To assign an Ethernet port to an EtherChannel group, or to enable an EtherChannel mode, or both, use the channel-group command in interface configuration mode. To remove an Ethernet port from an EtherChannel group, use the no form of this command.

Command Default

No channel groups are assigned.

No mode is configured.

Command Modes

Interface configuration

Usage Guidelines

For Layer 2 EtherChannels, the channel-group command automatically creates the port-channel interface when the channel group gets its first physical port. You do not have to use the interface port-channel command in global configuration mode to manually create a port-channel interface. If you create the port-channel interface first, the channel-group-number can be the same as the port-channel-number, or you can use a new number. If you use a new number, the channel-group command dynamically creates a new port channel.

Although it is not necessary to disable the IP address that is assigned to a physical port that is part of a channel group, we strongly recommend that you do so.

You create Layer 3 port channels by using the interface port-channel command followed by the no switchport interface configuration command. Manually configure the port-channel logical interface before putting the interface into the channel group.

After you configure an EtherChannel, configuration changes that you make on the port-channel interface apply to all the physical ports assigned to the port-channel interface. Configuration changes applied to the physical port affect only the port where you apply the configuration. To change the parameters of all ports in an EtherChannel, apply configuration commands to the port-channel interface, for example, spanning-tree commands or commands to configure a Layer 2 EtherChannel as a trunk.

Active mode places a port into a negotiating state in which the port initiates negotiations with other ports by sending LACP packets. A channel is formed with another port group in either the active or passive mode.

Auto mode places a port into a passive negotiating state in which the port responds to PAgP packets it receives but does not start PAgP packet negotiation. A channel is formed only with another port group in desirable mode. When auto is enabled, silent operation is the default.

Desirable mode places a port into an active negotiating state in which the port starts negotiations with other ports by sending PAgP packets. An EtherChannel is formed with another port group that is in the desirable or auto mode. When desirable is enabled, silent operation is the default.

If you do not specify non-silent with the auto or desirable mode, silent is assumed. The silent mode is used when the switch is connected to a device that is not PAgP-capable and rarely, if ever, sends packets. An example of a silent partner is a file server or a packet analyzer that is not generating traffic. In this case, running PAgP on a physical port prevents that port from ever becoming operational. However, it allows PAgP to operate, to attach the port to a channel group, and to use the port for transmission. Both ends of the link cannot be set to silent.

In on mode, a usable EtherChannel exists only when both connected port groups are in the on mode.

Caution

Use care when using the on mode. This is a manual configuration, and ports on both ends of the EtherChannel must have the same configuration. If the group is misconfigured, packet loss or spanning-tree loops can occur.

Passive mode places a port into a negotiating state in which the port responds to received LACP packets but does not initiate LACP packet negotiation. A channel is formed only with another port group in active mode.

Do not configure an EtherChannel in both the PAgP and LACP modes. EtherChannel groups running PAgP and LACP can coexist on the same switch or on different switches in the stack (but not in a cross-stack configuration). Individual EtherChannel groups can run either PAgP or LACP, but they cannot interoperate.

If you set the protocol by using the channel-protocol interface configuration command, the setting is not overridden by the channel-group interface configuration command.

Do not configure a port that is an active or a not-yet-active member of an EtherChannel as an IEEE 802.1x port. If you try to enable IEEE 802.1x authentication on an EtherChannel port, an error message appears, and IEEE 802.1x authentication is not enabled.

Do not configure a secure port as part of an EtherChannel or configure an EtherChannel port as a secure port.

For a complete list of configuration guidelines, see the “Configuring EtherChannels” chapter in the software configuration guide for this release.

Caution

Do not enable Layer 3 addresses on the physical EtherChannel ports. Do not assign bridge groups on the physical EtherChannel ports because it creates loops.

To restrict the protocol used on a port to manage channeling, use the channel-protocol command in interface configuration mode. To return to the default setting, use the no form of this command.

Command Default

No protocol is assigned to the EtherChannel.

Command Modes

Interface configuration

Usage Guidelines

Use the channel-protocol command only to restrict a channel to LACP or PAgP. If you set the protocol by using the channel-protocol command, the setting is not overridden by the channel-group interface configuration command.

You must use the channel-group interface configuration command to configure the EtherChannel parameters. The channel-group command also can set the mode for the EtherChannel.

You cannot enable both the PAgP and LACP modes on an EtherChannel group.

PAgP and LACP are not compatible; both ends of a channel must use the same protocol.

You cannot configure PAgP on cross-stack configurations.

To clear Link Aggregation Control Protocol (LACP) channel-group counters, use the clear lacp command in privileged EXEC mode.

Command Default

None

Command Modes

Privileged EXEC

Usage Guidelines

You can clear all counters by using the clear lacp counters command, or you can clear only the counters for the specified channel group by using the clear lacp channel-group-number counters command.

To clear the Port Aggregation Protocol (PAgP) channel-group information, use the clear pagp command in privileged EXEC mode.

Command Default

None

Command Modes

Privileged EXEC

Usage Guidelines

You can clear all counters by using the clear pagp counters command, or you can clear only the counters for the specified channel group by using the clear pagp channel-group-number counters command.

To clear the spanning-tree counters, use the clear spanning-tree counters command in privileged EXEC mode.

Command Default

None

Command Modes

Privileged EXEC

Usage Guidelines

If the interface-id value is not specified, spanning-tree counters are cleared for all interfaces.

To restart the protocol migration process and force renegotiation with neighboring switches on the interface, use the clear spanning-tree detected-protocols command in privileged EXEC mode.

Command Default

None

Command Modes

Privileged EXEC

Usage Guidelines

A switch running the rapid per-VLAN spanning-tree plus (rapid-PVST+) protocol or the Multiple Spanning Tree Protocol (MSTP) supports a built-in protocol migration method that enables it to interoperate with legacy IEEE 802.1D switches. If a rapid-PVST+ or an MSTP switch receives a legacy IEEE 802.1D configuration bridge protocol data unit (BPDU) with the protocol version set to 0, the switch sends only IEEE 802.1D BPDUs on that port. A multiple spanning-tree (MST) switch can also detect that a port is at the boundary of a region when it receives a legacy BPDU, an MST BPDU (Version 3) associated with a different region, or a rapid spanning-tree (RST) BPDU (Version 2).

The switch does not automatically revert to the rapid-PVST+ or the MSTP mode if it no longer receives IEEE 802.1D BPDUs because it cannot learn whether the legacy switch has been removed from the link unless the legacy switch is the designated switch. Use the clear spanning-tree detected-protocols command in this situation.

To enable debugging of EtherChannels, use the debug etherchannel command in privileged EXEC mode. To disable debugging, use the no form of the command.

Command Default

Debugging is disabled.

Command Modes

Privileged EXEC

Usage Guidelines

The undebug etherchannel command is the same as the no debug etherchannel command.

Note	Although the linecard keyword is displayed in the command-line help, it is not supported.

When you enable debugging on a stack, it is enabled only on the active switch. To enable debugging on the standby switch , start a session from the active switch by using the session switch-number command in privileged EXEC mode. Enter the debug command at the command-line prompt of the standby switch.

To enable debugging on the standby switch without first starting a session on the active switch, use the remote command switch-number LINE command in privileged EXEC mode.

To enable debugging of Link Aggregation Control Protocol (LACP) activity, use the debug lacp command in privileged EXEC mode. To disable LACP debugging, use the no form of this command.

Command Default

Debugging is disabled.

Command Modes

Privileged EXEC

Usage Guidelines

The undebug etherchannel command is the same as the no debug etherchannel command.

When you enable debugging on a stack, it is enabled only on the active switch. To enable debugging on the standby switch , start a session from the active switch by using the session switch-number command in privileged EXEC mode. Enter the debug command at the command-line prompt of the standby switch.

To enable debugging on the standby switch without first starting a session on the active switch, use the remote command switch-number LINE command in privileged EXEC mode.

To enable debugging of Port Aggregation Protocol (PAgP) activity, use the debug pagp command in privileged EXEC mode. To disable PAgP debugging, use the no form of this command.

Command Default

Debugging is disabled.

Command Modes

Privileged EXEC

Usage Guidelines

The undebug pagp command is the same as the no debug pagp command.

When you enable debugging on a stack, it is enabled only on the active switch. To enable debugging on the standby switch , start a session from the active switch by using the session switch-number command in privileged EXEC mode. Enter the debug command at the command-line prompt of the standby switch.

To enable debugging on the standby switch without first starting a session on the active switch, use the remote command switch-number LINE command in privileged EXEC mode.

To enable debugging of the platform-dependent port manager software module, use the debug platform pm command in privileged EXEC mode. To disable debugging, use the no form of this command.

Syntax Description

Command Default

Debugging is disabled.

Command Modes

Privileged EXEC

Usage Guidelines

The undebug platform pm command is the same as the no debug platform pm command.

When you enable debugging on a stack, it is enabled only on the active switch. To enable debugging on the standby switch , start a session from the active switch by using the session switch-number command in privileged EXEC mode. Enter the debug command at the command-line prompt of the standby switch.

To enable debugging on the standby switch without first starting a session on the active switch, use the remote command switch-number LINE command in privileged EXEC mode.

To enable debugging of the platform-dependent UniDirectional Link Detection (UDLD) software, use the debug platform udld command in privileged EXEC mode. To disable debugging, use the no form of this command.

Command Default

Debugging is disabled.

Command Modes

Privileged EXEC

Usage Guidelines

The undebug platform udld command is the same as the no debug platform udld command.

When you enable debugging on a switch stack, it is enabled only on the active switch. To enable debugging on a stack member, you can start a session from the active switch by using the session switch-number EXEC command. Then enter the debug command at the command-line prompt of the stack member.

To enable debugging of spanning-tree activities, use the debug spanning-tree command in EXEC mode. To disable debugging, use the no form of this command.

Syntax Description

Command Default

Debugging is disabled.

Command Modes

Privileged EXEC

Usage Guidelines

The undebug spanning-tree command is the same as the no debug spanning-tree command.

When you enable debugging on a stack, it is enabled only on the active switch. To enable debugging on the standby switch , start a session from the active switch by using the session switch-number command in privileged EXEC mode. Enter the debug command at the command-line prompt of the standby switch.

To enable debugging on the standby switch without first starting a session on the active switch, use the remote command switch-number LINE command in privileged EXEC mode.

To access or create a port channel, use the interface port-channel command in global configuration mode. Use the no form of this command to remove the port channel.

Command Default

No port channel logical interfaces are defined.

Command Modes

Global configuration

Usage Guidelines

For Layer 2 EtherChannels, you do not have to create a port-channel interface before assigning physical ports to a channel group. Instead, you can use the channel-group interface configuration command, which automatically creates the port-channel interface when the channel group obtains its first physical port. If you create the port-channel interface first, the channel-group-number can be the same as the port-channel-number, or you can use a new number. If you use a new number, the channel-group command dynamically creates a new port channel.

You create Layer 3 port channels by using the interface port-channel command followed by the no switchport interface configuration command. You should manually configure the port-channel logical interface before putting the interface into the channel group.

Only one port channel in a channel group is allowed.

Caution

When using a port-channel interface as a routed port, do not assign Layer 3 addresses on the physical ports that are assigned to the channel group.

Caution

Do not assign bridge groups on the physical ports in a channel group used as a Layer 3 port channel interface because it creates loops. You must also disable spanning tree.

Follow these guidelines when you use the interface port-channel command:

• If you want to use the Cisco Discovery Protocol (CDP), you must configure it on the physical port and not on the port channel interface.

• Do not configure a port that is an active member of an EtherChannel as an IEEE 802.1x port. If IEEE 802.1x is enabled on a not-yet active port of an EtherChannel, the port does not join the EtherChannel.

For a complete list of configuration guidelines, see the “Configuring EtherChannels” chapter in the software configuration guide for this release.

To define the maximum number of active LACP ports allowed in a port channel, use the lacp max-bundle command in interface configuration mode. To return to the default setting, use the no form of this command.

Command Default

None

Command Modes

Interface configuration

Usage Guidelines

An LACP channel group can have up to 16 Ethernet ports of the same type. Up to eight ports can be active, and up to eight ports can be in hot-standby mode. When there are more than eight ports in an LACP channel group, the switch on the controlling end of the link uses port priorities to determine which ports are bundled into the channel and which ports are put in hot-standby mode. Port priorities on the other switch (the noncontrolling end of the link) are ignored.

The lacp max-bundle command must specify a number greater than the number specified by the port-channel min-links command.

Use the show etherchannel summary privileged EXEC command to see which ports are in the hot-standby mode (denoted with an H port-state flag in the output display).

To configure the port priority for the Link Aggregation Control Protocol (LACP), use the lacp port-priority command in interface configuration mode. To return to the default setting, use the no form of this command.

Command Default

The default is 32768.

Command Modes

Interface configuration

Usage Guidelines

The lacp port-priority interface configuration command determines which ports are bundled and which ports are put in hot-standby mode when there are more than eight ports in an LACP channel group.

An LACP channel group can have up to 16 Ethernet ports of the same type. Up to eight ports can be active, and up to eight ports can be in standby mode.

In port-priority comparisons, a numerically lower value has a higher priority: When there are more than eight ports in an LACP channel group, the eight ports with the numerically lowest values (highest priority values) for LACP port priority are bundled into the channel group, and the lower-priority ports are put in hot-standby mode. If two or more ports have the same LACP port priority (for example, they are configured with the default setting of 65535), then an internal value for the port number determines the priority.

Note	The LACP port priorities are only effective if the ports are on the switch that controls the LACP link. See the lacp system-priority global configuration command for determining which switch controls the link.

Use the show lacp internal privileged EXEC command to display LACP port priorities and internal port number values.

For information about configuring LACP on physical ports, see the configuration guide for this release.

To configure the system priority for the Link Aggregation Control Protocol (LACP), use the lacp system-priority command in global configuration mode on the switch. To return to the default setting, use the no form of this command.

Command Default

The default is 32768.

Command Modes

Global configuration

Usage Guidelines

The lacp system-priority command determines which switch in an LACP link controls port priorities.

An LACP channel group can have up to 16 Ethernet ports of the same type. Up to eight ports can be active, and up to eight ports can be in standby mode. When there are more than eight ports in an LACP channel group, the switch on the controlling end of the link uses port priorities to determine which ports are bundled into the channel and which ports are put in hot-standby mode. Port priorities on the other switch (the noncontrolling end of the link) are ignored.

In priority comparisons, numerically lower values have a higher priority. Therefore, the system with the numerically lower value (higher priority value) for LACP system priority becomes the controlling system. If both switches have the same LACP system priority (for example, they are both configured with the default setting of 32768), the LACP system ID (the switch MAC address) determines which switch is in control.

The lacp system-priority command applies to all LACP EtherChannels on the switch.

Use the show etherchannel summary privileged EXEC command to see which ports are in the hot-standby mode (denoted with an H port-state flag in the output display).

To learn the source address of incoming packets received from an EtherChannel port, use the pagp learn-method command in interface configuration mode. To return to the default setting, use the no form of this command.

Command Default

The default is aggregation-port (logical port channel).

Command Modes

Interface configuration

Usage Guidelines

The learn method must be configured the same at both ends of the link.

The switch supports address learning only on aggregate ports even though the physical-port keyword is provided in the command-line interface (CLI). The pagp learn-method and the pagp port-priority interface configuration commands have no effect on the switch hardware, but they are required for PAgP interoperability with devices that only support address learning by physical ports.

When the link partner to the switch is a physical learner, we recommend that you configure the switch as a physical-port learner by using the pagp learn-method physical-port interface configuration command. We also recommend that you set the load-distribution method based on the source MAC address by using the port-channel load-balance src-mac global configuration command. Use the pagp learn-method interface configuration command only in this situation.

To select a port over which all Port Aggregation Protocol (PAgP) traffic through the EtherChannel is sent, use the pagp port-priority command in interface configuration mode. If all unused ports in the EtherChannel are in hot-standby mode, they can be placed into operation if the currently selected port and link fails. To return to the default setting, use the no form of this command.

Command Default

The default is 128.

Command Modes

Interface configuration

Usage Guidelines

The physical port with the highest priority that is operational and has membership in the same EtherChannel is the one selected for PAgP transmission.

The switch supports address learning only on aggregate ports even though the physical-port keyword is provided in the command-line interface (CLI). The pagp learn-method and the pagp port-priority interface configuration commands have no effect on the switch hardware, but they are required for PAgP interoperability with devices that only support address learning by physical ports, such as the Catalyst 1900 switch.

When the link partner to the switch is a physical learner, we recommend that you configure the switch as a physical-port learner by using the pagp learn-method physical-port interface configuration command. We also recommend that you set the load-distribution method based on the source MAC address by using the port-channel load-balance src-mac global configuration command. Use the pagp learn-method interface configuration command only in this situation.

To set the load-distribution method among the ports in the EtherChannel, use the port-channel load-balance command in global configuration mode. To reset the load-balancing mechanism to the default setting, use the no form of this command.

Command Default

The default is src-mac.

Command Modes

Global configuration

Usage Guidelines

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

To set combinations of load-distribution methods among the ports in the EtherChannel, use the port-channel load-balance extended command in global configuration mode. To reset the extended load-balancing mechanism to the default setting, use the no form of this command.

Command Default

The default is src-mac.

Command Modes

Global configuration

Usage Guidelines

For information about when to use these forwarding methods, see the Layer 2/3 Configuration Guide (Catalyst 3650 Switches) for this release.

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

To define the minimum number of LACP ports that must be bundled in the link-up state and bundled in the EtherChannel in order that a port channel becomes active, use the port-channel min-links command in interface configuration mode. To return to the default setting, use the no form of this command.

Command Default

None

Command Modes

Interface configuration

Usage Guidelines

An LACP channel group can have up to 16 Ethernet ports of the same type. Up to eight ports can be active, and up to eight ports can be in hot-standby mode. When there are more than eight ports in an LACP channel group, the switch on the controlling end of the link uses port priorities to determine which ports are bundled into the channel and which ports are put in hot-standby mode. Port priorities on the other switch (the noncontrolling end of the link) are ignored.

The port-channel min-links command must specify a number a less than the number specified by the lacp max-bundle command.

Use the show etherchannel summary privileged EXEC command to see which ports are in the hot-standby mode (denoted with an H port-state flag in the output display).

To display EtherChannel information for a channel, use the show etherchannel command in user EXEC mode.

Command Default

None

Command Modes

User EXEC

Usage Guidelines

If you do not specify a channel group number, all channel groups are displayed.

In the output, the passive port list field is displayed only for Layer 3 port channels. This field means that the physical port, which is still not up, is configured to be in the channel group (and indirectly is in the only port channel in the channel group).

To display Link Aggregation Control Protocol (LACP) channel-group information, use the show lacp command in user EXEC mode.

Command Default

None

Command Modes

User EXEC

Usage Guidelines

You can enter any show lacp command to display the active channel-group information. To display specific channel information, enter the show lacp command with a channel-group number.

If you do not specify a channel group, information for all channel groups appears.

You can enter the channel-group-number to specify a channel group for all keywords except sys-id.

To display Port Aggregation Protocol (PAgP) channel-group information, use the show pagp command in EXEC mode.

Command Default

None

Command Modes

User EXEC

Privileged EXEC

Usage Guidelines

You can enter any show pagp command to display the active channel-group information. To display the nonactive information, enter the show pagp command with a channel-group number.

To display platform-dependent EtherChannel information, use the show platform etherchannel command in privileged EXEC mode.

Command Default

None

Command Modes

Privileged EXEC

Usage Guidelines

Use this command only when you are working directly with a technical support representative while troubleshooting a problem.

Do not use this command unless a technical support representative asks you to do so.

To display platform-dependent port manager information, use the show platform pm command in privileged EXEC mode.

Command Default

None

Command Modes

Privileged EXEC

Usage Guidelines

Use this command only when you are working directly with your technical support representative while troubleshooting a problem.

Do not use this command unless your technical support representative asks you to do so.

To display UniDirectional Link Detection (UDLD) administrative and operational status for all ports or the specified port, use the show udld command in user EXEC mode.

Command Default

None

Command Modes

User EXEC

Usage Guidelines

If you do not enter an interface ID, administrative and operational UDLD status for all interfaces appear.

To put an interface that is in Layer 3 mode into Layer 2 mode for Layer 2 configuration, use the switchport command in interface configuration mode. To put an interface in Layer 3 mode, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

By default, all interfaces are in Layer 2 mode.

Command Modes

Interface configuration

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 use this command before assigning an IP address to a routed port.

Note	This command is not supported on switches running the LAN Base feature set.

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

When you put an interface that is in Layer 2 mode into Layer 3 mode (or the reverse), the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.

Note	If an interface is configured as a Layer 3 interface, you must first enter the switchport command to configure the interface as a Layer 2 port. Then you can enter the switchport access vlan and switchport mode commands.

The switchport command is not used on platforms that do not support Cisco-routed ports. All physical ports on such platforms are assumed to be Layer 2-switched interfaces.

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

To configure a port as a static-access port, use the switchport access vlan command in interface configuration mode. To reset the access mode to the default VLAN mode for the switch, use the no form of this command.

Command Default

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

Command Modes

Interface configuration

Usage Guidelines

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

If the switchport mode is set to access vlan vlan-id, the port operates as a member of the specified VLAN. An access port can be assigned to only one VLAN.

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

To configure the VLAN membership mode of a port, use the switchport mode command in interface configuration mode. To reset the mode to the appropriate default for the device, use the no form of this command.

Command Default

The default mode is dynamic auto.

Command Modes

Interface configuration

Usage Guidelines

Note	Although visible in the CLI, the dot1q-tunnel keyword is not supported.

A configuration that uses the access,or trunk keywords takes effect only when you configure the port in the appropriate mode by using the switchport mode command. The static-access and trunk configuration are saved, but only one configuration is active at a time.

When you enter access mode, the interface changes to permanent nontrunking mode and negotiates to convert the link into a nontrunk link even if the neighboring interface does not agree to the change.

When you enter trunk mode, the interface changes to permanent trunking mode and negotiates to convert the link into a trunk link even if the interface connecting to it does not agree to the change.

When you enter dynamic auto mode, the interface converts the link to a trunk link if the neighboring interface is set to trunk or desirable mode.

When you enter dynamic desirable mode, the interface becomes a trunk interface if the neighboring interface is set to trunk, desirable, or auto mode.

To autonegotiate trunking, the interfaces must be in the same VLAN Trunking Protocol (VTP) domain. Trunk negotiation is managed by the Dynamic Trunking Protocol (DTP), which is a point-to-point protocol. However, some internetworking devices might forward DTP frames improperly, which could cause misconfigurations. To avoid this problem, configure interfaces connected to devices that do not support DTP to not forward DTP frames, which turns off DTP.

• If you do not intend to trunk across those links, use the switchport mode access interface configuration command to disable trunking.
• To enable trunking to a device that does not support DTP, use the switchport mode trunk and switchport nonegotiate interface configuration commands to cause the interface to become a trunk but to not generate DTP frames.

Access ports and trunk ports are mutually exclusive.

The IEEE 802.1x feature interacts with switchport modes in these ways:

• If you try to enable IEEE 802.1x on a trunk port, an error message appears, and IEEE 802.1x is not enabled. If you try to change the mode of an IEEE 802.1x-enabled port to trunk, the port mode is not changed.
• If you try to enable IEEE 802.1x on a port set to dynamic auto or dynamic desirable, an error message appears, and IEEE 802.1x is not enabled. If you try to change the mode of an IEEE 802.1x-enabled port to dynamic auto or dynamic desirable, the port mode is not changed.
• If you try to enable IEEE 802.1x on a dynamic-access (VLAN Query Protocol [VQP]) port, an error message appears, and IEEE 802.1x is not enabled. If you try to change an IEEE 802.1x-enabled port to dynamic VLAN assignment, an error message appears, and the VLAN configuration is not changed.

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

To specify that Dynamic Trunking Protocol (DTP) negotiation packets are not sent on the Layer 2 interface, use the switchport nonegotiate command in interface configuration mode. Use the no form of this command to return to the default setting.

Syntax Description

This command has no arguments or keywords.

Command Default

The default is to use DTP negotiation to learn the trunking status.

Command Modes

Interface configuration

Usage Guidelines

The no switchport nonegotiate command removes nonegotiate status.

This command is valid only when the interface switchport mode is access or trunk (configured by using the switchport mode access or the switchport mode trunk interface configuration command). This command returns an error if you attempt to execute it in dynamic (auto or desirable) mode.

Internetworking devices that do not support DTP might forward DTP frames improperly and cause misconfigurations. To avoid this problem, turn off DTP by using the switchport nonegotiate command to configure the interfaces connected to devices that do not support DTP to not forward DTP frames.

When you enter the switchport nonegotiate command, DTP negotiation packets are not sent on the interface. The device does or does not trunk according to the mode parameter: access or trunk.

• If you do not intend to trunk across those links, use the switchport mode access interface configuration command to disable trunking.

• To enable trunking on a device that does not support DTP, use the switchport mode trunk and switchport nonegotiate interface configuration commands to cause the interface to become a trunk but to not generate DTP frames.

To enable aggressive or normal mode in the UniDirectional Link Detection (UDLD) and to set the configurable message timer time, use the udld command in global configuration mode. To disable aggressive or normal mode UDLD on all fiber-optic ports, use the no form of the command.

Command Default

UDLD is disabled on all interfaces.

The message timer is set at 15 seconds.

Command Modes

Global configuration

Usage Guidelines

UDLD supports two modes of operation: normal (the default) and aggressive. In normal mode, UDLD detects unidirectional links due to misconnected interfaces on fiber-optic connections. In aggressive mode, UDLD also detects unidirectional links due to one-way traffic on fiber-optic and twisted-pair links and due to misconnected interfaces on fiber-optic links. For information about normal and aggressive modes, see the Catalyst 2960-X Switch Layer 2 Configuration GuideCatalyst 2960-XR Switch Layer 2 Configuration GuideLayer 2/3 Configuration Guide (Catalyst 3650 Switches).

If you change the message time between probe packets, you are making a compromise between the detection speed and the CPU load. By decreasing the time, you can make the detection-response faster but increase the load on the CPU.

This command affects fiber-optic interfaces only. Use the udld interface configuration command to enable UDLD on other interface types.

You can use these commands to reset an interface shut down by UDLD:

• The udld reset privileged EXEC command to reset all interfaces shut down by UDLD.

• The shutdown and no shutdown interface configuration commands.

• The no udld enable global configuration command followed by the udld {aggressive | enable} global configuration command to reenable UDLD globally.

• The no udld port interface configuration command followed by the udld port or udld port aggressive interface configuration command to reenable UDLD on the specified interface.

• The errdisable recovery cause udld and errdisable recovery interval interval global configuration commands to automatically recover from the UDLD error-disabled state.

To enable UniDirectional Link Detection (UDLD) on an individual interface or to prevent a fiber-optic interface from being enabled by the udld global configuration command, use the udld port command in interface configuration mode. To return to the udld global configuration command setting or to disable UDLD if entered for a nonfiber-optic port, use the no form of this command.

Command Default

On fiber-optic interfaces, UDLD is disabled and fiber-optic interfaces enable UDLD according to the state of the udld enable or udld aggressive global configuration command.

On nonfiber-optic interfaces, UDLD is disabled.

Command Modes

Interface configuration

Usage Guidelines

A UDLD-capable port cannot detect a unidirectional link if it is connected to a UDLD-incapable port of another switch.

UDLD supports two modes of operation: normal (the default) and aggressive. In normal mode, UDLD detects unidirectional links due to misconnected interfaces on fiber-optic connections. In aggressive mode, UDLD also detects unidirectional links due to one-way traffic on fiber-optic and twisted-pair links and due to misconnected interfaces on fiber-optic links.

To enable UDLD in normal mode, use the udld port interface configuration command. To enable UDLD in aggressive mode, use the udld port aggressive interface configuration command.

Use the no udld port command on fiber-optic ports to return control of UDLD to the udld enable global configuration command or to disable UDLD on nonfiber-optic ports.

Use the udld port aggressive command on fiber-optic ports to override the setting of the udld enable or udld aggressive global configuration command. Use the no form on fiber-optic ports to remove this setting and to return control of UDLD enabling to the udld global configuration command or to disable UDLD on nonfiber-optic ports.

You can use these commands to reset an interface shut down by UDLD:

• The udld reset privileged EXEC command resets all interfaces shut down by UDLD.

• The shutdown and no shutdown interface configuration commands.

• The no udld enable global configuration command, followed by the udld {aggressive | enable} global configuration command reenables UDLD globally.

• The no udld port interface configuration command, followed by the udld port or udld port aggressive interface configuration command reenables UDLD on the specified interface.

• The errdisable recovery cause udld and errdisable recovery interval interval global configuration commands automatically recover from the UDLD error-disabled state.

To reset all interfaces disabled by UniDirectional Link Detection (UDLD) and permit traffic to begin passing through them again (though other features, such as spanning tree, Port Aggregation Protocol (PAgP), and Dynamic Trunking Protocol (DTP) still have their normal effects, if enabled), use the udld reset command in privileged EXEC mode.

Syntax Description

This command has no arguments or keywords.

Command Default

None

Command Modes

Privileged EXEC

Usage Guidelines

If the interface configuration is still enabled for UDLD, these ports begin to run UDLD again and are disabled for the same reason if the problem has not been corrected.