From listening to learning or to disabled
- From learning to forwarding or to disabled
- From forwarding to disabled
When you power up the switch, spanning tree is enabled by default, and every interface in the switch, VLAN, or network goes through the blocking state and the transitory states of listening and learning. Spanning tree stabilizes each interface at the forwarding or blocking state.
When the spanning-tree algorithm places a Layer 2 interface in the forwarding state, this process occurs:
- The interface is in the listening state while spanning tree waits for protocol information to move the interface to the blocking state.
- While spanning tree waits for the forward-delay timer to expire, it moves the interface to the learning state and resets the forward-delay timer.
- In the learning state, the interface continues to block frame forwarding as the switch learns end-station location information for the forwarding database.
- When the forward-delay timer expires, spanning tree moves the interface to the forwarding state, where both learning and frame forwarding are enabled.
Blocking State
A Layer 2 interface in the blocking state does not participate in frame forwarding. After initialization, a BPDU is sent to each switch interface. A switch initially functions as the root until it exchanges BPDUs with other switches. This exchange establishes which switch in the network is the root or root switch. If there is only one switch in the network, no exchange occurs, the forward-delay timer expires, and the interface moves to the listening state. An interface always enters the blocking state after switch initialization.
An interface in the blocking state performs these functions:
Listening State
The listening state is the first state a Layer 2 interface enters after the blocking state. The interface enters this state when the spanning tree decides that the interface should participate in frame forwarding.
An interface in the listening state performs these functions:
Learning State
A Layer 2 interface in the learning state prepares to participate in frame forwarding. The interface enters the learning state from the listening state.
An interface in the learning state performs these functions:
Forwarding State
A Layer 2 interface in the forwarding state forwards frames. The interface enters the forwarding state from the learning state.
An interface in the forwarding state performs these functions:
Disabled State
A Layer 2 interface in the disabled state does not participate in frame forwarding or in the spanning tree. An interface in the disabled state is nonoperational.
How a Switch or Port Becomes the Root Switch or Root Port
If all switches in a network are enabled with default spanning-tree settings, the switch with the lowest MAC address becomes the root switch.
When the spanning-tree topology is calculated based on default parameters, the path between source and destination end stations in a switched network might not be ideal. For instance, connecting higher-speed links to an interface that has a higher number than the 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 Gigabit Ethernet link and that another port on Switch B (a 10/100 link) is the root port. Network traffic might be more efficient over the Gigabit Ethernet link. By changing the spanning-tree port priority on the Gigabit Ethernet port to a higher priority (lower numerical value) than the root port, the Gigabit Ethernet port becomes the new root port.
Spanning Tree and Redundant Connectivity
You can also create redundant links between switches by using EtherChannel groups.
Spanning-Tree Address Management
IEEE 802.1D specifies 17 multicast addresses, ranging from 0x00180C2000000 to 0x0180C2000010, to be used by different bridge protocols. These addresses are static addresses that cannot be removed.
Regardless of the spanning-tree state, each switch in the stack receives but does not forward packets destined for addresses between 0x0180C2000000 and 0x0180C200000F.
If spanning tree is enabled, the CPU on the switch or on each switch in the stack receives packets destined for 0x0180C2000000 and 0x0180C2000010. If spanning tree is disabled, the switch or each switch in the stack forwards those packets as unknown multicast addresses.
Accelerated Aging to Retain Connectivity
The default for aging dynamic addresses is 5 minutes, the default setting of the mac address-table aging-time global configuration command. However, a spanning-tree reconfiguration can cause many station locations to change. Because these stations could be unreachable for 5 minutes or more during a reconfiguration, the address-aging time is accelerated so that station addresses can be dropped from the address table and then relearned. The accelerated aging is the same as the forward-delay parameter value ( spanning-tree vlan vlan-id forward-time seconds global configuration command) when the spanning tree reconfigures.
Because each VLAN is a separate spanning-tree instance, the switch accelerates aging on a per-VLAN basis. A spanning-tree reconfiguration on one VLAN can cause the dynamic addresses learned on that VLAN to be subject to accelerated aging. Dynamic addresses on other VLANs can be unaffected and remain subject to the aging interval entered for the switch.
Spanning-Tree Modes and Protocols
The switch supports these spanning-tree modes and protocols:
- PVST+—This spanning-tree mode is based on the IEEE 802.1D standard and Cisco proprietary extensions. It is the default spanning-tree mode used on all Ethernet port-based VLANs. The PVST+ runs on each VLAN on the switch up to the maximum supported, ensuring that each has a loop-free path through the network. The PVST+ provides Layer 2 load-balancing for the VLAN on which it runs. You can create different logical topologies by using the VLANs on your network to ensure that all of your links are used but that no one link is oversubscribed. Each instance of PVST+ on a VLAN has a single root switch. This root switch propagates the spanning-tree information associated with that VLAN to all other switches in the network. Because each switch has the same information about the network, this process ensures that the network topology is maintained.
- Rapid PVST+—This spanning-tree mode is the same as PVST+ except that is uses a rapid convergence based on the IEEE 802.1w standard. To provide rapid convergence, the Rapid PVST+ immediately deletes dynamically learned MAC address entries on a per-port basis upon receiving a topology change. By contrast, PVST+ uses a short aging time for dynamically learned MAC address entries. Rapid PVST+ uses the same configuration as PVST+ (except where noted), and the switch needs only minimal extra configuration. The benefit of Rapid PVST+ is that you can migrate a large PVST+ install base to Rapid PVST+ without having to learn the complexities of the Multiple Spanning Tree Protocol (MSTP) configuration and without having to reprovision your network. In Rapid PVST+ mode, each VLAN runs its own spanning-tree instance up to the maximum supported.
- MSTP—This spanning-tree mode is based on the IEEE 802.1s standard. You can map multiple VLANs to the same spanning-tree instance, which reduces the number of spanning-tree instances required to support a large number of VLANs. The MSTP runs on top of the RSTP (based on IEEE 802.1w), which provides for rapid convergence of the spanning tree by eliminating the forward delay and by quickly transitioning root ports and designated ports to the forwarding state. In a switch stack, the cross-stack rapid transition (CSRT) feature performs the same function as RSTP. You cannot run MSTP without RSTP or CSRT.
Supported Spanning-Tree Instances
In PVST+ or Rapid PVST+ mode, the switch or switch stack supports up to 128 spanning-tree instances.
In MSTP mode, the switch or switch stack supports up to 65 MST instances. The number of VLANs that can be mapped to a particular MST instance is unlimited.
Spanning-Tree Interoperability and Backward Compatibility
STP and IEEE 802.1Q Trunks
The IEEE 802.1Q standard for VLAN trunks imposes some limitations on the spanning-tree strategy for a network. The standard requires only one spanning-tree instance for all VLANs allowed on the trunks. However, in a network of Cisco switches connected through IEEE 802.1Q trunks, the switches maintain one spanning-tree instance for each VLAN allowed on the trunks.
When you connect a Cisco switch to a non-Cisco device through an IEEE 802.1Q trunk, the Cisco switch uses PVST+ to provide spanning-tree interoperability. If Rapid PVST+ is enabled, the switch uses it instead of PVST+. The switch combines the spanning-tree instance of the IEEE 802.1Q VLAN of the trunk with the spanning-tree instance of the non-Cisco IEEE 802.1Q switch.
However, all PVST+ or Rapid PVST+ information is maintained by Cisco switches separated by a cloud of non-Cisco IEEE 802.1Q switches. The non-Cisco IEEE 802.1Q cloud separating the Cisco switches is treated as a single trunk link between the switches.
PVST+ is automatically enabled on IEEE 802.1Q trunks, and no user configuration is required. The external spanning-tree behavior on access ports and Inter-Switch Link (ISL) trunk ports is not affected by PVST+.
VLAN-Bridge Spanning Tree
Cisco VLAN-bridge spanning tree is used with the fallback bridging feature (bridge groups), which forwards non-IP protocols such as DECnet between two or more VLAN bridge domains or routed ports. The VLAN-bridge spanning tree allows the bridge groups to form a spanning tree on top of the individual VLAN spanning trees to prevent loops from forming if there are multiple connections among VLANs. It also prevents the individual spanning trees from the VLANs being bridged from collapsing into a single spanning tree.
To support VLAN-bridge spanning tree, some of the spanning-tree timers are increased. To use the fallback bridging feature, you must have the IP services feature set enabled on your switch.
Spanning Tree and Switch Stacks
When the switch stack is operating in PVST+ or Rapid PVST+ mode:
- A switch stack appears as a single spanning-tree node to the rest of the network, and all stack members use the same bridge ID for a given spanning tree. The bridge ID is derived from the MAC address of the active switch.
- When a new switch joins the stack, it sets its bridge ID to the active switch bridge ID. If the newly added switch has the lowest ID and if the root path cost is the same among all stack members, the newly added switch becomes the stack root.
- When a stack member leaves the stack, spanning-tree reconvergence occurs within the stack (and possibly outside the stack). The remaining stack member with the lowest stack port ID becomes the stack root.
- If the switch stack is the spanning-tree root and the active switch fails or leaves the stack, the standby switch becomes the new active switch, bridge IDs remain the same, and a spanning-tree reconvergence might occur.
- If a neighboring switch external to the switch stack fails or is powered down, normal spanning-tree processing occurs. Spanning-tree reconvergence might occur as a result of losing a switch in the active topology.
- If a new switch external to the switch stack is added to the network, normal spanning-tree processing occurs. Spanning-tree reconvergence might occur as a result of adding a switch in the network.
Default Spanning-Tree Configuration
How to Configure Spanning-Tree Features
Changing the Spanning-Tree Mode
The switch supports three spanning-tree modes: per-VLAN spanning tree plus (PVST+), Rapid PVST+, or multiple spanning tree protocol (MSTP). By default, the switch runs the PVST+ protocol.
If you want to enable a mode that is different from the default mode, this procedure is required.
Beginning in privileged EXEC mode, follow these steps to change the spanning-tree mode:
DETAILED STEPS
Disabling Spanning Tree
Spanning tree is enabled by default on VLAN 1 and on all newly created VLANs up to the spanning-tree limit. Disable spanning tree only if you are sure there are no loops in the network topology.
Caution |
When spanning tree is disabled and loops are present in the topology, excessive traffic and indefinite packet duplication can drastically reduce network performance. |
Beginning in privileged EXEC mode, follow these steps to disable a spanning tree:
DETAILED STEPS
Configuring the Root Switch
To configure a switch as the root for the specified VLAN, use the spanning-tree vlan vlan-id root global configuration command to modify the switch priority from the default value (32768) to a significantly lower value. When you enter this command, the software checks the switch priority of the root switches for each VLAN. Because of the extended system ID support, the switch sets its own priority for the specified VLAN to 24576 if this value will cause this switch to become the root for the specified VLAN.
Use the diameter keyword to specify the Layer 2 network diameter (that is, the maximum number of switch hops between any two end stations in the Layer 2 network). When you specify the network diameter, the switch automatically sets an optimal hello time, forward-delay time, and maximum-age time for a network of that diameter, which can significantly reduce the convergence time. You can use the hello keyword to override the automatically calculated hello time.
Beginning in privileged EXEC mode, follow these steps to configure a switch to become the root for the specified VLAN:
DETAILED STEPS
After configuring the switch as the root switch, we recommend that you avoid manually configuring the hello time, forward-delay time, and maximum-age time through the spanning-tree vlan vlan-id hello-time, spanning-tree vlan vlan-id forward-time, and the spanning-tree vlan vlan-id max-age global configuration commands.
Configuring a Secondary Root Device
When you configure a switch as the secondary root, the switch priority is modified from the default value (32768) to 28672. With this priority, the switch is likely to become the root switch for the specified VLAN if the primary root switch fails. This is assuming that the other network switches use the default switch priority of 32768, and therefore, are unlikely to become the root switch.
You can execute this command on more than one switch to configure multiple backup root switches. Use the same network diameter and hello-time values that you used when you configured the primary root switch with the spanning-tree vlan vlan-id root primary global configuration command.
Beginning in privileged EXEC mode, follow these steps to configure a switch to become a secondary root for the specified VLAN:
DETAILED STEPS
Configuring Port Priority
Beginning in privileged EXEC mode, follow these steps to configure port priority:
DETAILED STEPS
Configuring Path Cost
Beginning in privileged EXEC mode, follow these steps to configure path cost:
DETAILED STEPS
The show spanning-tree interface interface-id privileged EXEC command displays information only for ports that are in a link-up operative state. Otherwise, you can use the show running-config privileged EXEC command to confirm the configuration.
Configuring the Device Priority of a VLAN
You can configure the switch priority and make it more likely that a standalone switch or a switch in the stack will be chosen as the root switch.
This procedure is optional. Beginning in privileged EXEC mode, follow these steps to configure the switch priority of a VLAN:
DETAILED STEPS
Configuring the Hello Time
The hello time is the time interval between configuration messages generated and sent by the root switch.
Beginning in privileged EXEC mode, follow these steps to configure hello time:
DETAILED STEPS
Configuring the Forwarding-Delay Time for a VLAN
Beginning in privileged EXEC mode, follow these steps to configure the forwarding delay time for a VLAN:
DETAILED STEPS
Configuring the Maximum-Aging Time for a VLAN
Beginning in privileged EXEC mode, follow these steps to configure the maximum-aging time for a VLAN:
DETAILED STEPS
Configuring the Transmit Hold-Count
You can configure the BPDU burst size by changing the transmit hold count value.
Beginning in privileged EXEC mode, follow these steps to configure transmit hold-count:
DETAILED STEPS
Monitoring Spanning-Tree Status
To clear spanning-tree counters, use the clear spanning-tree [ interface i nterface-id] privileged EXEC command.
Additional References for Spanning-Tree Protocol
Related Documents
Related Topic | Document Title |
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Spanning tree protocol commands |
LAN Switching Command Reference, Cisco IOS XE Release 3SE (Catalyst 3850 Switches) |
Error Message Decoder
Description | Link |
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To help you research and resolve system error messages in this release, use the Error Message Decoder tool. |
https://www.cisco.com/cgi-bin/Support/Errordecoder/index.cgi |
Standards and RFCs
Standard/RFC | Title |
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None | — |
MIBs
MIB | MIBs Link |
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All supported MIBs for this release. |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
Technical Assistance
Description | Link |
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The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password. |
Feature Information for STP
Release |
Modification |
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Cisco IOS XE 3.2SE |
This feature was introduced. |