Cisco ME 3400E Ethernet Access Switch Command Reference, Rel. 12.2(58)SE

shutdown

Use the shutdown interface configuration command to disable an interface. Use the no form of this command to restart a disabled interface.

shutdown

no shutdown

Syntax Description

This command has no arguments or keywords.

Command Modes

Interface configuration

Command History

Usage Guidelines

The shutdown command causes a port to stop forwarding. The default state for a user network interface (UNI) or enhanced network interface (ENI) is shut down. Before you can configure a UNI or ENI, you must enable it with the no shutdown command. Network node interfaces (NNIs) are enabled by default.

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:

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# shutdown

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# no shutdown

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

Related Commands

shutdown vlan

Use the shutdown vlan global configuration command to shut down (suspend) local traffic on the specified VLAN. Use the no form of this command to restart local traffic on the VLAN.

shutdown vlan vlan-id

no shutdown vlan vlan-id

Syntax Description

Defaults

No default is defined.

Command Modes

Global configuration

Command History

Usage Guidelines

Use the shutdown VLAN configuration command to shut down local traffic on any VLAN, including extended-range VLANs (1006-4094).

Examples

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

Switch(config)# shutdown vlan 2

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

Related Commands

snmp mib rep trap-rate

Use the snmp mib rep trap-rate global configuration command to configure the sending of Resilient Ethernet Protocol (REP) SNMP traps when there is a link operational status or port role change. Use the no version of the command to disable sending of the REP trap.

snmp mib rep trap-rate value

no snmp mib rep trap-rate

Syntax Description

Defaults

Sending REP traps is disabled.

Command Modes

Global configuration

Command History

Usage Guidelines

Use this command to enable the switch to send REP specific traps corresponding to link operational status changes and port role changes.

Examples

This example configures the switch to send REP traps at a rate of 10 per second:

Switch(config)# snmp mib rep trap-rate 10 

Related Commands

snmp-server enable traps

Use the snmp-server enable traps global configuration command to enable the switch to send Simple Network Management Protocol (SNMP) notifications for various traps or inform requests to the network management system (NMS). Use the no form of this command to return to the default setting.

snmp-server enable traps [bgp | bridge [newroot] [topologychange] | config | copy-config | cpu threshold | {dot1x [auth-fail-vlan | guest-vlan | no-auth-fail-vlan | no-guest-vlan]} | entity | envmon [fan | shutdown | status | supply | temperature] | ethernet | flash | hsrp | ipmulticast | mac-notification [change] [move] [threshold] | msdp | ospf [cisco-specific | errors | lsa | rate-limit | retransmit | state-change] | pim [invalid-pim-message | neighbor-change | rp-mapping-change] | port-security [trap-rate value] | rtr | snmp [authentication | coldstart | linkdown | linkup | warmstart] | storm-control trap-rate value | stpx [inconsistency] [root-inconsistency] [loop-inconsistency] | syslog | transceiver all | tty | vlan-membership | vlancreate | vlandelete]

no snmp-server enable traps [bgp | bridge [newroot] [topologychange] | config | copy-config | cpu threshold | {dot1x [auth-fail-vlan | guest-vlan | no-auth-fail-vlan | no-guest-vlan]} | entity | envmon [fan | shutdown | status | supply | temperature] | ethernet | flash | hsrp | ipmulticast | mac-notification [change] [move] [threshold] | msdp | ospf [cisco-specific | errors | lsa | rate-limit | retransmit | state-change] | pim [invalid-pim-message | neighbor-change | rp-mapping-change] | port-security [trap-rate value] | rtr | snmp [authentication | coldstart | linkdown | linkup | warmstart] | storm-control trap-rate value | stpx [inconsistency] [root-inconsistency] [loop-inconsistency] | syslog | transceiver all | tty | vlan-membership | vlancreate | vlandelete]

Syntax Description

Note Though visible in the command-line help strings, the fru-ctrl insertion and removal, and vtp keywords are not supported. 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 Modes

Global configuration

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 trap 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.

SNMP transceiver traps apply to SFPs that support DoM-capable transceivers installed on the switch. The sensor values are polled every 10 minutes, which is how often the user sees traps or alarms.

Examples

This example shows how to send port security traps to the NMS:

Switch(config)# snmp-server enable traps port security

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

Related Commands

snmp-server host

Use the snmp-server host global configuration command to specify the recipient (host) of a Simple Network Management Protocol (SNMP) notification operation. Use the no form of this command to remove the specified host.

snmp-server host host-addr [informs | traps] [version {1 | 2c | 3 {auth | noauth| priv}] [vrf vrf-instance] {community-string [notification-type]}

no snmp-server host host-addr [informs | traps] [version {1 | 2c | 3 {auth | noauth | priv}] [vrf vrf-instance] community-string

Syntax Description

Note Though visible in the command-line help strings, the fru-ctrl, and vtp keywords are not supported.

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 Modes

Global configuration

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:

Switch(config)# snmp-server community comaccess ro 10

Switch(config)# snmp-server host 172.20.2.160 comaccess

Switch(config)# access-list 10 deny any

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:

Switch(config)# snmp-server enable traps

Switch(config)# snmp-server host myhost.cisco.com comaccess snmp 

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

Switch(config)# snmp-server enable traps

Switch(config)# snmp-server host myhost.cisco.com public

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

Related Commands

snmp trap mac-notification change

Use the snmp trap mac-notification change interface configuration command to enable the Simple Network Management Protocol (SNMP) MAC address notification trap on a specific Layer 2 interface. Use the no form of this command to return to the default setting.

snmp trap mac-notification change {added | removed}

no snmp trap mac-notification change {added | removed}

Syntax Description

Defaults

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

Command Modes

Interface configuration

Command History

Usage Guidelines

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

Examples

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

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# snmp trap mac-notification change added

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

Related Commands

spanning-tree

Use the spanning-tree interface configuration command with no keywords on an enhanced network interface (ENI) to enable a spanning-tree instance on the interface. Use the no form of this command to return to the default setting of disabled.

spanning-tree

no spanning-tree

Syntax Description

This command has no arguments or keywords.

Defaults

The Spanning-Tree Protocol (STP) is disabled on ENIs.

Command Modes

Interface configuration

Command History

Usage Guidelines

This command is supported only on ENIs and on EtherChannel port channels that contain ENIs.

STP is not supported on user network interfaces (UNIs) and it is disabled by default on ENIs. Use this command to enable SPT on an ENI. To set a port as an ENI, enter the port-type eni interface configuration command. Once STP is enabled on an ENI, all other STP interface configuration commands are available on the interface.

The switch supports only one spanning-tree instance on a VLAN. When NNIs and ENIs with spanning tree enabled are in the same VLAN, they belong to the same spanning-tree instance.

STP is enabled by default on NNIs. UNIs are typically customer-facing ports and do not participate in the spanning tree of the service provider. However, if you configure a customer-facing port as an ENI and enable spanning tree, the ENI could become the spanning tree root port unless you configure root guard on the port by using the spanning-tree guard root interface configuration command. A customer-facing ENI with STP enabled participates in the same spanning tree as the service-provider facing NNI.

Note Exercise caution when enabling STP on a customer-facing ENI.

Examples

This example shows how to enable STP on a port:

Switch(config)# interface fastethernet0/1

Switch(config-if)# port-type eni

Switch(config-if)# spanning-tree

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

Related Commands

spanning-tree bpdufilter

Use the spanning-tree bpdufilter interface configuration command on a network node interface (NNI) or enhanced network interface (ENI) with STP enabled to prevent the interface from sending or receiving bridge protocol data units (BPDUs). Use the no form of this command to return to the default setting.

spanning-tree bpdufilter {disable | enable}

no spanning-tree bpdufilter

Syntax Description

Defaults

BPDU filtering is disabled.

Command Modes

Interface configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure BPDU filtering only on NNIs or on ENIs on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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 STP port is the same as disabling spanning tree on it and can result in spanning-tree loops.

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

You can use the spanning-tree bpdufilter interface configuration command on an STP port 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:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# spanning-tree bpdufilter enable

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

Related Commands

spanning-tree bpduguard

Use the spanning-tree bpduguard interface configuration command on a network node interface (NNI) or enhanced network interface (ENI) with STP enabled to put the interface in the error-disabled state when it receives a bridge protocol data unit (BPDU). Use the no form of this command to return to the default setting.

spanning-tree bpduguard {disable | enable}

no spanning-tree bpduguard

Syntax Description

Defaults

BPDU guard is disabled.

Command Modes

Interface configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure BPDU guard only on NNIs or on ENIs on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

The BPDU guard feature provides a secure response to invalid configurations because you must manually put the STP port 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+), the rapid-PVST+, or the multiple spanning-tree (MST) mode.

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

You can use the spanning-tree bpduguard interface configuration command on an STP port 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:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# spanning-tree bpduguard enable

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

Related Commands

spanning-tree cost

Use the spanning-tree cost interface configuration command on a network node interface (NNI) or enhanced network interface (ENI) with STP enabled to set the path cost for spanning-tree calculations. If a loop occurs, spanning tree considers the path cost when selecting an interface to place in the forwarding state. Use the no form of this command to return to the default setting.

spanning-tree [vlan vlan-id] cost cost

no spanning-tree [vlan vlan-id] cost

Syntax Description

Defaults

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

•1000 Mbps—4

•100 Mbps—19

•10 Mbps—100

Command Modes

Interface configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure spanning-tree cost only on NNIs or on enhanced network interfaces (ENIs) on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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

If you configure an STP port 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:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# spanning-tree cost 250

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

Switch(config-if)# spanning-tree vlan 10,12-15,20 cost 300

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

Related Commands

spanning-tree etherchannel guard misconfig

Use the spanning-tree etherchannel guard misconfig global configuration command to display an error message when the switch detects an EtherChannel misconfiguration. Use the no form of this command to disable the feature.

spanning-tree etherchannel guard misconfig

no spanning-tree etherchannel guard misconfig

Syntax Description

This command has no arguments or keywords.

Defaults

EtherChannel guard is enabled on the switch.

Command Modes

Global configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). This command affects only network node interfaces (NNIs) or enhanced network interfaces (ENIs) on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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

PM-4-ERR_DISABLE: Channel-misconfig error detected on [chars], putting [chars] in 
err-disable state.

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:

Switch(config)# spanning-tree etherchannel guard misconfig

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

Related Commands

spanning-tree extend system-id

Use the spanning-tree extend system-id global configuration command to enable the extended system ID feature.

spanning-tree extend system-id

Note Though visible in the command-line help strings, the no version of this command is not supported. You cannot disable the extended system ID feature.

Syntax Description

This command has no arguments or keywords.

Defaults

The extended system ID is enabled.

Command Modes

Global configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). This command affects only network node interfaces (NNIs) or enhanced network interfaces (ENIs) on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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.

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

spanning-tree guard

Use the spanning-tree guard interface configuration command on a network node interface (NNI) or enhanced network interface (ENI) with STP enabled to enable root guard or loop guard on all the VLANs associated with the selected NNI. Root guard restricts which interface is allowed to be the spanning-tree root port or the path-to-the root for the switch. Loop guard prevents alternate or root ports from becoming designated ports when a failure creates a unidirectional link. Use the no form of this command to return to the default setting.

spanning-tree guard {loop | none | root}

no spanning-tree guard

Syntax Description

Defaults

Root guard is disabled.

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

Command Modes

Interface configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure spanning-tree guard only on NNIs or on enhanced network interfaces ENIs on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

You can enable root guard or loop guard when the switch is operating in the per-VLAN spanning-tree plus (PVST+), the 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 NNI. If this interface is in the root-inconsistent (blocked) state, it automatically transitions to the listening state.

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 on an STP interface. 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 on an STP interface.

Examples

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

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# spanning-tree guard root

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

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# spanning-tree guard loop

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

Related Commands

spanning-tree link-type

Use the spanning-tree link-type interface configuration command on a network node interface (NNI) or enhanced network interface (ENI) with STP enabled to override the default link-type setting, which is determined by the duplex mode of the STP port, and to enable rapid spanning-tree transitions to the forwarding state. Use the no form of this command to return to the default setting.

spanning-tree link-type {point-to-point | shared}

no spanning-tree link-type

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 Modes

Interface configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure spanning-tree link type only on NNIs or on ENIs on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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:

Switch(config-if)# spanning-tree link-type shared

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

spanning-tree loopguard default

Use the spanning-tree loopguard default global configuration command to enable loopguard by default on all network node interfaces (NNIs) or enhanced network interface (ENIs) with STP enabled. Enabling loopguard prevents alternate or root ports from becoming designated ports because of a failure that leads to a unidirectional link. Use the no form of this command to return to the default setting.

spanning-tree loopguard default

no spanning-tree loopguard default

Syntax Description

This command has no arguments or keywords.

Defaults

Loop guard is disabled.

Command Modes

Global configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is supported only on NNIs or on ENIs on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

This command has no effect on user network interfaces (UNIs).

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 STP ports 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:

Switch(config)# spanning-tree loopguard default

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

Related Commands

spanning-tree mode

Use the spanning-tree mode global configuration command to enable per-VLAN spanning-tree plus (PVST+), rapid PVST+, or multiple spanning tree (MST) on your switch. Use the no form of this command to return to the default setting.

spanning-tree mode {mst | pvst | rapid-pvst}

no spanning-tree mode

Syntax Description

Defaults

The default mode is rapid PVST+.

Command Modes

Global configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is supported on the switch only on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

STP is not supported on user network interfaces (UNIs).

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.

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.

Examples

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

Switch(config)# spanning-tree mode mst

This example shows to enable PVST+ on the switch:

Switch(config)# spanning-tree mode pvst

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

Related Commands

spanning-tree mst configuration

Use the spanning-tree mst configuration global configuration command to enter multiple spanning-tree (MST) configuration mode through which you configure the MST region. Use the no form of this command to return to the default settings.

spanning-tree mst configuration

no spanning-tree mst configuration

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 Modes

Global configuration

Command History

Usage Guidelines

On the Cisco ME switch, spanning-tree MST configuration is supported only on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

User network interfaces (UNIs) do not participate in Spanning Tree Protocol (STP).

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 0 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 supports up to 16 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:

Switch# spanning-tree mst configuration

Switch(config-mst)# instance 1 vlan 10-20

Switch(config-mst)# name region1

Switch(config-mst)# revision 1

Switch(config-mst)# show pending

Pending MST configuration

Name      [region1]

Revision  1

Instance  Vlans Mapped

--------  ---------------------

0         1-9,21-4094

1         10-20

-------------------------------

Switch(config-mst)# exit

Switch(config)#

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:

Switch(config-mst)# instance 2 vlan 1-100

Switch(config-mst)# no instance 2 vlan 40-60

Switch(config-mst)# instance 10 vlan 10

Switch(config-mst)# no instance 2

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

Related Commands

spanning-tree mst cost

Use the spanning-tree mst cost interface configuration command on a network node interface (NNI) or an enhanced network interface (ENI) with STP enabled to set the path cost for multiple spanning-tree (MST) calculations. If a loop occurs, spanning tree considers the path cost when selecting an interface to put in the forwarding state. Use the no form of this command to return to the default setting.

spanning-tree mst instance-id cost cost

no spanning-tree mst instance-id cost

Syntax Description

Defaults

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

•1000 Mbps—20000

•100 Mbps—200000

•10 Mbps—2000000

Command Modes

Interface configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure path cost only on NNIs or on ENIs on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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:

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# spanning-tree mst 2,4 cost 250

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

Related Commands

spanning-tree mst forward-time

Use the spanning-tree mst forward-time global configuration command to set the forward-delay time for all multiple spanning-tree (MST) instances. The forwarding time specifies how long each of the listening and learning states last before the interface begins forwarding. Use the no form of this command to return to the default setting.

spanning-tree mst forward-time seconds

no spanning-tree mst forward-time

Syntax Description

Defaults

The default is 15 seconds.

Command Modes

Global configuration

Command History

Usage Guidelines

On the Cisco ME switch, spanning-tree MST configuration is supported only on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which Spanning-Tree Protocol (STP) has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

User network interfaces (UNIs) do not participate in STP.

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:

Switch(config)# spanning-tree mst forward-time 18

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

Related Commands

spanning-tree mst hello-time

Use the spanning-tree mst hello-time global configuration command to set the interval between hello bridge protocol data units (BPDUs) sent by root switch configuration messages. Use the no form of this command to return to the default setting.

spanning-tree mst hello-time seconds

no spanning-tree mst hello-time

Syntax Description

Defaults

The default is 2 seconds.

Command Modes

Global configuration

Command History

Usage Guidelines

On the Cisco ME switch, spanning-tree MST configuration is supported only on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which Spanning-Tree Protocol (STP) has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

User network interfaces (UNIs) do not participate in STP.

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:

Switch(config)# spanning-tree mst hello-time 3

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

Related Commands

spanning-tree mst max-age

Use the spanning-tree mst max-age global configuration command to set the interval between messages that the spanning tree receives from the root switch. If a switch does not receive a bridge protocol data unit (BPDU) message from the root switch within this interval, it recomputes the spanning-tree topology. Use the no form of this command to return to the default setting.

spanning-tree mst max-age seconds

no spanning-tree mst max-age

Syntax Description

Defaults

The default is 20 seconds.

Command Modes

Global configuration

Command History

Usage Guidelines

On the Cisco ME switch, spanning-tree MST configuration is supported only on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which Spanning Tree Protocol (STP) has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

User network interfaces (UNIs) do not participate in STP.

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:

Switch(config)# spanning-tree mst max-age 30

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

Related Commands

spanning-tree mst max-hops

Use the spanning-tree mst max-hops global configuration command to set the number of hops in a region before the bridge protocol data unit (BPDU) is discarded and the information held for an interface is aged. Use the no form of this command to return to the default setting.

spanning-tree mst max-hops hop-count

no spanning-tree mst max-hops

Syntax Description

Defaults

The default is 20 hops.

Command Modes

Global configuration

Command History

Usage Guidelines

On the Cisco ME switch, spanning-tree MST configuration is supported only on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which Spanning Tree Protocol (STP) has been enabled. To set a port as an NNI or ENI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

User network interfaces (UNIs) do not participate in STP.

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:

Switch(config)# spanning-tree mst max-hops 10

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

Related Commands

spanning-tree mst port-priority

Use the spanning-tree mst port-priority interface configuration command on a network node interface (NNI) or enhanced network interface (ENI) with STP enabled to configure an interface priority. If a loop occurs, the Multiple Spanning Tree Protocol (MSTP) can find the interface to put in the forwarding state. Use the no form of this command to return to the default setting.

spanning-tree mst instance-id port-priority priority

no spanning-tree mst instance-id port-priority

Syntax Description

Defaults

The default is 128.

Command Modes

Interface configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs). You can configure spanning-tree MST port priority only on NNIs or on ENIs on which STP has been enabled. To set a port as an ENI or NNI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

You can assign higher priority values (lower numerical values) to STP port that you want selected first and lower priority values (higher numerical values) that you want selected last. If all STP ports 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.

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:

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# spanning-tree mst 20,22 port-priority 0

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

Related Commands

spanning-tree mst pre-standard

Use the spanning-tree mst pre-standard interface configuration command to configure a port to send only prestandard bridge protocol data units (BPDUs).

spanning-tree mst pre-standard

no spanning-tree mst pre-standard

Syntax Description

This command has no arguments or keywords.

Command Default

The default state is automatic detection of prestandard neighbors.

Command Modes

Interface configuration

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:

Switch(config-if)# spanning-tree mst pre-standard

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

Related Commands

spanning-tree mst priority

Use the spanning-tree mst priority global configuration command to set the switch priority for the specified spanning-tree instance. Use the no form of this command to return to the default setting.

spanning-tree mst instance-id priority priority

no spanning-tree mst instance-id priority

Syntax Description

Defaults

The default is 32768.

Command Modes

Global configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs); it is only supported on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which STP has been enabled. To set a port as an ENI or NNI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

Examples

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

Switch(config)# spanning-tree mst 20-21 priority 8192

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

Related Commands

spanning-tree mst root

Use the spanning-tree mst root global configuration command to configure the multiple spanning-tree (MST) root switch priority and timers based on the network diameter. Use the no form of this command to return to the default settings.

spanning-tree mst instance-id root {primary | secondary} [diameter net-diameter
[hello-time seconds]]

no spanning-tree mst instance-id root

Syntax Description

Defaults

The primary root switch priority is 24576.

The secondary root switch priority is 28672.

The hello time is 2 seconds.

Command Modes

Global configuration

Command History

Usage Guidelines

Spanning Tree Protocol (STP) is not supported on user network interfaces (UNIs); it is only supported on network node interfaces (NNIs) or on enhanced network interfaces (ENIs) on which STP has been enabled. To set a port as an ENI or NNI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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

When 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 you 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:

Switch(config)# spanning-tree mst 10 root primary diameter 4

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

Switch(config)# spanning-tree mst 10 root secondary diameter 4 

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

Related Commands

spanning-tree port-priority

Use the spanning-tree port-priority interface configuration command on a network node interface (NNI) or an enhanced network interface (ENI) on which Spanning Tree Protocol (STP) has been enabled to configure an interface priority. If a loop occurs, spanning tree can find the interface to put in the forwarding state. Use the no form of this command to return to the default setting.

spanning-tree [vlan vlan-id] port-priority priority

no spanning-tree [vlan vlan-id] port-priority

Syntax Description

Defaults

The default is 128.

Command Modes

Interface configuration

Command History

Usage Guidelines

STP is not supported on user network interfaces (UNIs). You can configure spanning-tree port priority only on NNIs or on ENIs on which STP has been enabled. To set a port as an ENI or NNI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

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 STP port to the VLAN.

If you configure an STP port 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.

Examples

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

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# spanning-tree vlan 20 port-priority 0

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

Switch(config-if)# spanning-tree vlan 20-25 port-priority 0

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

Related Commands

spanning-tree portfast (global configuration)

Use the spanning-tree portfast global configuration command to globally enable bridge protocol data unit (BPDU) filtering on Port Fast-enabled network node interfaces (NNIs) or enhanced network interfaces (ENIs) on which Spanning Tree Protocol (STP) has been enabled, to enable the BPDU guard feature on Port Fast-enabled STP ports, or the Port Fast feature on all nontrunking STP ports. The BPDU filtering feature prevents the switch STP port from sending or receiving BPDUs. The BPDU guard feature puts Port Fast-enabled STP ports that receive BPDUs in an error-disabled state. Use the no form of this command to return to the default settings.

spanning-tree portfast {bpdufilter default | bpduguard default | default}

no spanning-tree portfast {bpdufilter default | bpduguard default | default}

Syntax Description

Defaults

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

Command Modes

Global configuration

Command History

Usage Guidelines

STP is not supported on user network interfaces (UNIs) on the switch. Spanning-tree configuration affects only NNIs or ENIs on which STP has been enabled. To set a port as an ENI or NNI, enter the port-type {eni | nni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

UNIs are typically customer-facing ports and do not participate in the spanning tree of the service provider. However, if you configure a customer-facing port as an ENI and enable spanning tree, the ENI could become the spanning tree root port unless you configure root guard on the port by using the spanning-tree guard root interface configuration command. A customer-facing ENI with STP enabled participates in the same spanning tree as the service-provider facing NNI.

Note Exercise caution when enabling STP on a customer-facing ENI.

You can enable these features when the switch is operating in the per-VLAN spanning-tree plus (PVST+), the 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 STP ports that are Port Fast-enabled. The STP ports 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 STP ports do not receive BPDUs. If a BPDU is received on a Port Fast-enabled STP port, 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 on an STP port by using the spanning-tree bdpufilter interface configuration command.

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

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

Use the spanning-tree portfast default global configuration command to globally enable the Port Fast feature on all nontrunking STP ports. Configure Port Fast only on STP ports 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 STP port 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 on an STP port. You can use the no spanning-tree portfast default global configuration command to disable Port Fast on all STP ports 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:

Switch(config)# spanning-tree portfast bpdufilter default

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

Switch(config)# spanning-tree portfast bpduguard default

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

Switch(config)# spanning-tree portfast default

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

Related Commands

spanning-tree portfast (interface configuration)

Use the spanning-tree portfast interface configuration command on a network node interface (NNI) or an enhanced network interface (ENI) on which Spanning Tree Protocol (STP) has been enabled to enable the Port Fast feature on an STP port in all its associated VLANs. When the Port Fast feature is enabled, the STP port changes directly from a blocking state to a forwarding state without making the intermediate spanning-tree state changes. Use the no form of this command to return to the default setting.

spanning-tree portfast [disable | trunk]

no spanning-tree portfast

Syntax Description

Defaults

The Port Fast feature is disabled on all ports.

Command Modes

Interface configuration

Command History

Usage Guidelines

STP is not supported on user network interfaces (UNIs). You can enable the spanning-tree Port Fast feature only on NNIs or on ENIs on which STP has been enabled. To set a port as an NNI or ENI, enter the port-type {nni | eni} interface configuration command. To enable STP on an ENI, enter the spanning-tree interface configuration command.

Use this feature only on STP ports 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+), the rapid-PVST+, or the multiple spanning-tree (MST) mode.

This feature affects all VLANs on the STP port.

An NNI 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 STP port 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:

Switch(config)# interface gigabitethernet0/2

Switch(config-if)# spanning-tree portfast

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

Related Commands

spanning-tree vlan

Use the spanning-tree vlan global configuration command to configure spanning tree on a per-VLAN basis. Use the no form of this command to return to the default setting.

spanning-tree vlan vlan-id [forward-time seconds | hello-time seconds | max-age seconds |
priority priority | root {primary | secondary} [diameter net-diameter
[hello-time seconds]]]

no spanning-tree vlan vlan-id [forward-time | hello-time | max-age | priority | root]

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 Modes

Global configuration

Command History

Usage Guidelines

The switch does not support Spanning Tree Protocol (STP) on user network interfaces (UNIs). Only the switch network node interfaces (NNIs) or STP-enabled enhanced network interfaces (ENIs) in a VLAN participate in STP.

Disabling the STP causes the VLAN to stop participating in the spanning-tree topology. STP ports 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 STP ports 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:

Switch(config)# no spanning-tree 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:

Switch(config)# spanning-tree vlan 20,25 forward-time 18

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

Switch(config)# spanning-tree vlan 20-24 hello-time 3

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

Switch(config)# spanning-tree vlan 20 max-age 30

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

Switch(config)# no spanning-tree vlan 100, 105-108 max-age

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

Switch(config)# spanning-tree vlan 20 priority 8192

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

Switch(config)# spanning-tree vlan 10 root primary diameter 4

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

Switch(config)# spanning-tree vlan 10 root secondary diameter 4 

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

Related Commands

speed

Use the speed interface configuration command to specify the speed of a 10/100 Mbps or 10/100/1000 Mbps port. Use the no or default form of this command to return the port to its default value.

speed {10 | 100 | 1000 | auto [10 | 100 | 1000] | nonegotiate}

no speed

Note For speed configurations restrictions on small form-factor pluggable (SFP) module ports, see the "Usage Guidelines" section.

Note You cannot configure the speed on small form-factor pluggable (SFP) module ports, but you can configure the speed to not negotiate (nonegotiate) if they are connected to a device that does not support autonegotiation. See "Usage Guidelines" for exceptions when a 1000BASE-T SFP module is in the SFP module slot.

Syntax Description

Defaults

The default is auto.

Command Modes

Interface configuration

Command History

Usage Guidelines

You can configure the Fast Ethernet port speed as either 10 or 100 Mbps.

You can configure the Gigabit Ethernet port speed as 10, 100, or 1000 Mbps.

When a 1000BASE-T SFP module is in the SFP module slot, you can configure the speed as 10, 100, 1000, or auto but not to nonegotiate.

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.

Note For guidelines on setting the switch speed and duplex parameters, see the software configuration guide for this release.

Examples

This example shows how to set speed on a port to 100 Mbps:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# speed 100

This example shows how to set a port to autonegotiate at only 10 Mbps:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# speed auto 10

This example shows how to set a port to autonegotiate at only 10 or 100 Mbps:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# speed auto 10 100 

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

Related Commands

storm-control

Use the storm-control interface configuration command to enable broadcast, multicast, or unicast storm control and to set threshold levels on an interface. Use the no form of this command to return to the default setting.

storm-control {{broadcast | multicast | unicast} level {level [level-low] | bps bps [bps-low] | pps pps [pps-low]}} | {action {shutdown | trap}}

no storm-control {{broadcast | multicast | unicast} level} | {action {shutdown | trap}}

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 Modes

Interface configuration

Command History

Usage Guidelines

Storm control is supported on physical interfaces. You can also configure storm control on an EtherChannel. When storm control is configured on an EtherChannel, the storm control settings propagate to the EtherChannel physical interfaces.

If the port is a user network interface (UNI) or enhanced network interfaces (ENI), you must use the no shutdown interface configuration command to enable it before using the storm-control command. UNIs and ENIs are disabled by default. Network node interfaces (NNIs) are enabled by default.

The storm-control suppression level can be entered as a percentage of total bandwidth of the port, as a rate in packets per second at which traffic is received, or as a rate in bits per second at which traffic is received.

When specified as a percentage of total bandwidth, a suppression value of 100 percent means that no limit is placed on the specified traffic type. A value of level 0 0 means that all broadcast, multicast, or unicast traffic on that port is blocked. Storm control is enabled only when the rising suppression level is less than 100 percent. If no other storm-control configuration is specified, the default action is to filter the traffic causing the storm and to send no SNMP traps.

Note When the storm control threshold for multicast traffic is reached, all multicast traffic except control traffic, such as bridge protocol data unit (BDPU) and Cisco Discovery Protocol (CDP) frames, are blocked. However, the switch does not differentiate between routing updates, such as Open Shortest Path First (OSPF) and regular multicast data traffic, so both types of traffic are blocked.

The trap and shutdown options are independent of each other.

If you configure the action to be taken as shutdown (the port is error-disabled during a storm) when a packet storm is detected, you must use the no shutdown interface configuration command to bring the interface out of this state. If you do not specify the shutdown action, specify the action as trap (the switch generates a trap when a storm is detected).

When a storm occurs and the action is to filter traffic, if the falling suppression level is not specified, the switch blocks all traffic until the traffic rate drops below the rising suppression level. If the falling suppression level is specified, the switch blocks traffic until the traffic rate drops below this level.

When a broadcast storm occurs and the action is to filter traffic, the switch blocks only broadcast traffic.

For more information, see the software configuration guide for this release.

Examples

This example shows how to enable broadcast storm control with a 75.5-percent rising suppression level:

Switch(config-if)# storm-control broadcast level 75.5

This example shows how to enable unicast storm control on a port with a 87-percent rising suppression level and a 65-percent falling suppression level:

Switch(config-if)# storm-control unicast level 87 65

This example shows how to enable multicast storm control on a port with a 2000-packets-per-second rising suppression level and a 1000-packets-per-second falling suppression level:

Switch(config-if)# storm-control multicast level pps 2k 1k

This example shows how to enable the shutdown action on a port:

Switch(config-if)# storm-control action shutdown

You can verify your settings by entering the show storm-control privileged EXEC command.

Related Commands

switchport

Use the switchport interface configuration command with no keywords to put an interface that is in Layer 3 mode into Layer 2 mode for Layer 2 configuration. Use the no form of this command to put an interface in Layer 3 mode.

switchport

no switchport

Syntax Description

This command has no arguments or keywords.

Defaults

By default, all interfaces are in Layer 2 (switching) mode.

Command Modes

Interface configuration

Command History

Usage Guidelines

Use the no switchport command (without parameters) to set the interface to the routed-interface status and to erase all Layer 2 configurations. You must enter the no switchport command and then assign an IP address to the port.

If an interface is configured you must first enter the switchport command with no keywords before configuring switching characteristics on the port. Then you can enter additional switchport commands with keywords, as shown on the pages that follow.

Entering the no switchport command shuts the port down and then re-enables it, which might generate messages on the device to which the port is connected.

When you enter the switchport (or no switchport) command without keywords on an interface, the configuration information for the affected interface might be lost, and the interface returned to its default configuration.

Examples

This example shows how to change an interface from a Layer 2 (switching) port to a Layer 3 (routed) port.

Switch(config-if)# no switchport

This example shows how to return the port to switching mode:

Switch(config-if)# switchport

You can verify the switchport status of an interface by entering the show running-config privileged EXEC command.

Related Commands

switchport access vlan

Use the switchport access vlan interface configuration command to configure a port as a static-access or dynamic-access port. If the switchport mode is set to access (by using the switchport mode interface configuration command), use this command to set the port to operate as a member of the specified VLAN or to specify that the port uses VLAN Membership Policy Server (VMPS) protocol where VLAN assignment based on the incoming packets it receives. Use the no form of this command to reset the access VLAN mode to the default VLAN for the switch.

switchport access vlan {vlan-id | dynamic}

no switchport access vlan

Syntax Description

Defaults

The default access VLAN and trunk interface native VLAN is a VLAN corresponding to the platform or interface hardware.

A dynamic-access port is initially a member of no VLAN and receives its assignment based on the packet it receives.

Command Modes

Interface configuration

Command History

Usage Guidelines

The no switchport access vlan command resets the access mode VLAN to the appropriate default VLAN for the device.

The port must be in access mode before the switchport access vlan command can take effect.

An access port can be assigned to only one VLAN.

The VMPS server (such as a Catalyst 6500 series switch) must be configured before a port is configured as dynamic.

If the specified VLAN is configured as a UNI-ENI community VLAN, the interface is configured as UNI-ENI community port. Otherwise the port is configured as a UNI-ENI isolated port.

This command is supported on IEEE802.1Q tunnel ports.

These restrictions apply to dynamic-access ports:

•The dynamic keyword is not visible on network node interfaces (NNIs).

•The software implements the VLAN Query Protocol (VQP) client, which can query a VMPS such as a Catalyst 6500 series switch. The switch cannot be a VMPS servers. The VMPS server must be configured before a port is configured as dynamic.

•Use dynamic-access ports only to connect end stations. Connecting them to switches or routers (that use bridging protocols) can cause a loss of connectivity.

•Dynamic-access ports can only be in one VLAN and do not use VLAN tagging.

•Dynamic-access ports cannot be configured as:

–Members of an EtherChannel port group (dynamic-access ports cannot be grouped with any other port, including other dynamic ports).

–Source or destination ports in a static address entry.

–Monitor ports.

Examples

This example shows how to change a Layer 2 interface in access mode to operate in VLAN 2 instead of the default VLAN.

Switch(config-if)# switchport access vlan 2

You can verify your setting by entering the show interfaces interface-id switchport privileged EXEC command and examining information in the Administrative Mode and Operational Mode rows.

Related Commands

switchport backup interface

Use the switchport backup interface interface configuration command on a Layer 2 interface on the switch stack or on a standalone switch to configure Flex Links, a pair of interfaces that provide backup to each other. Use the no form of this command to remove the Flex Links configuration.

switchport backup interface [FastEthernet interface-id | GigabitEthernet interface-id | Port-channel interface-id] {mmu primary vlan interface-id | multicast fast-convergence | preemption {delay delay-time | mode} | prefer vlan vlan-id}

no switchport backup interface [FastEthernet interface-id | GigabitEthernet interface-id | Port-channel interface-id] {mmu primary vlan interface-id | multicast fast-convergence | preemption {delay delay-time | mode} | prefer vlan vlan-id}

Syntax Description

Defaults

The default is to have no Flex Links defined. Preemption mode is off. No preemption occurs. Preemption delay is set to 35 seconds.

Command Modes

Interface configuration

Command History

Usage Guidelines

With Flex Links configured, one link acts as the primary interface and forwards traffic, while the other interface is in standby mode, ready to begin forwarding traffic if the primary link shuts down. The interface being configured is referred to as the active link; the specified interface is identified as the backup link. The feature provides an alternative to the Spanning Tree Protocol (STP), allowing users to turn off STP and still retain basic link redundancy.

•This command is available only for Layer 2 interfaces.

•You can configure only one Flex Link backup link for any active link, and it must be a different interface from the active interface.

•An interface can belong to only one Flex Link pair. An interface can be a backup link for only one active link. An active link cannot belong to another Flex Link pair.

•A backup link does not have to be the same type (Fast Ethernet or Gigabit Ethernet, for instance) as the active link. However, you should configure both Flex Links with similar characteristics so that there are no loops or changes in behavior if the standby link begins to forward traffic.

•Neither of the links can be a port that belongs to an EtherChannel. However, you can configure two port channels (EtherChannel logical interfaces) as Flex Links, and you can configure a port channel and a physical interface as Flex Links, with either the port channel or the physical interface as the active link.

•If STP is configured on the switch, Flex Links do not participate in STP in all valid VLANs. If STP is not running, be sure that there are no loops in the configured topology.

Examples

This example shows how to configure two interfaces as Flex Links:

Switch# configure terminal 

Switch(conf)# interface fastethernet0/1

Switch(conf-if)# switchport backup interface fastethernet0/2

Switch(conf-if)# end

This example shows how to configure the Fast Ethernet interface to always preempt the backup:

Switch# configure terminal 

Switch(conf)# interface fastethernet0/1

Switch(conf-if)# switchport backup interface fastethernet0/2 preemption forced

Switch(conf-if)# end

This example shows how to configure the Fast Ethernet interface preemption delay time:

Switch# configure terminal 

Switch(conf)# interface fastethernet0/1

Switch(conf-if)# switchport backup interface fastethernet0/2 preemption delay 150

Switch(conf-if)# end

This example shows how to configure the Fast Ethernet interface as the MMU primary VLAN:

Switch# configure terminal 

Switch(conf)# interface fastethernet0/1

Switch(conf-if)# switchport backup interface fastethernet0/2 mmu primary vlan 1021

Switch(conf-if)# end

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

The following example shows how to configure preferred VLANs:

Switch(config)# interface gigabitethernet 0/6

Switch(config-if)# switchport backup interface gigabitethernet 0/8 prefer vlan 60,100-120

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

In the following example, VLANs 60, and 100 to 120 are configured on the switch:

Switch(config)# interface gigabitEthernet 0/6

Switch(config-if)# switchport backup interface gigabitEthernet 0/8 prefer vlan 60,100-120

When both interfaces are up, Gi0/6 forwards traffic for VLANs 1 to 50, and Gi0/8 forwards traffic for VLANs 60 and 100 to 120.

Switch# show interfaces switchport backup

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State

------------------------------------------------------------------------

GigabitEthernet0/6    GigabitEthernet0/8    Active Up/Backup Up

Vlans Preferred on Active Interface: 1-50

Vlans Preferred on Backup Interface: 60, 100-120

When a Flex Link interface goes down (LINK_DOWN), VLANs preferred on this interface are moved to the peer interface of the Flex Link pair. In this example, if interface Gi0/6 goes down, Gi0/8 carries all VLANs of the Flex Link pair.

Switch# show interfaces switchport backup

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State

------------------------------------------------------------------------

GigabitEthernet0/6    GigabitEthernet0/8    Active Down/Backup Up

Vlans Preferred on Active Interface: 1-50

Vlans Preferred on Backup Interface: 60, 100-120

When a Flex Link interface comes up, VLANs preferred on this interface are blocked on the peer interface and moved to the forwarding state on the interface that has just come up. In this example, if interface Gi0/6 comes up, VLANs preferred on this interface are blocked on the peer interface Gi0/8 and forwarded on Gi0/6.

Switch# show interfaces switchport backup

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State

------------------------------------------------------------------------

GigabitEthernet0/6    GigabitEthernet0/8    Active Up/Backup Up

Vlans Preferred on Active Interface: 1-50

Vlans Preferred on Backup Interface: 60, 100-120

The following example shows how to configure multicast fast-convergence on interface Gi0/11:

Switch# configure terminal 

Switch(config)# interface gigabitEthernet 0/11

Switch(config-if)# switchport backup interface gigabitEthernet 0/12 multicast 
fast-convergence

Switch(config-if)# end

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

Switch# show interfaces switchport backup detail 

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State

------------------------------------------------------------------------

GigabitEthernet0/11   GigabitEthernet0/12   Active Up/Backup Standby

        Preemption Mode  : off

        Multicast Fast Convergence  : On

        Bandwidth : 1000000 Kbit (Gi0/11), 1000000 Kbit (Gi0/12)

        Mac Address Move Update Vlan : auto

Related Commands

switchport block

Use the switchport block interface configuration command to prevent unknown multicast or unicast packets from being forwarded. Use the no form of this command to allow forwarding unknown multicast or unicast packets.

switchport block {multicast | unicast}

no switchport block {multicast | unicast}

Syntax Description

Defaults

Unknown multicast and unicast traffic is not blocked.

Command Modes

Interface configuration

Command History

Usage Guidelines

By default, all traffic with unknown MAC addresses is sent to all ports. You can block unknown multicast or unicast traffic on protected or nonprotected ports. If unknown multicast or unicast traffic is not blocked on a protected port, there could be security issues.

With multicast traffic, the port blocking feature blocks only pure Layer 2 packets. Multicast packets that contain IPv4 or IPv6 information in the header are not blocked.

If the port is a user network interface (UNI) or enhanced network interface (ENI), you must use the no shutdown interface configuration command to enable it before using the switchport block command. UNIs and ENIs are disabled by default. Network node interfaces (NNIs) are enabled by default.

Blocking unknown multicast or unicast traffic is not automatically enabled on protected ports; you must explicitly configure it.

Note For more information about blocking packets, see the software configuration guide for this release.

Examples

This example shows how to block unknown multicast traffic on an interface:

Switch(config-if)# switchport block multicast

You can verify your setting by entering the show interfaces interface-id switchport privileged EXEC command.

Related Commands

switchport host

Use the switchport host interface configuration command to optimize a Layer 2 port for a host connection. The no form of this command has no affect on the system.

switchport host

Syntax Description

This command has no arguments or keywords.

Defaults

The default is for the port to not be optimized for a host connection.

Command Modes

Interface configuration

Command History

Usage Guidelines

To optimize the port for a host connection, the switchport host command sets switch port mode to access, enables spanning tree Port Fast, and disables channel grouping. Only an end station can accept this configuration.

Because spanning tree Port Fast is enabled, you should enter the switchport host command only on ports that are connected to a single host. Connecting other switches, hubs, concentrators, or bridges to a fast-start port can cause temporary spanning-tree loops.

Enable the switchport host command to decrease the time that it takes to start up packet forwarding.

Examples

This example shows how to optimize the port configuration for a host connection:

Switch(config-if)# switchport host 

switchport mode will be set to access 

spanning-tree portfast will be enabled 

channel group will be disabled 

Switch(config-if)# 

You can verify your setting by entering the show interfaces interface-id switchport privileged EXEC command.

Related Commands

switchport mode

Use the switchport mode interface configuration command to configure the VLAN membership mode of a port. Use the no form of this command to reset the mode to the default.

switchport mode {access | dot1q-tunnel | private-vlan | trunk}

no switchport mode

Syntax Description