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This chapter contains the following sections:
Use the spanning-tree Global Configuration mode command to enable spanning-tree functionality. Use the no form of this command to disable the spanning-tree functionality.
spanning-tree
no spanning-tree
Spanning-tree is enabled.
Global Configuration mode
The following example enables spanning-tree functionality.
switchxxxxxx(config)# spanning-tree
Use the spanning-tree mode Global Configuration mode command to select which Spanning Tree Protocol (STP) protocol to run. Use the no form of this command to restore the default configuration.
spanning-tree mode {stp| rstp | mst | pvst | rapid-pvst}
no spanning-tree mode
stp—Specifies that STP is enabled.
rstp—Specifies that the Rapid STP is enabled.
mst—Specifies that the Multiple STP is enabled.
pvst—Specifies that the PVST+ is enabled.
rapid-pvst—Specifies that the Rapid PVST+ is enabled.
The default is RSTP.
Global Configuration mode
In the RSTP mode, the device uses STP on a port, when the neighbor device uses STP.
In the MSTP mode, the device uses RSTP when the neighbor device uses RSTP, and uses STP when the neighbor device uses STP.
If the PVST mode or the Rapid PVST mode is enabled the switch can support maximum 126 VLANs.
In the Rapid PVST mode, the device uses PVST into a VLAN on a port, when the neighbor device uses PVST.
The following example enables MSTP.
switchxxxxxx(config)# spanning-tree mode mst
Use the spanning-tree forward-time Global Configuration mode command to configure the spanning-tree bridge forward time, which is the amount of time a port remains in the listening and learning states before entering the forwarding state. Use the no form of this command to restore the default configuration.
spanning-tree forward-time seconds
no spanning-tree forward-time
seconds—Specifies the spanning-tree forward time in seconds. (Range: 4–30)
15 seconds.
Global Configuration mode
When configuring the forwarding time, the following relationship should be maintained:
2*(Forward-Time - 1) >= Max-Age
The following example configures the spanning tree bridge forwarding time to 25 seconds.
switchxxxxxx(config)# spanning-tree forward-time 25
Use the spanning-tree hello-time Global Configuration mode command to configure how often the device broadcasts Hello messages to other devices. Use the no form of this command to restore the default configuration.
spanning-tree hello-time seconds
no spanning-tree hello-time
seconds—Specifies the spanning-tree Hello time in seconds. (Range: 1–10)
2 seconds.
Global Configuration mode
When configuring the Hello time, the following relationship should be maintained:
Max-Age >= 2*(Hello-Time + 1)
The following example configures the spanning-tree bridge hello time to 5 seconds.
switchxxxxxx(config)# spanning-tree hello-time 5
Use the spanning-tree max-age Global Configuration mode command to configure the STP maximum age. Use the no form of this command to restore the default configuration.
spanning-tree max-age seconds
no spanning-tree max-age
seconds—Specifies the spanning-tree bridge maximum age in seconds. (Range: 6–40)
The default maximum age is 20 seconds.
Global Configuration mode
When configuring the maximum age, the following relationships should be maintained:
2*(Forward-Time - 1) >= Max-Age
Max-Age >= 2*(Hello-Time + 1)
The following example configures the spanning-tree bridge maximum age to 10 seconds.
switchxxxxxx(config)# spanning-tree max-age 10
Use the spanning-tree priority Global Configuration mode command to configure the device STP priority, which is used to determine which bridge is selected as the root bridge. Use the no form of this command to restore the default device spanning-tree priority.
spanning-tree priority priority
no spanning-tree priority
priority—Specifies the bridge priority. (Range: 0–61440)
Default priority = 32768.
Global Configuration mode
The priority value must be a multiple of 4096.
The switch with the lowest priority is the root of the spanning tree. When more than one switch has the lowest priority, the switch with the lowest MAC address is selected as the root.
The following example configures the spanning-tree priority to 12288.
switchxxxxxx(config)# spanning-tree priority 12288Use the spanning-tree disable Interface (Ethernet, Port Channel) Configuration mode command to disable the spanning tree on a specific port. Use the no form of this command to enable the spanning tree on a port.
spanning-tree disable
no spanning-tree disable
Spanning tree is enabled on all ports.
Interface (Ethernet, Port Channel) Configuration mode
The following example disables the spanning tree on gi1/0/5
switchxxxxxx(config)# interface gi1/0/5
switchxxxxxx(config-if)# spanning-tree disable
Use the spanning-tree cost Interface (Ethernet, Port Channel) Configuration mode command to configure the spanning-tree path cost for a port. Use the no form of this command to restore the default configuration.
spanning-tree cost cost
no spanning-tree cost
cost—Specifies the port path cost. (Range: 1–200000000)
Default path cost is determined by port speed and path cost method (long or short) as shown below.
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Interface |
Long |
Short |
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Port-channel |
Half the default cost based on Port-channel interface speed |
Half the default cost based on Port-channel interface speed |
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TenGigabit Ethernet (10000 Mbps) |
2000 |
2 |
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5 Gigabit Ethernet (5000 Mbps) |
12,000 |
3 |
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2.5 Gigabit Ethernet (2500 Mbps) |
17,000 |
4 |
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Gigabit Ethernet (1000 Mbps) |
20,000 |
4 |
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Fast Ethernet (100 Mbps) |
200,000 |
19 |
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Ethernet (10 Mbps) |
2,000,000 |
100 |
Interface (Ethernet, Port Channel) Configuration mode
The following example configures the spanning-tree cost on gi1/0/15 to 35000.
switchxxxxxx(config)# interface gi1/0/15
switchxxxxxx(config-if)# spanning-tree cost 35000
Use the spanning-tree port-priority Interface (Ethernet, Port Channel) Configuration mode command to configure the port priority. Use the no form of this command to restore the default configuration.
spanning-tree port-priority priority
no spanning-tree port-priority
priority—Specifies the port priority. (Range: 0–240)
The default port priority is 128.
Interface (Ethernet, Port Channel) Configuration mode
The priority value must be a multiple of 16.
The following example configures the spanning priority on gi1/0/15 to 96
switchxxxxxx(config)# interface gi1/0/15
switchxxxxxx(config-if)# spanning-tree port-priority 96
Use the spanning-tree portfast Interface (Ethernet, Port Channel) Configuration mode command to enable the PortFast mode. Use the no form of this command to disable the PortFast mode.
spanning-tree portfast [auto]
no spanning-tree portfast
auto—Specifies delay before putting the interface into the PortFast mode.
PortFast mode is set to auto.
Interface (Ethernet, Port Channel) Configuration mode
In the PortFast mode, the interface is immediately put into the forwarding state upon linkup, without waiting for the standard forward time delay.
Use the spanning-tree portfast command to enable immediately the PortFast mode.
Use the spanning-tree portfast auto to delay the PortFast mode for 3 seconds. The interface will turn into the PortFast mode if for this interval it does not receive a Spanning Tree protocol message.
The following example enables the PortFast mode on gi1/0/15.
switchxxxxxx(config)# interface gi1/0/15
switchxxxxxx(config-if)# spanning-tree portfast
Use the spanning-tree link-type Interface (Ethernet, Port Channel) Configuration mode command to override the default link-type setting determined by the port duplex mode, and enable RSTP transitions to the Forwarding state. Use the no form of this command to restore the default configuration.
spanning-tree link-type {point-to-point | shared}
no spanning-tree spanning-tree link-type
point-to-point—Specifies that the port link type is point-to-point.
shared—Specifies that the port link type is shared.
The device derives the port link type from the duplex mode. A full-duplex port is considered a point-to-point link and a half-duplex port is considered a shared link.
Interface (Ethernet, Port Channel) Configuration mode
The following example enables shared spanning-tree on gi1/0/15.
switchxxxxxx(config)# interface gi1/0/15
switchxxxxxx(config-if)# spanning-tree link-type shared
Use the spanning-tree pathcost method Global Configuration mode command to set the default path cost method. Use the no form of this command to return to the default configuration.
spanning-tree pathcost method {long | short}
no spanning-tree pathcost method
long—Specifies that the default port path costs are within the range: 1–200,000,000.
short—Specifies that the default port path costs are within the range: 1–65,535.
Long path cost method.
Global Configuration mode
This command applies to all the spanning tree instances on the switch.
If the short method is selected, the switch calculates the default cost as 100.
If the long method is selected, the switch calculates the default cost as 20000.
The following example sets the default path cost method to Long.
switchxxxxxx(config)# spanning-tree pathcost method long
Use the spanning-tree bpdu Global Configuration mode command to define Bridge Protocol Data Unit (BPDU) handling when the spanning tree is disabled globally or on a single interface. Use the no form of this command to restore the default configuration.
spanning-tree bpdu {filtering | flooding}
no spanning-tree bpdu
filtering—Specifies that BPDU packets are filtered when the spanning tree is disabled on an interface.
flooding—Specifies that untagged BPDU packets are flooded unconditionally (without applying VLAN rules) to all ports with the spanning tree disabled and BPDU handling mode of flooding. Tagged BPDU packets are filtered.
The default setting is flooding.
Global Configuration mode
The filtering and flooding modes are relevant when the spanning tree is disabled globally or on a single interface.
The following example defines the BPDU packet handling mode as flooding when the spanning tree is disabled on an interface.
switchxxxxxx(config)# spanning-tree bpdu flooding
Use the spanning-tree bpdu Interface (Ethernet, Port Channel) Configuration mode command to define BPDU handling when the spanning tree is disabled on a single interface. Use the no form of this command to restore the default configuration.
spanning-tree bpdu {filtering | flooding}
no spanning-tree bpdu
filtering—Specifies that BPDU packets are filtered when the spanning tree is disabled on an interface.
flooding—Specifies that untagged BPDU packets are flooded unconditionally (without applying VLAN rules) to ports with the spanning tree disabled and BPDU handling mode of flooding. Tagged BPDU packets are filtered.
The spanning-tree bpdu (Global) command determines the default configuration.
Interface (Ethernet, Port Channel) Configuration mode
The following example defines the BPDU packet as flooding when the spanning tree is disabled on gi1/0/3.
switchxxxxxx(config)# interface gi1/0/3
switchxxxxxx(config-if)# spanning-tree bpdu flooding
Use the spanning-tree guard root Interface (Ethernet, Port Channel) Configuration mode command to enable Root Guard on all spanning-tree instances on the interface. Root guard prevents the interface from becoming the root port of the device. Use the no form of this command to disable the root guard on the interface.
spanning-tree guard root
no spanning-tree guard root
Root guard is disabled.
Interface (Ethernet, Port Channel) Configuration mode
Root Guard can be enabled when the device operates in any spanning tree mode.
When Root Guard is enabled, the port changes to the alternate state if the spanning-tree calculations select the port as the root port.
The following example prevents gi1/0/1 from being the root port of the device.
switchxxxxxx(config)# interface gi1/0/1
switchxxxxxx(config-if)# spanning-tree guard root
Use the spanning-tree bpduguard Interface (Ethernet, Port Channel) Configuration mode command to shut down an interface when it receives a Spanning Tree message. Use the no form of this command to restore the default configuration.
spanning-tree bpduguard {enable | disable}
no spanning-tree bpduguard
enable—Enables BPDU Guard.
disable—Disables BPDU Guard.
BPDU Guard is disabled.
Interface (Ethernet, Port Channel) Configuration mode
The command can be enabled when the spanning tree is enabled (useful when the port is in the PortFast mode) or disabled.
The following example shuts down gi1/0/5 when it receives a BPDU.
switchxxxxxx(config)# interface gi1/0/5
switchxxxxxx(config-if)# spanning-tree bpduguard enable
Use the clear spanning-tree counters Privileged EXEC mode command to clear STP counters on all interfaces or on the specified interface
clear spanning-tree counters [interface interface-id]
interface-id— (O'ptional) Specifies an interface ID. The interface ID can be one of the following types: Ethernet port or Port-channel.
All interfaces.
Privileged EXEC mode
The clear spanning-tree counters command clears sent and received STP BPDU counters from the entire switch or from the specified interface
This example shows how to clear STP counter on all interfaces.
switchxxxxxx# clear spanning-tree counters
Use the clear spanning-tree detected-protocols Privileged EXEC mode command to restart the STP migration process (force renegotiation with neighboring switches) on all interfaces or on the specified interface
clear spanning-tree detected-protocols [interface interface-id]
interface-id—Specifies an interface ID. The interface ID can be one of the following types: Ethernet port or Port-channel.
All interfaces.
Privileged EXEC mode
This feature can only be used when working in the RSTP, MSTP, or Rapid PVST mode.
This restarts the STP migration process on all interfaces.
switchxxxxxx# clear spanning-tree detected-protocols
Use the spanning-tree mst priority Global Configuration mode command to configure the device priority for the specified spanning-tree instance. Use the no form of this command to restore the default configuration.
spanning-tree mst instance-id priority priority
no spanning-tree mst instance-id priority
instance-id—Specifies the spanning-tree instance ID. (Range:1– 7 )
priority—Specifies the device priority for the specified spanning-tree instance. This setting determines the likelihood that the switch is selected as the root switch. A lower value increases the probability that the switch is selected as the root switch. (Range: 0–61440)
The default priority is 32768.
Global Configuration mode
The priority value must be a multiple of 4096.
The switch with the lowest priority is the root of the spanning tree.
The following example configures the spanning tree priority of instance 1 to 4096.
switchxxxxxx(config)# spanning-tree mst 1 priority 4096
Use the spanning-tree mst max-hops Global Configuration mode command to configure the number of hops in an MST region before the BDPU is discarded and the port information is aged out. Use the no form of this command to restore the default configuration.
spanning-tree mst max-hops hop-count
no spanning-tree mst max-hops
hop-count—Specifies the number of hops in an MST region before the BDPU is discarded. (Range: 1–40)
The default number of hops is 20.
Global Configuration mode
The following example configures the maximum number of hops that a packet travels in an MST region before it is discarded to 10.
switchxxxxxx(config)# spanning-tree mst max-hops 10
Use the spanning-tree mst port-priority Interface (Ethernet, Port Channel) Configuration mode command to configure the priority of a port. Use the no form of this command to restore the default configuration.
spanning-tree mst instance-id port-priority priority
no spanning-tree mst instance-id port-priority
instance-id—Specifies the spanning tree instance ID. (Range:1– 7 )
priority—Specifies the port priority. (Range: 0–240 in multiples of 16)
The default port priority is 128.
Interface (Ethernet, Port Channel) Configuration mode
The priority value must be a multiple of 16.
The following example configures the port priority of gi1/0/1 to 144.
switchxxxxxx(config)# interface gi1/0/1
switchxxxxxx(config-if)# spanning-tree mst 1 port-priority 144
Use the spanning-tree mst cost Interface (Ethernet, Port Channel) Configuration mode command to configure the path cost for MST calculations. If a loop occurs, the spanning tree considers path cost when selecting an interface to put in the Forwarding state. Use the no form of this command to restore the default configuration.
spanning-tree mst instance-id cost cost
no spanning-tree mst instance-id cost
instance-id—Specifies the spanning-tree instance ID. (Range:1– 7 )
cost—Specifies the port path cost. (Range: 1–200000000)
Default path cost is determined by the port speed and path cost method (long or short) as shown below:
Interface (Ethernet, Port Channel) Configuration mode
The following example configures the MSTP instance 1 path cost for port gi1/0/9 to 4.
switchxxxxxx(config)# interface gi1/0/9
switchxxxxxx(config-if)# spanning-tree mst 1 cost 4
Use the spanning-tree mst configuration Global Configuration mode command to enable configuring an MST region by entering the MST mode.
spanning-tree mst configuration
Global Configuration mode
For two or more switches to be in the same MST region, they must contain the same VLAN mapping, the same configuration revision number, and the same name.
The following example configures an MST region.
switchxxxxxx(config)# spanning-tree mst configuration
switchxxxxxx(config-mst)# instance 1 vlan 10-20
switchxxxxxx(config-mst)# name region1
switchxxxxxx(config-mst)# revision 1
Use instance MST Configuration mode command to map VLANs to an MST instance. Use the no form of this command to restore the default mapping.
instance instance-id vlan vlan-range
no instance instance-id vlan vlan-range
instance-id—MST instance (Range:1– 7)
vlan-range—The specified range of VLANs is added to the existing ones. To specify a range, use a hyphen. To specify a series, use a comma. (Range: 1–4094)
All VLANs are mapped to the common and internal spanning tree (CIST) instance (instance 0).
MST Configuration mode
Before mapping VLANs to an instance, the instance needs to be created using the spanning-tree mst instance command (up to 15 instances can be created).
All VLANs that are not explicitly mapped to an MST instance are mapped to the common and internal spanning tree (CIST) instance (instance 0) and cannot be unmapped from the CIST.
For two or more devices to be in the same MST region, they must have the same VLAN mapping, the same configuration revision number, and the same name.
Example 1. The following example maps VLANs 10-20 to MST instance 1000.
switchxxxxxx(config)# spanning-tree mst instance 1000
switchxxxxxx(config)# spanning-tree mst configuration
switchxxxxxx(config-mst)# instance 1000 vlan 10-20
Example 2. In the following example the attempt to map VLANs to MST instance ID 1001 fails, since instance ID 1001 was not created by user:
switchxxxxxx(config)# spanning-tree mst configuration
switchxxxxxx(config-mst)# instance 1000 vlan 30-40
Cannot map VLANs to instance 1001. Instance 1001 does not exist.Use the name MST Configuration mode command to define the MST region name. Use the no form of this command to restore the default setting.
name string
no name
string—Specifies the MST region name. (Length: 1–32 characters)
The default name is the bridge MAC address.
MST Configuration mode
The following example defines the region name as Region1.
switchxxxxxx(config)# spanning-tree mst configuration
switchxxxxxx(config-mst)# name region1
Use the revision MST Configuration mode command to define the MST configuration revision number. Use the no form of this command to restore the default configuration.
revision value
no revision
value—Specifies the MST configuration revision number. (Range: 0–65535)
The default configuration revision number is 0.
MST Configuration mode
The following example sets the configuration revision to 1.
switchxxxxxx(config)# spanning-tree mst configuration
switchxxxxxx(config-mst) # revision 1
Use the show MST Configuration mode command to display the current or pending MST region configuration.
show {current | pending}
current—Displays the current MST region configuration.
pending—Displays the pending MST region configuration.
MST Configuration mode
The following example displays a pending MST region configuration
switchxxxxxx(config-mst)# show pending
Gathering information ..........
Current MST configuration
Name: Region1
Revision: 1
Digest: 0xB41829F9030A054FB74EF7A8587FF58D
Instance VLANs Mapped State
-------- ------------------------ -----
0 1-4094 Disabled
switchxxxxxx(config-mst)#
Use the exit MST Configuration mode command to exit the MST region Configuration mode and apply all configuration changes.
exit
MST Configuration mode
The following example exits the MST Configuration mode and saves changes.
switchxxxxxx(config)# spanning-tree mst configuration
switchxxxxxx(config-mst)# exit
switchxxxxxx(config)#
Use the abort MST Configuration mode command to exit the MST Configuration mode without applying the configuration changes.
abort
MST Configuration mode
The following example exits the MST Configuration mode without saving changes.
switchxxxxxx(config)# spanning-tree mst configuration
switchxxxxxx(config-mst)# abort
Use the spanning-tree mst instance Global Configuration mode command to create an MST instance to which VLANs can be mapped. To delete an instance use the no form of command.
spanning-tree mst instance instance-id
no spanning-tree mst instance instance-id
instance-id—Specifies the spanning-tree instance ID. (range 1-4094)
Instance IDs 1-4094 do not exist.
Global Configuration mode
Use the spanning-tree mst instance command to create an MST instance. Up to 15 can be created. Instance 0 (the common and internal spanning tree (CIST) instance) exists by default on device and cannot be removed.
Creating an MST instance allows to map VLANs to this instance in MST Configuration mode) and to configure the following settings on the created instance:
Configure instance priority - command spanning-tree mst priority.
Configure port priority per instance - command spanning-tree mst port-priority
Configure port cost per instance - command spanning-tree mst cost
Use the no form of command to delete an instance. An instance cannot be deleted if one or more VLANs are still mapped to it. Deleting an instance removes all STP configuration related to that instance.
Example 1. The following example creates an MST instance with instance ID of 248:
switchxxxxxx(config)#spanning-tree mst instance 248Example 2:The following example removes MST instance 248 from device.
switchxxxxxx(config)# no spanning-tree mst instance 248Example 3:In the following example removal of instance ID 365 fails because VLANs are still mapped to this instance:
switchxxxxxx(config)# no spanning-tree mst instance 365
Cannot delete instance 365. One or more VLANs are mapped to this instance.Use the show spanning-tree Privileged EXEC mode command to display the spanning-tree configuration.
show spanning-tree [interface-id] [{instance instance-id} | {vlan vlan-id}]
show spanning-tree [detail] [active | blockedports] [{instance instance-id} | {vlan vlan-id}]
show spanning-tree inconsistentports
show spanning-tree mst-configuration
show spanning-tree mst-configuration digest
interface-id—Specifies an interface ID (optional). The interface ID can be one of the following types: Ethernet port or Port-channel.
detail—Displays detailed information.
active—Displays active ports only. Active ports are ports that are STP enabled and in the operational status of up. If device mode is PVST+ or Rapid PVST+ - ports also need to be members of the displayed VLAN.
blockedports—Displays blocked ports only.
instance-id—MST instance (Range:1– 7). The parameter could be defined only when mode MSTP is enabled.
vlan vlan-id—Specifies the VLAN ID. (Range: 1–4094). The parameter could be defined only when mode PVST or RPVST is enabled.
inconsistentports - Displays the ports that are in an inconsistent STP state. Command is relevant only when in PVST+ or Rapid PVST mode.
mst-configuration—Displays the MST configuration information.
mst-configuration digest—Displays the MST configuration digest information.
If no interface is specified, the default is all interfaces.
Privileged EXEC mode
This command only works when MST is enabled.
The following examples display spanning-tree information in various configurations:
Display examples for a device that is in STP or RSTP mode -
switchxxxxxx# show spanning-tree
Spanning tree enabled mode RSTP
Default port cost method: long
Loopback guard: Disabled
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switchxxxxxx# show spanning-tree
Spanning tree disabled (BPDU filtering) mode RSTP
Default port cost method: long
Loopback guard: Disabled
Interfaces
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switchxxxxxx# show spanning-tree
Spanning tree disabled (BPDU filtering) mode RSTP
Default port cost method: long
Loopback guard: Disabled
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Forward Delay 15 sec |
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switchxxxxxx# show spanning-tree active
Spanning tree enabled mode RSTP
Default port cost method: long
Loopback guard: Disabled
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Max Age 20 sec |
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switchxxxxxx# show spanning-tree blockedports
Spanning tree enabled mode RSTP
Default port cost method: long
Loopback guard: Disabled
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switchxxxxxx# show spanning-tree detail
Spanning tree enabled mode RSTP
Default port cost method: long
Loopback guard: Disabled
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Number of transitions to forwarding state: N/A
BPDU: sent N/A, received N/A
switchxxxxxx# show spanning-tree ethernet gi1/0/1
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Number of transitions to forwarding state: 1
BPDU: sent 2, received 120638
Display examples for a device that is in PVST or Rapid PVST mode-
switchxxxxxx# show spanning-tree
Spanning tree enabled mode Rapid-PVST
Default port cost method: long
Loopback guard: Disabled
VLAN 1
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Max Age 20 sec |
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* Port Type or PVID Inconsistency
VLAN 20
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Max Age 20 sec |
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* Port Type or PVID Inconsistency
switchxxxxxx# show spanning-tree active
Spanning tree enabled mode Rapid-PVST
Default port cost method: long
Loopback guard: Disabled
VLAN 1
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Max Age 20 sec |
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* Port Type or PVID Inconsistency
VLAN 20
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Max Age 20 sec |
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* Port Type or PVID Inconsistency
switchxxxxxx# show spanning-tree VLAN 20
Spanning tree enabled mode PVST
Default port cost method: long
Loopback guard: Disabled
VLAN 20
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* Port Type or PVID Inconsistency
switchxxxxxx# show spanning-tree gi1/0/2
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* Port Type or PVID Inconsistency
switchxxxxxx# show spanning-tree gi1/0/2 vlan 3
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switchxxxxxx# show spanning-tree inconsistentports
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Number of inconsistent ports (segments) in the system : 4
Display examples for a device that is in MSTP mode -
switchxxxxxx# show spanning-tree mst-configuration
Name: Region1
Revision: 1
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switchxxxxxx# show spanning-tree mst-configuration digest
Name: Region1
Revision: 1
Format selector: 0
Digest: 0xB41829F9030A054FB74EF7A8587FF58D
Number of instances configured: 3
switchxxxxxx# show spanning-tree
Spanning tree enabled mode MSTP
Default port cost method: long
Loopback guard: Disabled
###### MST 0 Vlans Mapped: 1-9
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Interfaces
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###### MST 1 Vlans Mapped: 10-20
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Interfaces
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switchxxxxxx# show spanning-tree detail
Spanning tree enabled mode MSTP
Default port cost method: long
Loopback guard: Disabled
###### MST 0 Vlans Mapped: 1-9
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###### MST 1 Vlans Mapped: 10-20
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Use the show spanning-tree bpdu User EXEC mode command to display the BPDU handling when spanning-tree is disabled.
show spanning-tree bpdu [interface-id | detailed]
interface-id—Specifies an interface ID. The interface ID can be one of the following types: Ethernet port or Port-channel.
detailed—Displays information for non-present ports in addition to present ports.
Show information for all interfaces. If detailed is not used, only present ports are displayed.
User EXEC mode
The following examples display spanning-tree BPDU information:
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Use the spanning-tree loopback-guard global configuration command to shut down an interface if it receives a loopback BPDU. Use the no form of this command to return the default setting.
spanning-tree loopback-guard
no spanning-tree loopback-guard
Global
This enables shutting down all interfaces if a loopback BPDU is received on it.
switchxxxxxx(config)# spanning-tree loopback-guard
To configure the spanning-tree bridge forward time for a VLAN, use the spanning-tree vlan forward-time command in Global Configuration mode. To return to the default settings, use the no form of this command.
spanning-tree vlan vlan-range forward-time seconds
no spanning-tree vlan vlan-range forward-time
vlan-range—Specifies a range of VLANs to configure. To specify a range, use a hyphen. To specify a series, use a comma. (Range: 2–4094)
seconds—Specifies the spanning-tree forward time in seconds. (Range: 4–30)
The default forward time is 15 seconds.
Global Configuration mode
The spanning-tree bridge forward time is the amount of time a port remains in the listening and learning states before entering the forwarding state.
When configuring the forwarding time, the following relationship should be maintained:
2*(Forward-Time - 1) >= Max-Age
Use this command to configure the forward time for the specified VLAN instance. Setting will take effect if Spanning-tree mode is set to PVST or Rapid PVST .
The following example configures the spanning tree bridge forwarding time to 25 seconds for VLAN 100:
switchxxxxxx(config)# spanning-tree vlan 100 forward-time 25
To configure the spanning-tree bridge hello time for a VLAN, use the spanning-tree vlan hello-time command in Global Configuration mode. To return to the default settings, use the no form of this command.
spanning-tree vlan vlan-range hello-time seconds
no spanning-tree vlan vlan-range hello-time
vlan-range—Specifies a range of VLANs to configure. To specify a range, use a hyphen. To specify a series, use a comma. (Range: 2–4094)
seconds—Specifies the spanning-tree Hello time in seconds. (Range: 1–10)
The default hello time is 2 seconds.
Global Configuration mode
The spanning-tree bridge hello time is the time between two sequential sent Hello messages.
When configuring the Hello time, the following relationship should be maintained:
Max-Age >= 2*(Hello-Time + 1)
Use this command to configure the hello time for the specified VLAN instance. Setting will take effect if Spanning-tree mode is set to PVST or Rapid PVST .
The following example configures the spanning-tree bridge hello time to 5 seconds for VLANs 100-101:
switchxxxxxx(config)# spanning-tree vlan 100-101 hello-time 5
To configure the spanning-tree bridge maximum age time for a VLAN, use the spanning-tree vlan max-age command in Global Configuration mode. To return to the default settings, use the no form of this command.
spanning-tree vlan vlan-range max-age seconds
no spanning-tree vlan vlan-range max-age
vlan-range—Specifies a range of VLANs to configure. To specify a range, use a hyphen. To specify a series, use a comma. (Range: 2–4094)
seconds—Specifies the spanning-tree bridge maximum age in seconds. (Range: 6–40)
The default max-age value is 15 seconds.
Global Configuration mode
When configuring the maximum age, the following relationships should be maintained:
2*(Forward-Time - 1) >= Max-Age
Max-Age >= 2*(Hello-Time + 1)
Use this command to configure the maximum age for the specified VLAN instance. Setting will take effect if Spanning-tree mode is set to PVST or Rapid PVST .
The following example configures the spanning-tree bridge maximum age to 10 seconds for VLAN 100:
switchxxxxxx(config)# spanning-tree vlan 100 max-age 10
To configure the spanning-tree bridge priority for a VLAN, use the spanning-tree vlan priority command in Global Configuration mode. To return to the default settings, use the no form of this command.
spanning-tree vlan vlan-range priority priority
no spanning-tree vlan vlan-range priority
vlan-range—Specifies a range of VLANs to configure. To specify a range, use a hyphen. To specify a series, use a comma. (Range: 2–4094)
priority—Specifies the bridge priority. (Range: 0–61440)
The default priority equal to 32768.
Global Configuration mode
The priority value must be a multiple of 4096.
The switch with the lowest priority is the root of the spanning tree. When more than one switch has the lowest priority, the switch with the lowest MAC address is selected as the root.
Use this command to configure the bridge priority for the specified VLAN instance. Setting will take effect if Spanning-tree mode is set to PVST or Rapid PVST .
The following example configures the spanning-tree priority to 12288 for VLAN 100-105:
switchxxxxxx(config)# spanning-tree vlan 100-105 priority 12288
To configure the spanning-tree bridge path cost for a port and a VLAN, use the spanning-tree vlan cost command in Interface (Ethernet, Port Channel) Configuration mode. To return to the default settings, use the no form of this command.
spanning-tree vlan vlan-range cost cost
no spanning-tree vlan vlan-range cost
vlan-range—Specifies a range of VLANs to configure. To specify a range, use a hyphen. To specify a series, use a comma. (Range: 2–4094)
cost—Specifies the port path cost. (Range: 1–200000000)
Default path cost is determined by port speed and path cost method (long or short).
Interface (Ethernet, Port Channel) Configuration mode
Use this command to configure the port cost for the specified VLAN instance. Setting will take effect if Spanning-tree mode is set to PVST or Rapid PVST .
The VLAN instances that can be specified are VLAN ID 2-4094.
The following example configures the spanning-tree cost to 35000 for port gi1/0/15 and VLAN 100:
switchxxxxxx(config)# interface gi1/0/15
switchxxxxxx(config-if)# spanning-tree vlan 100 cost 35000
To configure the spanning-tree port priority for a VLAN, use the spanning-tree vlan port-priority command in Interface (Ethernet, Port Channel) Configuration mode. To return to the default settings, use the no form of this command.
spanning-tree vlan vlan-range port-priority priority
no spanning-tree vlan vlan-range port-priority
vlan-range—Specifies a range of VLANs to configure. To specify a range, use a hyphen. To specify a series, use a comma. (Range: 2–4094)
priority—Specifies the port priority. (Range: 0–240)
The default port priority is 128.
Interface (Ethernet, Port Channel) Configuration mode
The priority value must be a multiple of 16.
Use this command to configure the port priority for the specified VLAN instance. Setting will take effect if Spanning-tree mode is set to PVST or Rapid PVST .
The following example configures the spanning priority on gi1/0/15 to 16 for VLANs 100-102:
switchxxxxxx(config)# interface gi1/0/15-16
switchxxxxxx(config-if)# spanning-tree vlan 100-102 port-priority 96
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