Catalyst 3750 Command Reference, Release 12.2(55)SE

 

Syntax Description

This command has no arguments or keywords.

 

Defaults

The port is enabled (not shut down).

 

Command History

 

Usage Guidelines

The shutdown command causes a port to stop forwarding. You can enable the port with the no shutdown command.

The no shutdown command has no effect if the port is a static-access port assigned to a VLAN that has been deleted, suspended, or shut down. The port must first be a member of an active VLAN before it can be re-enabled.

The shutdown command disables all functions on the specified interface.

This command also marks the interface as unavailable. To see if an interface is disabled, use the show interfaces privileged EXEC command. An interface that has been shut down is shown as administratively down in the display.

Examples

These examples show how to disable and re-enable a port:

You can verify your settings by entering the show interfaces privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

No default is defined.

 

Command History

 

Usage Guidelines

The shutdown vlan command does not change the VLAN information in the VTP database. The command shuts down local traffic, but the switch still advertises VTP information.

Examples

This example shows how to shut down traffic on VLAN 2:

You can verify your setting by entering the show vlan privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

This feature is disabled.

 

Command History

 

Usage Guidelines

This command enables the rate (threshold) for a port to be error disabled when it receives small frames. Small frames are considered packets that are 67 frames or less.

Use the errdisable detect cause small-frame global configuration command to globally enable the small-frames threshold for each port.

You can configure the port to be automatically re-enabled by using the errdisable recovery cause small-frame global configuration command. You configure the recovery time by using the errdisable recovery interval interval global configuration command.

Examples

This example shows how to enable the small-frame arrival rate feature so that the port is error disabled if incoming small frames arrived at 10,000 pps.

You can verify your setting by entering the show interfaces privileged EXEC command.

 

Related Commands

 

Syntax Description

Note The snmp-server enable informs global configuration command is not supported. To enable the sending of SNMP inform notifications, use the snmp-server enable traps global configuration command combined with the snmp-server host host-addr informs global configuration command.

 

Defaults

The sending of SNMP traps is disabled.

 

Command History

 

Usage Guidelines

Specify the host (NMS) that receives the traps by using the snmp-server host global configuration command. If no trap types are specified, all types are sent.

When supported, use the snmp-server enable traps command to enable sending of traps or informs.

Note Informs are not supported in SNMPv1.

To enable more than one type of trap, you must enter a separate snmp-server enable traps command for each trap type.

To set the CPU threshold notification types and values, use the process cpu threshold type global configuration command.

Examples

This example shows how to send VTP traps to the NMS:

You can verify your setting by entering the show vtp status or the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

This command is disabled by default. No notifications are sent.

If you enter this command with no keywords, the default is to send all trap types to the host. No informs are sent to this host.

If no version keyword is present, the default is Version 1.

If Version 3 is selected and no authentication keyword is entered, the default is the noauth (noAuthNoPriv) security level.

 

Command History

 

Usage Guidelines

SNMP notifications can be sent as traps or inform requests. Traps are unreliable because the receiver does not send acknowledgments when it receives traps. The sender cannot determine if the traps were received. However, an SNMP entity that receives an inform request acknowledges the message with an SNMP response PDU. If the sender never receives the response, the inform request can be sent again. Thus, informs are more likely to reach their intended destinations.

However, informs consume more resources in the agent and in the network. Unlike a trap, which is discarded as soon as it is sent, an inform request must be held in memory until a response is received or the request times out. Traps are also sent only once, but an inform might be retried several times. The retries increase traffic and contribute to a higher overhead on the network.

If you do not enter an snmp-server host command, no notifications are sent. To configure the switch to send SNMP notifications, you must enter at least one snmp-server host command. If you enter the command with no keywords, all trap types are enabled for the host. To enable multiple hosts, you must enter a separate snmp-server host command for each host. You can specify multiple notification types in the command for each host.

If a local user is not associated with a remote host, the switch does not send informs for the auth (authNoPriv) and the priv (authPriv) authentication levels.

When multiple snmp-server host commands are given for the same host and kind of notification (trap or inform), each succeeding command overwrites the previous command. Only the last snmp-server host command is in effect. For example, if you enter an snmp-server host inform command for a host and then enter another snmp-server host inform command for the same host, the second command replaces the first.

The snmp-server host command is used with the snmp-server enable traps global configuration command. Use the snmp-server enable traps command to specify which SNMP notifications are sent globally. For a host to receive most notifications, at least one snmp-server enable traps command and the snmp-server host command for that host must be enabled. Some notification types cannot be controlled with the snmp-server enable traps command. For example, some notification types are always enabled. Other notification types are enabled by a different command.

The no snmp-server host command with no keywords disables traps, but not informs, to the host. To disable informs, use the no snmp-server host informs command.

Examples

This example shows how to configure a unique SNMP community string named comaccess for traps and prevent SNMP polling access with this string through access-list 10:

This example shows how to send the SNMP traps to the host specified by the name myhost.cisco.com. The community string is defined as comaccess :

This example shows how to enable the switch to send all traps to the host myhost.cisco.com by using the community string public :

You can verify your settings by entering the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

By default, the traps for both address addition and address removal are disabled.

 

Command History

 

Usage Guidelines

Even though you enable the notification trap for a specific interface by using the snmp trap mac-notification change command, the trap is generated only when you enter the snmp-server enable traps mac-notification change and the mac address-table notification change global configuration commands.

Examples

This example shows how to enable the MAC notification trap when a MAC address is added to a port:

You can verify your settings by entering the show mac address-table notification change interface privileged EXEC command.

 

Related Commands

 

Syntax Description

This command has no arguments or keywords.

 

Defaults

BackboneFast is disabled.

 

Command History

 

Usage Guidelines

You can configure the BackboneFast feature for rapid PVST+ or for multiple spanning-tree (MST) mode, but the feature remains disabled (inactive) until you change the spanning-tree mode to PVST+.

BackboneFast starts when a root port or blocked port on a switch receives inferior BPDUs from its designated switch. An inferior BPDU identifies a switch that declares itself as both the root bridge and the designated switch. When a switch receives an inferior BPDU, it means that a link to which the switch is not directly connected (an indirect link) has failed (that is, the designated switch has lost its connection to the root switch. If there are alternate paths to the root switch, BackboneFast causes the maximum aging time on the interfaces on which it received the inferior BPDU to expire and allows a blocked port to move immediately to the listening state. BackboneFast then transitions the interface to the forwarding state. For more information, see the software configuration guide for this release.

Enable BackboneFast on all supported switches to allow the detection of indirect link failures and to start the spanning-tree reconfiguration sooner.

Examples

This example shows how to enable BackboneFast on the switch:

You can verify your setting by entering the show spanning-tree summary privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

BPDU filtering is disabled.

 

Command History

 

Usage Guidelines

You can enable the BPDU filtering feature when the switch is operating in the per-VLAN spanning-tree plus (PVST+), rapid-PVST+, or the multiple spanning-tree (MST) mode.

Caution Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in spanning-tree loops.

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You can globally enable BPDU filtering on all Port Fast-enabled interfaces by using the spanning-tree portfast bpdufilter default global configuration command.

You can use the spanning-tree bpdufilter interface configuration command to override the setting of the spanning-tree portfast bpdufilter default global configuration command.

Examples

This example shows how to enable the BPDU filtering feature on a port:

You can verify your setting by entering the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

BPDU guard is disabled.

 

Command History

 

Usage Guidelines

The BPDU guard feature provides a secure response to invalid configurations because you must manually put the interface back in service. Use the BPDU guard feature in a service-provider network to prevent an interface from being included in the spanning-tree topology.

You can enable the BPDU guard feature when the switch is operating in the per-VLAN spanning-tree plus (PVST+), rapid-PVST+, or the multiple spanning-tree (MST) mode.

You can globally enable BPDU guard on all Port Fast-enabled interfaces by using the spanning-tree portfast bpduguard default global configuration command.

You can use the spanning-tree bpduguard interface configuration command to override the setting of the spanning-tree portfast bpduguard default global configuration command.

Examples

This example shows how to enable the BPDU guard feature on a port:

You can verify your setting by entering the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default path cost is computed from the interface bandwidth setting. These are the IEEE default path cost values:

• 1000 Mb/s—4
• 100 Mb/s—19
• 10 Mb/s—100

 

Command History

 

Usage Guidelines

When you configure the cost, higher values represent higher costs.

If you configure an interface with both the spanning-tree vlan vlan-id cost cost command and the spanning-tree cost cost command, the spanning-tree vlan vlan-id cost cost command takes effect.

Examples

This example shows how to set the path cost to 250 on a port:

This example shows how to set a path cost to 300 for VLANs 10, 12 to 15, and 20:

You can verify your settings by entering the show spanning-tree interface interface-id privileged EXEC command.

 

Related Commands

 

Syntax Description

This command has no arguments or keywords.

 

Defaults

EtherChannel guard is enabled on the switch.

 

Command History

 

Usage Guidelines

When the switch detects an EtherChannel misconfiguration, this error message appears:

To show switch ports that are in the misconfigured EtherChannel, use the show interfaces status err-disabled privileged EXEC command. To verify the EtherChannel configuration on a remote device, use the show etherchannel summary privileged EXEC command on the remote device.

When a port is in the error-disabled state because of an EtherChannel misconfiguration, you can bring it out of this state by entering the errdisable recovery cause channel-misconfig global configuration command, or you can manually re-enable it by entering the shutdown and no shut down interface configuration commands.

Examples

This example shows how to enable the EtherChannel guard misconfiguration feature:

You can verify your settings by entering the show spanning-tree summary privileged EXEC command.

 

Related Commands

 

Syntax Description

This command has no arguments or keywords.

 

Defaults

The extended system ID is enabled.

 

Command History

 

Usage Guidelines

The switch supports the IEEE 802.1t spanning-tree extensions. Some of the bits previously used for the switch priority are now used for the extended system ID (VLAN identifier for the per-VLAN spanning-tree plus [PVST+] and rapid PVST+ or as an instance identifier for the multiple spanning tree [MST]).

The 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 or multiple spanning-tree instance. 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 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 more information, see the “spanning-tree mst root” and the “spanning-tree vlan” sections.

If your network consists of switches that do not support the extended system ID and switches that do support it, 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.

 

Related Commands

 

Syntax Description

 

Defaults

Root guard is disabled.

Loop guard is configured according to the spanning-tree loopguard default global configuration command (globally disabled).

 

Command History

 

Usage Guidelines

You can enable root guard or loop guard when the switch is operating in the per-VLAN spanning-tree plus (PVST+), rapid-PVST+, or the multiple spanning-tree (MST) mode.

When root guard is enabled, if spanning-tree calculations cause an interface to be selected as the root port, the interface transitions to the root-inconsistent (blocked) state to prevent the customer’s switch from becoming the root switch or being in the path to the root. The root port provides the best path from the switch to the root switch.

When the no spanning-tree guard or the no spanning-tree guard none command is entered, root guard is disabled for all VLANs on the selected interface. If this interface is in the root-inconsistent (blocked) state, it automatically transitions to the listening state.

Do not enable root guard on interfaces that will be used by the UplinkFast feature. With UplinkFast, the backup interfaces (in the blocked state) replace the root port in the case of a failure. However, if root guard is also enabled, all the backup interfaces used by the UplinkFast feature are placed in the root-inconsistent state (blocked) and prevented from reaching the forwarding state. The UplinkFast feature is not available when the switch is operating in the rapid-PVST+ or MST mode.

Loop guard is most effective when it is configured on the entire switched network. When the switch is operating in PVST+ or rapid-PVST+ mode, loop guard prevents alternate and root ports from becoming designated ports, and spanning tree does not send bridge protocol data units (BPDUs) on root or alternate ports. When the switch is operating in MST mode, BPDUs are not sent on nonboundary interfaces if the interface is blocked by loop guard in all MST instances. On a boundary interface, loop guard blocks the interface in all MST instances.

To disable root guard or loop guard, use the spanning-tree guard none interface configuration command. You cannot enable both root guard and loop guard at the same time.

You can override the setting of the spanning-tree loopguard default global configuration command by using the spanning-tree guard loop interface configuration command.

Examples

This example shows how to enable root guard on all the VLANs associated with the specified port:

This example shows how to enable loop guard on all the VLANs associated with the specified port:

You can verify your settings by entering the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The switch derives the link type of an interface from the duplex mode. A full-duplex interface is considered a point-to-point link, and a half-duplex interface is considered a shared link.

 

Command History

 

Usage Guidelines

You can override the default setting of the link type by using the spanning-tree link-type command. For example, a half-duplex link can be physically connected point-to-point to a single interface on a remote switch running the Multiple Spanning Tree Protocol (MSTP) or the rapid per-VLAN spanning-tree plus (rapid-PVST+) protocol and be enabled for rapid transitions.

Examples

This example shows how to specify the link type as shared (regardless of the duplex setting) and to prevent rapid transitions to the forwarding state:

You can verify your setting by entering the show spanning-tree mst interface interface-id or the show spanning-tree interface interface-id privileged EXEC command.

 

Related Commands

 

Syntax Description

This command has no arguments or keywords.

 

Defaults

Loop guard is disabled.

 

Command History

 

Usage Guidelines

You can enable the loop guard feature when the switch is operating in the per-VLAN spanning-tree plus (PVST+), rapid-PVST+, or the multiple spanning-tree (MST) mode.

Loop guard is most effective when it is configured on the entire switched network. When the switch is operating in PVST+ or rapid-PVST+ mode, loop guard prevents alternate and root ports from becoming designated ports, and spanning tree does not send bridge protocol data units (BPDUs) on root or alternate ports. When the switch is operating in MST mode, BPDUs are not sent on nonboundary interfaces if the interface is blocked by loop guard in all MST instances. On a boundary interface, loop guard blocks the interface in all MST instances.

Loop guard operates only on interfaces that the spanning tree identifies as point-to-point.

You can override the setting of the spanning-tree loopguard default global configuration command by using the spanning-tree guard loop interface configuration command.

Examples

This example shows how to globally enable loop guard:

You can verify your settings by entering the show running-config privileged EXEC comm and.

 

Related Commands

 

Syntax Description

 

Defaults

The default mode is PVST+.

 

Command History

 

Usage Guidelines

The switch supports PVST+, rapid PVST+, and MSTP, but only one version can be active at any time: All VLANs run PVST+, all VLANs run rapid PVST+, or all VLANs run MSTP. All stack members run the same version of spanning-tree.

When you enable the MST mode, RSTP is automatically enabled.

Caution Changing spanning-tree modes can disrupt traffic because all spanning-tree instances are stopped for the previous mode and restarted in the new mode.

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Examples

This example shows to enable MST and RSTP on the switch:

This example shows to enable rapid PVST+ on the switch:

You can verify your setting by entering the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

This command has no arguments or keywords.

 

Defaults

The default mapping is that all VLANs are mapped to the common and internal spanning-tree (CIST) instance (instance 0).

The default name is an empty string.

The revision number is 0.

 

Command History

 

Usage Guidelines

The spanning-tree mst configuration command enables the MST configuration mode. These configuration commands are available:

• abort : exits the MST region configuration mode without applying configuration changes.
• exit : exits the MST region configuration mode and applies all configuration changes.
• instance instance-id vlan vlan-range : maps VLANs to an MST instance. The range for the instance-id is 1 to 4094. The range for vlan-range is 1 to 4094. You can specify a single VLAN identified by VLAN ID number, a range of VLANs separated by a hyphen, or a series of VLANs separated by a comma.
• name name : sets the configuration name. The name string has a maximum length of 32 characters and is case sensitive.
• no : negates the instance, name, and revision commands or sets them to their defaults.
• private-vlan : Though visible in the command-line help strings, this command is not supported.
• revision version : sets the configuration revision number. The range is 0 to 65535.
• show [ current | pending ] : displays the current or pending MST region configuration.

In MST mode, the switch stack supports up to 65 MST instances. The number of VLANs that can be mapped to a particular MST instance is unlimited.

When you map VLANs to an MST instance, the mapping is incremental, and VLANs specified in the command are added to or removed from the VLANs that were previously mapped. To specify a range, use a hyphen; for example, instance 1 vlan 1-63 maps VLANs 1 to 63 to MST instance 1. To specify a series, use a comma; for example, instance 1 vlan 10, 20, 30 maps VLANs 10, 20, and 30 to MST instance 1.

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 by using the no form of the command.

For two or more switches to be in the same MST region, they must have the same VLAN mapping, the same configuration revision number, and the same name.

Examples

This example shows how to enter MST configuration mode, map VLANs 10 to 20 to MST instance 1, name the region region1, set the configuration revision to 1, display the pending configuration, apply the changes, and return to global configuration mode:

This example shows how to add VLANs 1 to 100 to the ones already mapped (if any) to instance 2, to move VLANs 40 to 60 that were previously mapped to instance 2 to the CIST instance, to add VLAN 10 to instance 10, and to remove all the VLANs mapped to instance 2 and map them to the CIST instance:

You can verify your settings by entering the show pending MST configuration command.

 

Related Commands

 

Syntax Description

 

Defaults

The default path cost is computed from the interface bandwidth setting. These are the IEEE default path cost values:

• 1000 Mb/s—20000
• 100 Mb/s—200000
• 10 Mb/s—2000000

 

Command History

 

Usage Guidelines

When you configure the cost, higher values represent higher costs.

Examples

This example shows how to set a path cost of 250 on a port associated with instances 2 and 4:

You can verify your settings by entering the show spanning-tree mst interface interface-id privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 15 seconds.

 

Command History

 

Usage Guidelines

Changing the spanning-tree mst forward-time command affects all spanning-tree instances.

Examples

This example shows how to set the spanning-tree forwarding time to 18 seconds for all MST instances:

You can verify your setting by entering the show spanning-tree mst privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 2 seconds.

 

Command History

 

Usage Guidelines

After you set the spanning-tree mst max-age seconds global configuration command, if a switch does not receive BPDUs from the root switch within the specified interval, the switch recomputes the spanning-tree topology. The max-age setting must be greater than the hello-time setting.

Changing the spanning-tree mst hello-time command affects all spanning-tree instances.

Examples

This example shows how to set the spanning-tree hello time to 3 seconds for all multiple spanning-tree (MST) instances:

You can verify your setting by entering the show spanning-tree mst privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 20 seconds.

 

Command History

 

Usage Guidelines

After you set the spanning-tree mst max-age seconds global configuration command, if a switch does not receive BPDUs from the root switch within the specified interval, the switch recomputes the spanning-tree topology. The max-age setting must be greater than the hello-time setting.

Changing the spanning-tree mst max-age command affects all spanning-tree instances.

Examples

This example shows how to set the spanning-tree max-age to 30 seconds for all multiple spanning-tree (MST) instances:

You can verify your setting by entering the show spanning-tree mst privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 20 hops.

 

Command History

 

Usage Guidelines

The root switch of the instance always sends a BPDU (or M-record) with a cost of 0 and the hop count set to the maximum value. When a switch receives this BPDU, it decrements the received remaining hop count by one and propagates the decremented count as the remaining hop count in the generated M-records. A switch discards the BPDU and ages the information held for the interface when the count reaches 0.

Changing the spanning-tree mst max-hops command affects all spanning-tree instances.

Examples

This example shows how to set the spanning-tree max-hops to 10 for all multiple spanning-tree (MST) instances:

You can verify your setting by entering the show spanning-tree mst privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 128.

 

Command History

 

Usage Guidelines

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, the multiple spanning tree (MST) puts the interface with the lowest interface number in the forwarding state and blocks other interfaces.

If your switch is a member of a switch stack, you must use the spanning-tree mst [ instance-id ] cost cost interface configuration command instead of the spanning-tree mst [ instance vlan-id ] port-priority priority interface configuration command to select an interface to put in the forwarding state. Assign lower cost values to interfaces that you want selected first and higher cost values to interfaces that you want selected last.

Examples

This example shows how to increase the likelihood that the interface associated with spanning-tree instances 20 and 22 is placed into the forwarding state if a loop occurs:

You can verify your settings by entering the show spanning-tree mst interface interface-id privileged EXEC command.

 

Related Commands

 

Syntax Description

This command has no arguments or keywords.

 

Command Default

The default state is automatic detection of prestandard neighbors.

 

Command History

 

Usage Guidelines

The port can accept both prestandard and standard BPDUs. If the neighbor types are mismatched, only the common and internal spanning tree (CIST) runs on this interface.

Note If a switch port is connected to a switch running prestandard Cisco IOS software, you must use the spanning-tree mst pre-standard interface configuration command on the port. If you do not configure the port to send only prestandard BPDUs, the Multiple STP (MSTP) performance might diminish.

When the port is configured to automatically detect prestandard neighbors, the prestandard flag always appears in the show spanning-tree mst commands.

Examples

This example shows how to configure a port to send only prestandard BPDUs:

You can verify your settings by entering the show spanning-tree mst privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 32768.

 

Command History

Examples

This example shows how to set the spanning-tree priority to 8192 for multiple spanning-tree instances (MST) 20 to 21:

You can verify your settings by entering the show spanning-tree mst instance-id privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The primary root switch priority is 24576.

The secondary root switch priority is 28672.

The hello time is 2 seconds.

 

Command History

 

Usage Guidelines

Use the spanning-tree mst instance-id root command only on backbone switches.

Whe n you enter the spanning-tree mst instance-id root command, the software tries to set a high enough priority to make this switch the root of the spanning-tree instance. Because of the extended system ID support, the switch sets the switch priority for the instance to 24576 if this value will cause this switch to become the root for the specified instance. If any root switch for the specified instance has a switch priority lower than 24576, the switch sets its own priority to 4096 less than the lowest switch priority. (4096 is the value of the least-significant bit of a 4-bit switch priority value.)

When y ou enter the spanning-tree mst instance-id root secondary command, because of support for the extended system ID, the software changes the switch priority from the default value (32768) to 28672. If the root switch fails, this switch becomes the next root switch (if the other switches in the network use the default switch priority of 32768 and are therefore unlikely to become the root switch).

Examples

This example shows how to configure the switch as the root switch for instance 10 with a network diameter of 4:

This example shows how to configure the switch as the secondary root switch for instance 10 with a network diameter of 4:

You can verify your settings by entering the show spanning-tree mst instance-id privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 128.

 

Command History

 

Usage Guidelines

If the variable vlan-id is omitted, the command applies to the spanning-tree instance associated with VLAN 1.

You can set the priority on a VLAN that has no interfaces assigned to it. The setting takes effect when you assign the interface to the VLAN.

If you configure an interface with both the spanning-tree vlan vlan-id port-priority priority command and the spanning-tree port-priority priority command, the spanning-tree vlan vlan-id port-priority priority command takes effect.

If your switch is a member of a switch stack, you must use the spanning-tree [ vlan vlan-id ] cost cost interface configuration command instead of the spanning-tree [ vlan vlan-id ] port-priority priority interface configuration command to select an interface to put in the forwarding state. Assign lower cost values to interfaces that you want selected first and higher cost values that you want selected last.

Examples

This example shows how to increase the likelihood that a port will be put in the forwarding state if a loop occurs:

This example shows how to set the port-priority value on VLANs 20 to 25:

You can verify your settings by entering the show spanning-tree interface interface-id privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The BPDU filtering, the BPDU guard, and the Port Fast features are disabled on all interfaces unless they are individually configured.

 

Command History

 

Usage Guidelines

You can enable these features when the switch is operating in the per-VLAN spanning-tree plus (PVST+) rapid-PVST+, or the multiple spanning-tree (MST) mode.

Use the spanning-tree portfast bpdufilter default global configuration command to globally enable BPDU filtering on interfaces that are Port Fast-enabled (the interfaces are in a Port Fast-operational state). The interfaces still send a few BPDUs at link-up before the switch begins to filter outbound BPDUs. You should globally enable BPDU filtering on a switch so that hosts connected to switch interfaces do not receive BPDUs. If a BPDU is received on a Port Fast-enabled interface, the interface loses its Port Fast-operational status and BPDU filtering is disabled.

You can override the spanning-tree portfast bpdufilter default global configuration command by using the spanning-tree bdpufilter interface configuration command.

Caution Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in spanning-tree loops.

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Use the spanning-tree portfast bpduguard default global configuration command to globally enable BPDU guard on interfaces that are in a Port Fast-operational state. In a valid configuration, Port Fast-enabled interfaces do not receive BPDUs. Receiving a BPDU on a Port Fast-enabled interface signals an invalid configuration, such as the connection of an unauthorized device, and the BPDU guard feature puts the interface in the error-disabled state. The BPDU guard feature provides a secure response to invalid configurations because you must manually put the interface back in service. Use the BPDU guard feature in a service-provider network to prevent an access port from participating in the spanning tree.

You can override the spanning-tree portfast bpduguard default global configuration command by using the spanning-tree bdpuguard interface configuration command.

Use the spanning-tree portfast default global configuration command to globally enable the Port Fast feature on all nontrunking interfaces. Configure Port Fast only on interfaces that connect to end stations; otherwise, an accidental topology loop could cause a data packet loop and disrupt switch and network operation. A Port Fast-enabled interface moves directly to the spanning-tree forwarding state when linkup occurs without waiting for the standard forward-delay time.

You can override the spanning-tree portfast default global configuration command by using the spanning-tree portfast interface configuration command. You can use the no spanning-tree portfast default global configuration command to disable Port Fast on all interfaces unless they are individually configured with the spanning-tree portfast interface configuration command.

Examples

This example shows how to globally enable the BPDU filtering feature:

This example shows how to globally enable the BPDU guard feature:

This example shows how to globally enable the Port Fast feature on all nontrunking interfaces:

You can verify your settings by entering the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The Port Fast feature is disabled on all interfaces; however, it is automatically enabled on dynamic-access ports.

 

Command History

 

Usage Guidelines

Use this feature only on interfaces that connect to end stations; otherwise, an accidental topology loop could cause a data packet loop and disrupt switch and network operation.

To enable Port Fast on trunk ports, you must use the spanning-tree portfast trunk interface configuration command. The spanning-tree portfast command is not supported on trunk ports.

You can enable this feature when the switch is operating in the per-VLAN spanning-tree plus (PVST+), rapid-PVST+, or the multiple spanning-tree (MST) mode.

This feature affects all VLANs on the interface.

An interface with the Port Fast feature enabled is moved directly to the spanning-tree forwarding state without the standard forward-time delay.

You can use the spanning-tree portfast default global configuration command to globally enable the Port Fast feature on all nontrunking interfaces. However, the spanning-tree portfast interface configuration command can override the global setting.

If you configure the spanning-tree portfast default global configuration command, you can disable Port Fast on an interface that is not a trunk interface by using the spanning-tree portfast disable interface configuration command.

Examples

This example shows how to enable the Port Fast feature on a port:

You can verify your settings by entering the show running-config privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is 6.

 

Command History

 

Usage Guidelines

Increasing the transmit hold-count value can have a significant impact on CPU utilization when the switch is in rapid-per-VLAN spanning-tree plus (rapid-PVST+) mode. Decreasing this value might slow down convergence. We recommend using the default setting.

Examples

This example shows how to set the transmit hold count to 8:

You can verify your setting by entering the show spanning-tree mst privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

UplinkFast is disabled.

The update rate is 150 packets per second.

 

Command History

 

Usage Guidelines

Use this command only on access switches.

You can configure the UplinkFast feature for rapid PVST+ or for multiple spanning-tree (MST) mode, but the feature remains disabled (inactive) until you change the spanning-tree mode to PVST+.

When you enable UplinkFast, it is enabled for the entire switch and cannot be enabled for individual VLANs.

When you enable or disable UplinkFast, cross-stack UplinkFast (CSUF) also is automatically enabled or disabled on all nonstack port interfaces. CSUF accelerates the choice of a new root port when a link or switch fails or when spanning tree reconfigures itself.

When UplinkFast is enabled, the switch priority of all VLANs is set to 49152. If you change the path cost to a value less than 3000 and you enable UplinkFast or UplinkFast is already enabled, the path cost of all interfaces and VLAN trunks is increased by 3000 (if you change the path cost to 3000 or above, the path cost is not altered). The changes to the switch priority and the path cost reduces the chance that a switch will become the root switch.

When UplinkFast is disabled, the switch priorities of all VLANs and path costs of all interfaces are set to default values if you did not modify them from their defaults.

When spanning tree detects that the root port has failed, UplinkFast immediately changes to an alternate root port, changing the new root port directly to forwarding state. During this time, a topology change notification is sent.

Do not enable the root guard on interfaces that will be used by the UplinkFast feature. With UplinkFast, the backup interfaces (in the blocked state) replace the root port in the case of a failure. However, if root guard is also enabled, all the backup interfaces used by the UplinkFast feature are placed in the root-inconsistent state (blocked) and prevented from reaching the forwarding state.

If you set the max-update-rate to 0, station-learning frames are not generated, so the spanning-tree topology converges more slowly after a loss of connectivity.

Examples

This example shows how to enable UplinkFast:

You can verify your setting by entering the show spanning-tree summary privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

Spanning tree is enabled on all VLANs.

The forward-delay time is 15 seconds.

The hello time is 2 seconds.

The max-age is 20 seconds.

The primary root switch priority is 24576.

The secondary root switch priority is 28672.

 

Command History

 

Usage Guidelines

Disabling the STP causes the VLAN to stop participating in the spanning-tree topology. Interfaces that are administratively down remain down. Received BPDUs are forwarded like other multicast frames. The VLAN does not detect and prevent loops when STP is disabled.

You can disable the STP on a VLAN that is not currently active and verify the change by using the show running-config or the show spanning-tree vlan vlan-id privileged EXEC command. The setting takes effect when the VLAN is activated.

When disabling or re-enabling the STP, you can specify a range of VLANs that you want to disable or enable.

When a VLAN is disabled and then enabled, all assigned VLANs continue to be its members. However, all spanning-tree bridge parameters are returned to their previous settings (the last setting before the VLAN was disabled).

You can enable spanning-tree options on a VLAN that has no interfaces assigned to it. The setting takes effect when you assign interfaces to it.

When setting the max-age seconds, if a switch does not receive BPDUs from the root switch within the specified interval, it recomputes the spanning-tree topology. The max-age setting must be greater than the hello-time setting.

The spanning-tree vlan vlan-id root command should be used only on backbone switches.

When you enter the spanning-tree vlan vlan-id root command, the software checks the switch priority of the current root switch for each VLAN. Because of the extended system ID support, the switch sets the switch priority for the specified VLAN to 24576 if this value will cause this switch to become the root for the specified VLAN. 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.)

When you enter the spanning-tree vlan vlan-id root secondary command, because of support for the extended system ID, the software changes the switch priority from the default value (32768) to 28672. If the root switch should fail, this switch becomes the next root switch (if the other switches in the network use the default switch priority of 32768, and therefore, are unlikely to become the root switch).

Examples

This example shows how to disable the STP on VLAN 5:

You can verify your setting by entering the show spanning-tree privileged EXEC command. In this instance, VLAN 5 does not appear in the list.

This example shows how to set the spanning-tree forwarding time to 18 seconds for VLANs 20 and 25:

This example shows how to set the spanning-tree hello-delay time to 3 seconds for VLANs 20 to 24:

This example shows how to set spanning-tree max-age to 30 seconds for VLAN 20:

This example shows how to reset the max-age parameter to the default value for spanning-tree instance 100 and 105 to 108:

This example shows how to set the spanning-tree priority to 8192 for VLAN 20:

This example shows how to configure the switch as the root switch for VLAN 10 with a network diameter of 4:

This example shows how to configure the switch as the secondary root switch for VLAN 10 with a network diameter of 4:

You can verify your settings by entering the show spanning-tree vlan vlan-id privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The default is auto.

 

Command History

 

Usage Guidelines

You cannot configure speed on the 10-Gigabit Ethernet ports.

Except for the 1000BASE-T SFP modules, if an SFP module port is connected to a device that does not support autonegotiation, you can configure the speed to not negotiate (nonegotiate ).

If the speed is set to auto, the switch negotiates with the device at the other end of the link for the speed setting and then forces the speed setting to the negotiated value. The duplex setting remains as configured on each end of the link, which could result in a duplex setting mismatch.

If both ends of the line support autonegotiation, we highly recommend the default autonegotiation settings. If one interface supports autonegotiation and the other end does not, do use the auto setting on the supported side, but set the duplex and speed on the other side.

Caution Changing the interface speed and duplex mode configuration might shut down and re-enable the interface during the reconfiguration.

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For guidelines on setting the switch speed and duplex parameters, see the “Configuring Interface Characteristics” chapter in the software configuration guide for this release.

Examples

This example shows how to set the speed on a port to 100 Mb/s:

This example shows how to set a port to autonegotiate at only 10 Mb/s:

This example shows how to set a port to autonegotiate at only 10 or 100 Mb/s:

You can verify your settings by entering the show interfaces privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

The port is not rate limited and is set to 100 percent.

 

Command History

 

Usage Guidelines

If you configure this command to 80 percent, the port is idle 20 percent of the time. The line rate drops to 80 percent of the connected speed. These values are not exact because the hardware adjusts the line rate in increments of six.

This command is not available on a 10-Gigabit Ethernet interface.

Note The egress queue default settings are suitable for most situations. You should change them only when you have a thorough understanding of the egress queues and if these settings do not meet your quality of service (QoS) solution.

Examples

This example shows how to limit a port to 800 Mb/s:

You can verify your settings by entering the show mls qos interface [ interface-id ] queueing privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

Weight1 is set to 25. Weight2, weight3, and weight4 are set to 0, and these queues are in shared mode.

 

Command History

 

Usage Guidelines

In shaped mode, the queues are guaranteed a percentage of the bandwidth, and they are rate-limited to that amount. Shaped traffic does not use more than the allocated bandwidth even if the link is idle. Use shaping to smooth bursty traffic or to provide a smoother output over time.

The shaped mode overrides the shared mode.

If you configure a shaped queue weight to 0 by using the srr-queue bandwidth shape interface configuration command, this queue participates in shared mode. The weight specified with the srr-queue bandwidth shape command is ignored, and the weights specified with the srr-queue bandwidth share interface configuration command for a queue come into effect.

When configuring queues for the same port for both shaping and sharing, make sure that you configure the lowest numbered queue for shaping.

This command is not available on a 10-Gigabit Ethernet interface.

Note The egress queue default settings are suitable for most situations. You should change them only when you have a thorough understanding of the egress queues and if these settings do not meet your QoS solution.

Examples

This example shows how to configure the queues for the same port for both shaping and sharing. Because the weight ratios for queues 2, 3, and 4 are set to 0, these queues operate in shared mode. The bandwidth weight for queue 1 is 1/8, which is 12.5 percent. Queue 1 is guaranteed this bandwidth and limited to it; it does not extend its slot to the other queues even if the other queues have no traffic and are idle. Queues 2, 3, and 4 are in shared mode, and the setting for queue 1 is ignored. The bandwidth ratio allocated for the queues in shared mode is 4/(4+4+4), which is 33 percent:

You can verify your settings by entering the show mls qos interface [ interface-id ] queueing privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Defaults

Weight1, weight2, weight3, and weight4 are 25 (1/4 of the bandwidth is allocated to each queue).

 

Command History

 

Usage Guidelines

The absolute value of each weight is meaningless, and only the ratio of parameters is used.

In shared mode, the queues share the bandwidth among them according to the configured weights. The bandwidth is guaranteed at this level but not limited to it. For example, if a queue empties and does not require a share of the link, the remaining queues can expand into the unused bandwidth and share it among themselves.

If you configure a shaped queue weight to 0 by using the srr-queue bandwidth shape interface configuration command, this queue participates in SRR shared mode. The weight specified with the srr-queue bandwidth shape command is ignored, and the weights specified with the srr-queue bandwidth share interface configuration command for a queue take effect.

When configuring queues for the same port for both shaping and sharing, make sure that you configure the lowest numbered queue for shaping.

Note The egress queue default settings are suitable for most situations. You should change them only when you have a thorough understanding of the egress queues and if these settings do not meet your QoS solution.

Examples

This example shows how to configure the weight ratio of the SRR scheduler running on an egress port. Four queues are used. The bandwidth ratio allocated for each queue in shared mode is 1/(1+2+3+4), 2/(1+2+3+4), 3/(1+2+3+4), and 4/(1+2+3+4), which is 10 percent, 20 percent, 30 percent, and 40 percent for queues 1, 2, 3, and 4. This means that queue 4 has four times the bandwidth of queue 1, twice the bandwidth of queue 2, and one-and-a-third times the bandwidth of queue 3.

You can verify your settings by entering the show mls qos interface [ interface-id ] queueing privileged EXEC command.

 

Related Commands

 

Syntax Description

 

Command Default

Persistent MAC address is disabled. The MAC address of the stack is always that of the stack master.

When the command is entered with no value, the default time before the MAC address changes is four minutes. We recommend that you configure an explicit value for this command

 

Command History

 

Usage Guidelines

The MAC address of the switch stack is determined by the MAC address of the stack master. In the default state (persistent MAC address disabled), if a new switch becomes stack master, the stack MAC address changes to the MAC address of the new stack master.

When persistent MAC address is enabled, the stack MAC address does not change for a time period. During that time, if the previous stack master rejoins the stack as a stack member, the stack retains its MAC address for as long as that switch is in the stack. If the previous stack master does not rejoin the stack during the specified time period, the switch stack takes the MAC address of the new stack master as the stack MAC address.

You can set the time period to be from 0 to 60 minutes.

• If you enter the command with no value, the default delay is 4 minutes.
• If you enter 0, the stack continues to use the current stack MAC address until you enter the no stack-mac persistent timer command.
• If you enter a time delay of 1 to 60 minutes, the stack MAC address of the previous stack master is used until the configured time period expires or until you enter the no stack-mac persistent timer command.

Note When you enter the stack-mac persistent timer command with or without keywords, a message appears warning that traffic might be lost if the old master MAC address appears elsewhere in the network domain. You should use this feature cautiously.

If you enter the no stack-mac persistent timer command after a switchover, before the time expires, the switch stack moves to the current stack master MAC address.

If the whole stack reloads, when it comes back up, the MAC address of the stack master is the stack MAC address.

Examples

This example shows how to configure the persistent MAC address feature, with the warning messages for each configuration. It also shows how to verify the configuration:

You can verify your settings by entering either of two privileged EXEC commands:

• show running-config —If enabled, stack-mac persistent timer and the time in minutes appears in the output.
• show switch —If enabled, Mac persistency wait time and the number of minutes appears in the output.

 

Related Commands

 

Syntax Description

 

Defaults

Broadcast, multicast, and unicast storm control are disabled.

The default action is to filter traffic and to not send an SNMP trap.

 

Command History

 

Usage Guidelines