Configuring Layer 2 Interfaces

This chapter describes how to configure Layer 2 switching ports as access or trunk ports on Cisco NX-OS devices.


Note

A Layer 2 port can function as either one of the following:

  • A trunk port

  • An access port


Note

See the Cisco Nexus 9000 Series NX-OS System Management Configuration Guide for information about configuring a SPAN destination interface.

You can configure Layer 2 switching ports as access or trunk ports. Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network. All Layer 2 switching ports maintain media access control (MAC) address tables.


Note

See the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for information about VLANs, MAC address tables, private VLANs, and the Spanning Tree Protocol.

Information About Access and Trunk Interfaces


Note

See the Cisco Nexus 9000 Series NX-OS High Availability and Redundancy Guide for complete information on high-availability features.


Note

The device supports only IEEE 802.1Q-type VLAN trunk encapsulation.

About Access and Trunk Interfaces

A Layer 2 port can be configured as an access or a trunk port as follows:

  • An access port can have only one VLAN configured on that port; it can carry traffic for only one VLAN.

  • A trunk port can have two or more VLANs configured on that port; it can carry traffic for several VLANs simultaneously.

By default, all ports on the device are Layer 3 ports.

You can make all ports Layer 2 ports using the setup script or by entering the system default switchport command. See the Cisco Nexus 9000 Series NX-OS Fundamentals Configuration Guide for information about using the setup script. To configure the port as a Layer 2 port using the CLI, use the switchport command.

All ports in the same trunk must be in the same VDC, and trunk ports cannot carry VLANs from different VDCs.

The following figure shows how you can use trunk ports in the network. The trunk port carries traffic for two or more VLANs.

Figure 1. Trunk and Access Ports and VLAN Traffic




Note

See the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for information about VLANs.

In order to correctly deliver the traffic on a trunk port with several VLANs, the device uses the IEEE 802.1Q encapsulation, or tagging, method (see the “IEEE 802.1Q Encapsulation” section for more information).


Note

See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for information about subinterfaces on Layer 3 interfaces.

To optimize the performance on access ports, you can configure the port as a host port. Once the port is configured as a host port, it is automatically set as an access port, and channel grouping is disabled. Use the host designation to decrease the time that it takes the designated port to begin to forward packets.

Only an end station can be set as a host port; you will receive an error message if you attempt to configure other ports as hosts.

If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address.

A Layer 2 interface can function as either an access port or a trunk port; it cannot function as both port types simultaneously.

When you change a Layer 2 interface back to a Layer 3 interface, that interface loses all the Layer 2 configuration and resumes the default VLAN configurations.

IEEE 802.1Q Encapsulation


Note

For information about VLANs, see the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide.

A trunk is a point-to-point link between the switch and another networking device. Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network.

To correctly deliver the traffic on a trunk port with several VLANs, the device uses the IEEE 802.1Q encapsulation, or tagging, method that uses a tag that is inserted into the frame header. This tag carries information about the specific VLAN to which the frame and packet belong. This method allows packets that are encapsulated for several different VLANs to traverse the same port and maintain traffic separation between the VLANs. Also, the encapsulated VLAN tag allows the trunk to move traffic end-to-end through the network on the same VLAN.

Figure 2. Header Without and With 802.1Q Tag



Access VLANs

When you configure a port in access mode, you can specify which VLAN will carry the traffic for that interface. If you do not configure the VLAN for a port in access mode, or an access port, the interface carries traffic for the default VLAN (VLAN1).

You can change the access port membership in a VLAN by specifying the new VLAN. You must create the VLAN before you can assign it as an access VLAN for an access port. If you change the access VLAN on an access port to a VLAN that is not yet created, the system shuts that access port down.

If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address.

Native VLAN IDs for Trunk Ports

A trunk port can carry nontagged packets simultaneously with the 802.1Q tagged packets. When you assign a default port VLAN ID to the trunk port, all untagged traffic travels on the default port VLAN ID for the trunk port, and all untagged traffic is assumed to belong to this VLAN. This VLAN is referred to as the native VLAN ID for a trunk port. That is, the native VLAN ID is the VLAN that carries untagged traffic on trunk ports.


Note

Native VLAN ID numbers must match on both ends of the trunk.

The trunk port sends an egressing packet with a VLAN that is equal to the default port VLAN ID as untagged; all the other egressing packets are tagged by the trunk port. If you do not configure a native VLAN ID, the trunk port uses the default VLAN.


Note

You cannot use a Fibre Channel over Ethernet (FCoE) VLAN as a native VLAN for an Ethernet trunk switchport.

Tagging Native VLAN Traffic

The Cisco software supports the IEEE 802.1Q standard on trunk ports. In order to pass untagged traffic through the trunk ports, you must create a VLAN that does not tag any packets (or you can use the default VLAN). Untagged packets can pass through trunk ports and access ports.

However, all packets that enter the device with an 802.1Q tag that matches the value of the native VLAN on the trunk are stripped of any tagging and egress the trunk port as untagged packets. This situation can cause problems because you may want to retain the tagging on packets on the native VLAN for the trunk port.

You can configure the device to drop all untagged packets on the trunk ports and to retain the tagging of packets entering the device with 802.1Q values that are equal to that of the native VLAN ID. All control traffic still passes on the native VLAN. This configuration is global; trunk ports on the device either do or do not retain the tagging for the native VLAN.

Allowed VLANs

By default, a trunk port sends traffic to and receives traffic from all VLANs. All VLAN IDs are allowed on each trunk. However, you can remove VLANs from this inclusive list to prevent traffic from the specified VLANs from passing over the trunk. Later, you can add any specific VLANs that you may want the trunk to carry traffic for back to the list.

To partition the Spanning Tree Protocol (STP) topology for the default VLAN, you can remove VLAN1 from the list of allowed VLANs. Otherwise, VLAN1, which is enabled on all ports by default, will have a very big STP topology, which can result in problems during STP convergence. When you remove VLAN1, all data traffic for VLAN1 on this port is blocked, but the control traffic continues to move on the port.


Note

See the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for more information about STP.


Note

You can change the block of VLANs reserved for internal use. See the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for more information about changing the reserved VLANs.

Default Interfaces

You can use the default interface feature to clear the configured parameters for both physical and logical interfaces such as the Ethernet, loopback, VLAN network, tunnel, and the port-channel interface.


Note

A maximum of eight ports can be selected for the default interface. The default interfaces feature is not supported for management interfaces because the device could go to an unreachable state.

Switch Virtual Interface and Autostate Behavior

In Cisco NX-OS, a switch virtual interface (SVI) represents a logical interface between the bridging function and the routing function of a VLAN in the device.

The operational state of this interface is governed by the state of the various ports in its corresponding VLAN. An SVI interface on a VLAN comes up when at least one port in that VLAN is in the Spanning Tree Protocol (STP) forwarding state. Similarly, this interface goes down when the last STP forwarding port goes down or goes to another STP state.

SVI Autostate Exclude

Typically, when a VLAN interface has multiple ports in the VLAN, the SVI goes to the down state when all the ports in the VLAN go down. You can use the SVI autostate exclude feature to exclude specific ports and port channels while defining the status of the SVI (up or down) even if it belongs to the same VLAN. For example, even if the excluded port or port channel is in the up state and other ports are in the down state in the VLAN, the SVI state is changed to down.


Note

You can use the SVI autostate exclude feature only for switched physical Ethernet ports and port channels.

SVI Autostate Disable

You can also use the SVI for inband management of a device. Specifically, you can configure the autostate disable feature to keep an SVI up even if no interface is up in the corresponding VLAN. You can configure this feature for the system (for all SVIs) or for an individual SVI.

High Availability

The software supports high availability for Layer 2 ports.


Note

See the Cisco Nexus 9000 Series NX-OS High Availability and Redundancy Guide for complete information about high availability features.

Virtualization Support

All ports in the same trunk must be in the same VDC, and trunk ports cannot carry VLANs from different VDCs.

Licensing Requirements for Layer 2 Port Modes

The following table shows the licensing requirements for this feature:

Product

License Requirement

Cisco NX-OS

Layer 2 port modes require no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you.

Prerequisites for Layer 2 Interfaces

Layer 2 interfaces have the following prerequisites:

  • You are logged onto the device.

  • You must configure the port as a Layer 2 port before you can use the switchport mode command. By default, all ports on the device are Layer 3 ports. By default, all ports on the Cisco Nexus 9504 and Cisco Nexus 9508 devices are Layer 2 ports.

Guidelines and Limitations for Layer 2 Interfaces

VLAN trunking has the following configuration guidelines and limitations:

  • A port can be either a Layer 2 or a Layer 3 interface; it cannot be both simultaneously.

  • When you change a Layer 3 port to a Layer 2 port or a Layer 2 port to a Layer 3 port, all layer-dependent configuration is lost. When you change an access or trunk port to a Layer 3 port, all information about the access VLAN, native VLAN, allowed VLANs, and so forth, is lost.

  • Do not connect devices with access links because access links may partition a VLAN.

  • When connecting Cisco devices through an 802.1Q trunk, make sure that the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning tree loops might result.

  • Disabling spanning tree on the native VLAN of an 802.1Q trunk without disabling spanning tree on every VLAN in the network can cause spanning tree loops. You must leave spanning tree enabled on the native VLAN of an 802.1Q trunk. If you cannot leave spanning tree enabled, you must disable spanning tree on every VLAN in the network. Make sure that your network has no physical loops before you disable spanning tree.

  • When you connect two Cisco devices through 802.1Q trunks, the devices exchange spanning tree bridge protocol data units (BPDUs) on each VLAN allowed on the trunks. The BPDUs on the native VLAN of the trunk are sent untagged to the reserved IEEE 802.1D spanning tree multicast MAC address (01-80-C2-00-00-00). The BPDUs on all other VLANs on the trunk are sent tagged to the reserved Cisco Shared Spanning Tree (SSTP) multicast MAC address (01-00-0c-cc-cc-cd).

  • Non-Cisco 802.1Q devices maintain only a single instance of spanning tree (the Mono Spanning Tree) that defines the spanning tree topology for all VLANs. When you connect a Cisco switch to a non-Cisco switch through an 802.1Q trunk, the Mono Spanning Tree of the non-Cisco switch and the native VLAN spanning tree of the Cisco switch combine to form a single spanning tree topology known as the Common Spanning Tree (CST).

  • Because Cisco devices transmit BPDUs to the SSTP multicast MAC address on VLANs other than the native VLAN of the trunk, non-Cisco devices do not recognize these frames as BPDUs and flood them on all ports in the corresponding VLAN. Other Cisco devices connected to the non-Cisco 802.1Q cloud receive these flooded BPDUs. This BPDU reception allows Cisco switches to maintain a per-VLAN spanning tree topology across a cloud of non-Cisco 802.1Q devices. The non-Cisco 802.1Q cloud that separates the Cisco devices is treated as a single broadcast segment between all devices connected to the non-Cisco 802.1Q cloud through 802.1Q trunks.

  • Make certain that the native VLAN is the same on all of the 802.1Q trunks that connect the Cisco devices to the non-Cisco 802.1Q cloud.

  • If you are connecting multiple Cisco devices to a non-Cisco 802.1Q cloud, all of the connections must be through 802.1Q trunks. You cannot connect Cisco devices to a non-Cisco 802.1Q cloud through access ports because doing so places the access port on the Cisco device into the spanning tree “port inconsistent” state and no traffic will pass through the port.

  • You can group trunk ports into port-channel groups, but all trunks in the group must have the same configuration. When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, the device propagates that setting to all ports in the group, such as the allowed VLANs and the trunk status. For example, if one port in a port group ceases to be a trunk, all ports cease to be trunks.

  • If you try to enable 802.1X on a trunk port, an error message appears, and 802.1X is not enabled. If you try to change the mode of an 802.1X-enabled port to trunk, the port mode is not changed.

  • Only ingress unicast packet counters are supported for SVI counters.

  • When MAC addresses are cleared on a VLAN with the clear mac address-table dynamic command, the dynamic ARP (Address Resolution Protocol) entries on that VLAN are refreshed.

  • If a static ARP entry exists on the VLAN and no MAC address to port mapping is present, the supervisor may generate an ARP request to learn the MAC address. Upon learning the MAC address, the adjacency entry points to the correct physical port.

  • Cisco NX-OS does not support transparent bridging between two VLANs when one of the SVIs is on the Cisco Nexus 9000 using the BIA MAC (burned-in MAC address). This occurs when the BIA MAC is shared between SVIs/VLANs.

    A MAC, different from the BIA MAC, can be configured under the SVI for transparent bridging to work properly.

Default Settings for Layer 2 Interfaces

The following table lists the default settings for device access and trunk port mode parameters.

Table 1 Default Access and Trunk Port Mode Parameters

Parameters

Default

Switchport mode

Access

Allowed VLANs

1 to 3967, 4048 to 4094

Access VLAN ID

VLAN1

Native VLAN ID

VLAN1

Native VLAN ID tagging

Disabled

Administrative state

Shut

Configuring Access and Trunk Interfaces


Note

If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.

Guidelines for Configuring Access and Trunk Interfaces

All VLANs on a trunk must be in the same VDC.

Configuring a VLAN Interface as a Layer 2 Access Port

You can configure a Layer 2 port as an access port. An access port transmits packets on only one, untagged VLAN. You specify which VLAN traffic that the interface carries, which becomes the access VLAN. If you do not specify a VLAN for an access port, that interface carries traffic only on the default VLAN. The default VLAN is VLAN1.

The VLAN must exist before you can specify that VLAN as an access VLAN. The system shuts down an access port that is assigned to an access VLAN that does not exist.

Before You Begin

Ensure that you are configuring a Layer 2 interface.

SUMMARY STEPS

    1.    configure terminal

    2.    interface ethernet {{type slot/port} | {port-channel number}}

    3.    switchport mode (access | trunk)

    4.    switchport access vlan vlan-id

    5.    exit

    6.    show interface

    7.    show interface status error policy [detail]

    8.    no shutdown

    9.    copy running-config startup-config


DETAILED STEPS
     Command or ActionPurpose
    Step 1configure terminal


    Example: 
    switch# configure terminal
switch(config)#
     

    Enters global configuration mode.

     
    Step 2interface ethernet {{type slot/port} | {port-channel number}}


    Example:
    switch(config)# interface ethernet 3/1
switch(config-if)#
     

    Specifies an interface to configure, and enters interface configuration mode.

     
    Step 3switchport mode (access | trunk)


    Example:
    switch(config-if)# switchport mode access
     

    Sets the interface as a nontrunking nontagged, single-VLAN Layer 2 interface. An access port can carry traffic in one VLAN only. By default, an access port carries traffic for VLAN1; to set the access port to carry traffic for a different VLAN, use the switchport access vlan command.

     
    Step 4switchport access vlan vlan-id


    Example:
    switch(config-if)# switchport access vlan 5
     

    Specifies the VLAN for which this access port will carry traffic. If you do not enter this command, the access port carries traffic on VLAN1 only; use this command to change the VLAN for which the access port carries traffic.

     
    Step 5exit


    Example:
    switch(config-if)# exit
switch(config)#
     

    Exits the interface configuration mode.

     
    Step 6show interface


    Example:
    switch# show interface
     

    (Optional) Displays the interface status and information.

     
    Step 7show interface status error policy [detail]


    Example:
    switch# show interface status error policy detail
     

    (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

    Use the detail command to display the details of the interfaces that produce an error.

     
    Step 8no shutdown


    Example:
    switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
     

    (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

     
    Step 9copy running-config startup-config


    Example:
    switch(config)# copy running-config startup-config
     

    (Optional) Copies the running configuration to the startup configuration.

     

    This example shows how to set Ethernet 3/1 as a Layer 2 access port that carries traffic for VLAN 5 only:

    switch# configure terminal 
switch(config)# interface ethernet 3/1
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 5
switch(config-if)#

    Configuring Access Host Ports


    Note

    You should apply the switchport host command only to interfaces that are connected to an end station.

    You can optimize the performance of access ports that are connected to end stations by simultaneously setting that port as an access port. An access host port handles the STP like an edge port and immediately moves to the forwarding state without passing through the blocking and learning states. Configuring an interface as an access host port also disables port channeling on that interface.


    Note

    See “Configuring Port Channels” section and the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for information about port-channel interfaces

    Before You Begin

    Ensure that you are configuring the correct interface to an interface that is an end station.

    SUMMARY STEPS

      1.    configure terminal

      2.    interface ethernet type slot/port

      3.    switchport host

      4.    exit

      5.    show interface

      6.    show interface status error policy [detail]

      7.    no shutdown

      8.    copy running-config startup-config


    DETAILED STEPS
       Command or ActionPurpose
      Step 1configure terminal


      Example: 
      switch# configure terminal
switch(config)#
       

      Enters global configuration mode.

       
      Step 2interface ethernet type slot/port


      Example:
      switch(config)# interface ethernet 3/1
switch(config-if)#
       

      Specifies an interface to configure, and enters interface configuration mode.

       
      Step 3switchport host


      Example:switch(config-if)# switchport host 

      Sets the interface to be an access host port, which immediately moves to the spanning tree forwarding state and disables port channeling on this interface.

      Note   

      Apply this command only to end stations.

       
      Step 4exit


      Example:
      switch(config-if-range)# exit
switch(config)#
       

      Exits the interface mode.

       
      Step 5show interface


      Example:
      switch# show interface
       

      (Optional) Displays the interface status and information.

       
      Step 6show interface status error policy [detail]


      Example:
      switch# show interface status error policy detail
       

      (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

      Use the detail command to display the details of the interfaces that produce an error.

       
      Step 7no shutdown


      Example:
      switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
       

      (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

       
      Step 8copy running-config startup-config


      Example:
      switch(config)# copy running-config startup-config
       

      (Optional) Copies the running configuration to the startup configuration.

       

      This example shows how to set Ethernet 3/1 as a Layer 2 access port with PortFast enabled and port channel disabled:

      switch# configure terminal 
switch(config)# interface ethernet 3/1
switch(config-if)# switchport host
switch(config-if)#

      Configuring Trunk Ports

      You can configure a Layer 2 port as a trunk port. A trunk port transmits untagged packets for one VLAN plus encapsulated, tagged, packets for multiple VLANs. (See the “IEEE 802.1Q Encapsulation” section for information about encapsulation.)


      Note

      The device supports 802.1Q encapsulation only.

      Before You Begin

      Before you configure a trunk port, ensure that you are configuring a Layer 2 interface.

      SUMMARY STEPS

        1.    configure terminal

        2.    interface {type slot/port | port-channel number}

        3.    switchport mode (access | trunk)

        4.    exit

        5.    show interface

        6.    show interface status error policy [detail]

        7.    no shutdown

        8.    copy running-config startup-config


      DETAILED STEPS
         Command or ActionPurpose
        Step 1configure terminal


        Example: 
        switch# configure terminal
switch(config)#
         

        Enters global configuration mode.

         
        Step 2interface {type slot/port | port-channel number}


        Example:
        switch(config)# interface ethernet 3/1
switch(config-if)#
         

        Specifies an interface to configure, and enters interface configuration mode.

         
        Step 3switchport mode (access | trunk)


        Example:
        switch(config-if)# switchport mode trunk
         

        Sets the interface as a Layer 2 trunk port. A trunk port can carry traffic in one or more VLANs on the same physical link (VLANs are based on the trunk-allowed VLANs list). By default, a trunk interface can carry traffic for all VLANs. To specify that only certain VLANs are allowed on the specified trunk, use the switchport trunk allowed vlan command.

         
        Step 4exit


        Example:
        switch(config-if)# exit
switch(config)#
         

        Exits the interface mode.

         
        Step 5show interface


        Example:
        switch# show interface
         

        (Optional) Displays the interface status and information.

         
        Step 6show interface status error policy [detail]


        Example:
        switch# show interface status error policy detail
         

        (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

        Use the detail command to display the details of the interfaces that produce an error.

         
        Step 7no shutdown


        Example:
        switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
         

        (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

         
        Step 8copy running-config startup-config


        Example:
        switch(config)# copy running-config startup-config
         

        (Optional) Copies the running configuration to the startup configuration.

         

        This example shows how to set Ethernet 3/1 as a Layer 2 trunk port:

        switch# configure terminal 
switch(config)# interface ethernet 3/1
switch(config-if)# switchport mode trunk
switch(config-if)#

        Configuring the Native VLAN for 802.1Q Trunking Ports

        You can configure the native VLAN for 802.1Q trunk ports. If you do not configure this parameter, the trunk port uses the default VLAN as the native VLAN ID.


        Note

        You cannot configure an FCoE VLAN as a native VLAN for an Ethernet interface.

        SUMMARY STEPS

          1.    configure terminal

          2.    interface {{type slot/port} | {port-channel number}}

          3.    switchport trunk native vlan vlan-id

          4.    exit

          5.    show vlan

          6.    show interface status error policy [detail]

          7.    no shutdown

          8.    copy running-config startup-config


        DETAILED STEPS
           Command or ActionPurpose
          Step 1configure terminal


          Example: 
          switch# configure terminal
switch(config)#
           

          Enters global configuration mode.

           
          Step 2interface {{type slot/port} | {port-channel number}}


          Example:
          switch(config)# interface ethernet 3/1
switch(config-if)#
           

          Specifies an interface to configure, and enters interface configuration mode.

           
          Step 3switchport trunk native vlan vlan-id


          Example:
          switch(config-if)# switchport trunk native vlan 5
           

          Sets the native VLAN for the 802.1Q trunk. Valid values are from 1 to 4094, except those VLANs reserved for internal use. The default value is VLAN1.

           
          Step 4exit


          Example:
          switch(config-if-range)# exit
switch(config)#
           

          Exits interface configuration mode.

           
          Step 5show vlan


          Example:
          switch# show vlan
           

          (Optional) Displays the status and information of VLANs.

           
          Step 6show interface status error policy [detail]


          Example:
          switch# show interface status error policy detail
           

          (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

          Use the detail command to display the details of the interfaces that produce an error.

           
          Step 7no shutdown


          Example:
          switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
           

          (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

           
          Step 8copy running-config startup-config


          Example:
          switch(config)# copy running-config startup-config
           

          (Optional) Copies the running configuration to the startup configuration.

           

          This example shows how to set the native VLAN for the Ethernet 3/1, Layer 2 trunk port to VLAN 5:

          switch# configure terminal 
switch(config)# interface ethernet 3/1
switch(config-if)# switchport trunk native vlan 5
switch(config-if)#

          Configuring the Allowed VLANs for Trunking Ports

          You can specify the IDs for the VLANs that are allowed on the specific trunk port.


          Note

          The switchport trunk allowed vlan vlan-list command replaces the current VLAN list on the specified port with the new list. You are prompted for confirmation before the new list is applied.

          If you are doing a copy and paste of a large configuration, you might see some failures because the CLI is waiting for a confirmation before accepting other commands. To avoid this problem, you can disable prompting by using the terminal dont-ask command before you paste the configuration.

          Before You Begin

          Before you configure the allowed VLANs for the specified trunk ports, ensure that you are configuring the correct interfaces and that the interfaces are trunks.


          Note

          You can change the block of VLANs reserved for internal use. See the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for more information about changing the reserved VLANs.

          SUMMARY STEPS

            1.    configure terminal

            2.    interface {ethernet slot/port | port-channel number}

            3.    switchport trunk allowed vlan {vlan-list add vlan-list | all | except vlan-list | none | remove vlan-list}

            4.    exit

            5.    show vlan

            6.    show interface status error policy [detail]

            7.    no shutdown

            8.    copy running-config startup-config


          DETAILED STEPS
             Command or ActionPurpose
            Step 1configure terminal


            Example: 
            switch# configure terminal
switch(config)#
             

            Enters global configuration mode.

             
            Step 2interface {ethernet slot/port | port-channel number}


            Example:
            switch(config)# interface ethernet 3/1
             

            Specifies an interface to configure, and enters interface configuration mode.

             
            Step 3switchport trunk allowed vlan {vlan-list add vlan-list | all | except vlan-list | none | remove vlan-list}


            Example:
            switch(config-if)# switchport trunk allowed vlan add 15-20#
             

            Sets the allowed VLANs for the trunk interface. The default is to allow all VLANs on the trunk interface: 1 to 3967 and 4048 to 4094. VLANs 3968 to 4047 are the default VLANs reserved for internal use by default. By default, all VLANs are allowed on all trunk interfaces.

            The default reserved VLANs are 3968 to 4094, and you can change the block of reserved VLANs. See the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for more information.

            Note   

            You cannot add internally allocated VLANs as allowed VLANs on trunk ports. The system returns a message if you attempt to list an internally allocated VLAN as an allowed VLAN.

             
            Step 4exit


            Example:
            switch(config-if)# exit
switch(config)#
             

            Exits the interface mode.

             
            Step 5show vlan


            Example:
            switch# show vlan
             

            (Optional) Displays the status and information for VLANs.

             
            Step 6show interface status error policy [detail]


            Example:
            switch# show interface status error policy detail
             

            (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

            Use the detail command to display the details of the interfaces that produce an error.

             
            Step 7no shutdown


            Example:
            switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
             

            (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

             
            Step 8copy running-config startup-config


            Example:
            switch(config)# copy running-config startup-config
             

            (Optional) Copies the running configuration to the startup configuration.

             

            This example shows how to add VLANs 15 to 20 to the list of allowed VLANs on the Ethernet 3/1, Layer 2 trunk port:

            switch# configure terminal 
switch(config)# interface ethernet 3/1
switch(config-if)# switchport trunk allowed vlan 15-20
switch(config-if)#

            Configuring a Default Interface

            The default interface feature allows you to clear the existing configuration of multiple interfaces such as Ethernet, loopback, VLAN network, port-channel, and tunnel interfaces. All user configuration under a specified interface will be deleted. You can optionally create a checkpoint before clearing the interface configuration so that you can later restore the deleted configuration.


            Note

            The default interface feature is not supported for management interfaces because the device could go to an unreachable state.

            SUMMARY STEPS

              1.    configure terminal

              2.    default interface int-if [checkpoint name]

              3.    exit

              4.    show interface

              5.    show interface status error policy [detail]

              6.    no shutdown


            DETAILED STEPS
               Command or ActionPurpose
              Step 1configure terminal


              Example: 
              switch# configure terminal
switch(config)#
               

              Enters global configuration mode.

               
              Step 2default interface int-if [checkpoint name]


              Example:
              switch(config)# default interface ethernet 3/1 checkpoint test8
               

              Deletes the configuration of the interface and restores the default configuration. Use the ? keyword to display the supported interfaces.

              Use the checkpoint keyword to store a copy of the running configuration of the interface before clearing the configuration.

               
              Step 3exit


              Example:
              switch(config)# exit
switch(config)#
               

              Exits global configuration mode.

               
              Step 4show interface


              Example:
              switch# show interface
               

              (Optional) Displays the interface status and information.

               
              Step 5show interface status error policy [detail]


              Example:
              switch# show interface status error policy detail
               

              (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

              Use the detail command to display the details of the interfaces that produce an error.

               
              Step 6no shutdown


              Example:
              switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
               

              (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

               

              This example shows how to delete the configuration of an Ethernet interface while saving a checkpoint of the running configuration for rollback purposes:

              switch# configure terminal 
switch(config)# default interface ethernet 3/1 checkpoint test8
.......Done 
switch(config)#

              Configuring SVI Autostate Exclude

              You can configure the SVI Autostate Exclude feature on an Ethernet interface or a port channel. You can use the Autostate Exclude option to enable or disable the port from bringing up or down the SVI calculation and applying it to all VLANs that are enabled on the selected port. (see Figure 3-5). You can also use the SVI Autostate Exlude VLAN feature to exclude a VLAN from the autostate excluded interface.

              SUMMARY STEPS

                1.    configure terminal

                2.    interface {{type slot/port} | {port-channel number}}

                3.    switchport

                4.    [no] switchport autostate exclude

                5.    [no] switchport autostate exclude vlan vlan id

                6.    exit

                7.    show running-config interface {{type slot/port} | {port-channel number}}

                8.    show interface status error policy [detail]

                9.    no shutdown

                10.    copy running-config startup-config


              DETAILED STEPS
                 Command or ActionPurpose
                Step 1configure terminal


                Example: 
                switch# configure terminal
switch(config)#
                 

                Enters global configuration mode.

                 
                Step 2interface {{type slot/port} | {port-channel number}}


                Example: 
                switch(config)# interface ethernet 3/1
switch(config-if)#
                 

                Specifies an interface to configure, and enters interface configuration mode.

                 
                Step 3switchport


                Example: 
                switch(config-if)# switchport
                 

                Sets the interface as a Layer 2 interface.

                 
                Step 4[no] switchport autostate exclude


                Example: 
                switch(config-if)# switchport autostate exclude
                 

                Excludes this port from the VLAN interface link-up calculation when there are multiple ports in the VLAN.

                To revert to the default settings, use the no form of this command.

                 
                Step 5[no] switchport autostate exclude vlan vlan id


                Example: 
                switch(config-if)# switchport autostate exclude vlan 10
                 

                (Optional) Excludes a vlan or a set of vlans from the autostate-excluded interface. This will help to minimize any disruption to the system.

                To revert to the default settings, use the no form of this command.

                 
                Step 6exit


                Example: 
                switch(config-if)# exit
switch(config)#
                 

                Exits the interface configuration mode.

                 
                Step 7show running-config interface {{type slot/port} | {port-channel number}}


                Example: 
                switch(config)# show running-config interface ethernet 3/1
                 

                (Optional) Displays configuration information about the specified interface.

                 
                Step 8show interface status error policy [detail]


                Example: 
                switch# show interface status error policy detail
                 

                (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

                Use the detail command to display the details of the interfaces that produce an error.

                 
                Step 9no shutdown


                Example: 
                switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
                 

                (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

                 
                Step 10copy running-config startup-config


                Example: 
                switch(config)# copy running-config startup-config
                 

                (Optional) Copies the running configuration to the startup configuration.

                 

                This example shows how to exclude a port from the VLAN interface link-up calculation on the Cisco NX-OS device: 

                switch# configure terminal 
switch(config)# interface ethernet 3/1
switch(config-if)# switchport
switch(config-if)# switchport autostate exclude

                This example shows how to exclude a VLAN from the auto-excluded interface: 

                switch# configure terminal 
switch(config)# interface ethernet 3/1
switch(config-if)# switchport
switch(config-if)# switchport autostate exclude
switch(config-if)# switchport autostate exclude vlan 10

                Configuring SVI Autostate Disable for the System

                You can configure the SVI autostate disable feature to keep an SVI up even if no interface is up in the corresponding VLAN. Use this procedure to configure this feature for the entire system.


                Note

                The system default interface vlan autostate command enables the SVI autostate feature.

                SUMMARY STEPS

                  1.    configure terminal

                  2.    system default interface-vlan no autostate

                  3.    show interface status error policy [detail]

                  4.    no shutdown

                  5.    show running-config [all]


                DETAILED STEPS
                   Command or ActionPurpose
                  Step 1configure terminal


                  Example: 
                  switch# configure terminal
switch(config)#
                   

                  Enters global configuration mode.

                   
                  Step 2system default interface-vlan no autostate


                  Example: 
                  switch(config)# system default interface-vlan no autostate
                   

                  Disables the default autostate behavior for the device.

                   
                  Step 3show interface status error policy [detail]


                  Example: 
                  switch# show interface status error policy detail
                   

                  (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

                  Use the detail command to display the details of the interfaces that produce an error.

                   
                  Step 4no shutdown


                  Example: 
                  switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
                   

                  (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

                   
                  Step 5show running-config [all]


                  Example: 
                  switch(config)# show running-config
                   

                  (Optional) Displays the running configuration.

                  To display the default and configured information, use the all keyword.

                   

                  This example shows how to disable the default autostate behavior on the Cisco NX-OS device: 

                  switch# configure terminal 
switch(config)# system default interface-vlan no autostate
switch(config)# show running-config

                  Configuring SVI Autostate Disable Per SVI

                  You can configure SVI autostate enable or disable on individual SVIs. The SVI-level setting overrides the system-level SVI autostate configuration for that particular SVI.

                  SUMMARY STEPS

                    1.    configure terminal

                    2.    feature interface-vlan

                    3.    interface vlan vlan-id

                    4.    [no] autostate

                    5.    exit

                    6.    show running-config interface vlan vlan-id

                    7.    show interface status error policy [detail]

                    8.    no shutdown

                    9.    show startup-config interface vlan vlan-id


                  DETAILED STEPS
                     Command or ActionPurpose
                    Step 1configure terminal


                    Example: 
                    switch# configure terminal
switch(config)#
                     

                    Enters global configuration mode.

                     
                    Step 2feature interface-vlan


                    Example: 
                    switch(config)# feature interface-vlan
                     

                    Enables VLAN interface mode.

                     
                    Step 3interface vlan vlan-id


                    Example: 
                    switch(config-if)# interface vlan10

switch(config)#
                     

                    Creates a VLAN interface and enters interface configuration mode. The range is from 1 and 4094.

                     
                    Step 4[no] autostate


                    Example: 
                    switch(config-if)# no autostate
                     

                    By default, enables the SVI autostate feature on specified interface.

                    To disable the default settings, use the no form of this command.

                     
                    Step 5exit


                    Example: 
                    switch(config-if)# exit
switch(config)#
                     

                    Exits the interface configuration mode.

                     
                    Step 6show running-config interface vlan vlan-id


                    Example: 
                    switch(config)# show running-config interface vlan10
                     

                    (Optional) Displays the running configuration for the specified VLAN interface.

                     
                    Step 7show interface status error policy [detail]


                    Example: 
                    switch# show interface status error policy detail
                     

                    (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

                    Use the detail command to display the details of the interfaces that produce an error.

                     
                    Step 8no shutdown


                    Example: 
                    switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
                     

                    (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

                     
                    Step 9show startup-config interface vlan vlan-id


                    Example: 
                    switch(config)# show startup-config interface vlan10
                     

                    (Optional) Displays the VLAN configuration in the startup configuration.

                     

                    This example shows how to disable the default autostate behavior on an individual SVI: 

                    switch# configure terminal 
switch(config)# feature interface-vlan
switch(config)# interface vlan10
witch(config-if)# no autostate

                    Configuring the Device to Tag Native VLAN Traffic

                    When you are working with 802.1Q trunked interfaces, you can maintain the tagging for all packets that enter with a tag that matches the value of the native VLAN ID and drops all untagged traffic (you will still carry control traffic on that interface). This feature applies to the entire device; you cannot apply it to selected VLANs on a device.

                    The vlan dot1q tag native global command changes the behavior of all native VLAN ID interfaces on all trunks on the device.


                    Note

                    If you enable 802.1Q tagging on one device and disable it on another device, all traffic is dropped on the device and this feature is disabled. You must configure this feature identically on each device.

                    SUMMARY STEPS

                      1.    configure terminal

                      2.    vlan dot1q tag native

                      3.    exit

                      4.    show vlan

                      5.    show interface status error policy [detail]

                      6.    no shutdown

                      7.    copy running-config startup-config


                    DETAILED STEPS
                       Command or ActionPurpose
                      Step 1configure terminal


                      Example: 
                      switch# configure terminal
switch(config)#
                       

                      Enters global configuration mode.

                       
                      Step 2vlan dot1q tag native


                      Example: 
                      switch(config)# vlan dot1q tag native
                       

                      Modifies the behavior of a 802.1Q trunked native VLAN ID interface. The interface maintains the taggings for all packets that enter with a tag that matches the value of the native VLAN ID and drops all untagged traffic. The control traffic is still carried on the native VLAN. The default is disabled.

                       
                      Step 3exit


                      Example: 
                      switch(config-if-range)# exit
switch(config)#
                       

                      Exits the interface configuration mode.

                       
                      Step 4show vlan


                      Example: 
                      switch# show vlan
                       

                      (Optional) Displays the status and information for VLANs.

                       
                      Step 5show interface status error policy [detail]


                      Example: 
                      switch# show interface status error policy detail
                       

                      (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

                      Use the detail command to display the details of the interfaces that produce an error.

                       
                      Step 6no shutdown


                      Example: 
                      switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
                       

                      (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

                       
                      Step 7copy running-config startup-config


                      Example: 
                      switch(config)# copy running-config startup-config
                       

                      (Optional) Copies the running configuration to the startup configuration.

                       

                      This example shows how to change the behavior of the native VLAN on an 802.1Q trunked interface to maintain the tagged packets and drop all untagged traffic (except control traffic): 

                      switch# configure terminal 
switch(config)# vlan dot1q tag native
switch#

                      Changing the System Default Port Mode to Layer 2

                      You can set the system default port mode to Layer 2 access ports.

                      SUMMARY STEPS

                        1.    configure terminal

                        2.    system default switchport [shutdown]

                        3.    exit

                        4.    show interface brief

                        5.    show interface status error policy [detail]

                        6.    no shutdown

                        7.    copy running-config startup-config


                      DETAILED STEPS
                         Command or ActionPurpose
                        Step 1configure terminal


                        Example: 
                        switch# configure terminal
switch(config)#
                         

                        Enters global configuration mode.

                         
                        Step 2system default switchport [shutdown]


                        Example:switch(config-if)# system default switchport  

                        Sets the default port mode for all interfaces on the system to Layer 2 access port mode and enters interface configuration mode. By default, all the interfaces are Layer 3.

                        Note   

                        When the system default switchport shutdown command is issued, any FEX HIFs that are not configured with no shutdown are shutdown. To avoid the shutdown, configure the FEX HIFs with no shut.

                         
                        Step 3exit


                        Example: 
                        switch(config-if)# exit
switch(config)#
                         

                        Exits the interface configuration mode.

                         
                        Step 4show interface brief


                        Example: 
                        switch# show interface brief
                         

                        (Optional) Displays the status and information for interfaces.

                         
                        Step 5show interface status error policy [detail]


                        Example: 
                        switch# show interface status error policy detail
                         

                        (Optional) Displays the interfaces and VLANs that produce errors during policy programming to ensure that policies are consistent with hardware policies.

                        Use the detail command to display the details of the interfaces that produce the errors.

                         
                        Step 6no shutdown


                        Example: 
                        switch# configure terminal
switch(config)# int e3/1
switch(config-if)# no shutdown
                         

                        (Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

                         
                        Step 7copy running-config startup-config


                        Example: 
                        switch(config)# copy running-config startup-config
                         

                        (Optional) Copies the running configuration to the startup configuration.

                         

                        This example shows how to set the system ports to be Layer 2 access ports by default: 

                        switch# configure terminal 
switch(config-if)# system default switchport
switch(config-if)#

                        Verifying the Interface Configuration

                        To display access and trunk interface configuration information, perform one of the following tasks.

                        Command

                        Purpose

                        show interface ethernet slot/port [brief | | counters | debounce | description | flowcontrol | mac-address | status | transceiver]

                        Displays the interface configuration.

                        show interface brief

                        Displays interface configuration information, including the mode.

                        show interface switchport

                        Displays information, including access and trunk interface, information for all Layer 2 interfaces.

                        show interface trunk [module module-number | vlan vlan-id]

                        Displays trunk configuration information.

                        show interface capabilities

                        Displays information about the capabilities of the interfaces.

                        show interface status error policy [detail]

                        Displays errors about interfaces and VLANs that are inconsistent with hardware policies.

                        The detail command displays the details of the interfaces that produce an error.

                        show running-config [all]

                        Displays information about the current configuration.

                        The all command displays the default and current configurations.

                        show running-config interface ethernet slot/port

                        Displays configuration information about the specified interface.

                        show running-config interface port-channel slot/port

                        Displays configuration information about the specified port-channel interface.

                        show running-config interface vlan vlan-id

                        Displays configuration information about the specified VLAN interface.

                        Monitoring the Layer 2 Interfaces

                        Use the following commands to display Layer 2 interfaces:

                        Command

                        Purpose

                        clear counters interface [interface]

                        Clears the counters.

                        load- interval {interval seconds {1 | 2 | 3}}

                        Cisco Nexus 9000 Series devices set three different sampling intervals to bit-rate and packet-rate statistics.

                        show interface counters [module module]

                        Displays input and output octets unicast packets, multicast packets, and broadcast packets.

                        show interface counters detailed [all]

                        Displays input packets, bytes, and multicast as well as output packets and bytes.

                        show interface counters errors [module module]

                        Displays information on the number of error packets.

                        Configuration Examples for Access and Trunk Ports

                        This example shows how to configure a Layer 2 access interface and assign the access VLAN mode for that interface:

                        switch# configure terminal
switch(config)# interface ethernet 2/30
switch(config-if)# switchport
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 5
switch(config-if)#

                        This example shows how to configure a Layer 2 trunk interface, assign the native VLAN and the allowed VLANs, and configure the device to tag the native VLAN traffic on the trunk interface:

                        switch# configure terminal
switch(config)# interface ethernet 2/35
switch(config-if)# switchport
switch(config-if)# switchport mode trunk
switch(config-if)# switchport trunk native vlan 10
switch(config-if)# switchport trunk allowed vlan 5, 10
switch(config-if)# exit
switch(config)# vlan dot1q tag native
switch(config)#

                        Related Documents

                        Related Documents

                        Document Title

                        Configuring Layer 3 interfaces

                        Configuring Layer 2 Interfaces section

                        Port Channels

                        Configuring Port Channels section

                        VLANs, private VLANs, and STP

                        Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide

                        System management

                        Cisco Nexus 9000 Series NX-OS System Management Configuration Guide

                        High availability

                        Cisco Nexus 9000 Series NX-OS High Availability and Redundancy Guide

                        VDCs

                        Cisco Nexus 9000 Series NX-OS Virtual Device Context Configuration Guide

                        Licensing

                        Cisco NX-OS Licensing Guide

                        Release Notes

                        Cisco Nexus 9000 Series NX-OS Release Notes