Configuring VLANs

Information About VLANs

You can use VLANs to divide the network into separate logical areas at the Layer 2 level. VLANs can also be considered as broadcast domains.

Any switch port can belong to a VLAN, and unicast broadcast and multicast packets are forwarded and flooded only to end stations in that VLAN. Each VLAN is considered a logical network, and packets destined for stations that do not belong to the VLAN must be forwarded through a router.

Understanding VLANs

A VLAN is a group of end stations in a switched network that is logically segmented by function or application, without regard to the physical locations of the users. VLANs have the same attributes as physical LANs, but you can group end stations even if they are not physically located on the same LAN segment.

Any switch port can belong to a VLAN, and unicast, broadcast, and multicast packets are forwarded and flooded only to end stations in that VLAN. Each VLAN is considered as a logical network, and packets destined for stations that do not belong to the VLAN must be forwarded through a router. The following figure shows VLANs as logical networks. The stations in the engineering department are assigned to one VLAN, the stations in the marketing department are assigned to another VLAN, and the stations in the accounting department are assigned to another VLAN.

Figure 1. VLANs as Logically Defined Networks



VLANs are usually associated with IP subnetworks. For example, all the end stations in a particular IP subnet belong to the same VLAN. To communicate between VLANs, you must route the traffic.

By default, a newly created VLAN is operational; that is, the newly created VLAN is in the no shutdown condition. Additionally, you can configure VLANs to be in the active state, which is passing traffic, or the suspended state, in which the VLANs are not passing packets. By default, the VLANs are in the active state and pass traffic.

A VLAN interface, or switched virtual interface (SVI), is a Layer 3 interface that is created to provide communication between VLANs. In order to route traffic between VLANs, you must create and configure a VLAN interface for each VLAN. Each VLAN requires only one VLAN interface.

VLAN Ranges


Note

The extended system ID is always automatically enabled in Cisco Nexus 9000 devices.

The device supports up to 4095 VLANs in accordance with the IEEE 802.1Q standard. The software organizes these VLANs into ranges, and you use each range slightly differently.

For information about configuration limits, see the verified scalability limits documentation for your switch.

This table describes the VLAN ranges.

Table 1 VLAN Ranges

VLANs Numbers

Range

Usage

1

Normal

Cisco default. You can use this VLAN, but you cannot modify or delete it.

2—1005

Normal

You can create, use, modify, and delete these VLANs.

1006—3967

Extended

You can create, name, and use these VLANs. You cannot change the following parameters:

  • The state is always active.

  • The VLAN is always enabled. You cannot shut down these VLANs.

3968-4095

Internally allocated

These reserved VLANs are allocated for internal device use.

About Reserved VLANS

The following are notes about reserved VLANs (3968 to 4095):

  • The software allocates a group of VLAN numbers for features like multicast and diagnostics, that need to use internal VLANs for their operation. By default, the system allocates a block of 128 reserved VLANs (3968 to 4095) for these internal uses.

  • You can change the range of reserved VLANs with the system vlan vlan-id reserve command. This allows you to set a different range of VLANs to be used as the reserved VLANs. The selected VLANs must be reserved in groups of 128.

    • You may configure VLANs 3968-4092 for other purposes.

    • VLANs 4093-4095 are always reserved for internal use and cannot be used other purposes.

    For example, 
    system vlan 400 reserve
    reserves VLANs 400-527.

    The new reserved range takes effect after the running configuration is saved and the device is reloaded.

    • VLANs 4093-4095 are always reserved for internal use and cannot be used other purposes.

      In the example, the result of the command would be that VLANs 400-527 are reserved and that VLANs 4093-4095 are also reserved.

  • The no system vlan vlan-id reserve command changes the range for reserved VLANs to the default range of 3968-4095 after the device is reloaded.

  • Use the show system vlan reserved command to verify the range of the current and future reserved VLAN ranges.

  • Use the show vlan internal usage command to verify the use of different reserved VLANs.

Example of VLAN Reserve

The following is an example of configuring the VLAN reserve (before and after image reload): 

**************************************************
CONFIGURE NON-DEFAULT RANGE, "COPY R S" AND RELOAD
**************************************************
switch(config)# system vlan 400 reserve
"vlan configuration 400-527" will be deleted automatically. 
Vlans, SVIs and sub-interface encaps for vlans 400-527 need to be removed by the user. 
Continue anyway? (y/n) [no] y
Note: After switch reload, VLANs 400-527 will be reserved for internal use.
      This requires copy running-config to startup-config before
      switch reload.  Creating VLANs within this range is not allowed.

switch(config)# show system vlan reserved

system current running vlan reservation: 3968-4095

system future running vlan reservation: 400-527

switch(config)# show vlan internal usage

VLANs                   DESCRIPTION
-------------------     -----------------
3968-4031               Multicast
4032-4035,4048-4059     Online Diagnostic
4036-4039,4060-4087     ERSPAN
4042                    Satellite
3968-4095               Current
4041                    VXLAN Encap

switch(config)# copy running-config startup-config
[########################################] 100%

switch(config)# reload
This command will reboot the system. (y/n)?  [n] y

************
AFTER RELOAD
************

switch# show system vlan reserved

system current running vlan reservation: 400-527

switch# show vlan internal usage

VLANs                   DESCRIPTION
-------------------     -----------------
448-511                 Multicast
400-415                 Online Diagnostic
416-447                 ERSPAN
512                     Satellite
400-527,4093-4094       Current
514                     VXLAN Encap

Creating, Deleting, and Modifying VLANs


Note

By default, all Cisco Nexus 9396 and Cisco Nexus 93128 ports are Layer 2 ports.

By default, all Cisco Nexus 9504 and Cisco Nexus 9508 ports are Layer 3 ports.

VLANs are numbered from 1 to 3967. All ports that you have configured as switch ports belong to the default VLAN when you first bring up the switch as a Layer 2 device. The default VLAN (VLAN1) uses only default values, and you cannot create, delete, or suspend activity in the default VLAN.

You create a VLAN by assigning a number to it; you can delete VLANs and move them from the active operational state to the suspended operational state. If you attempt to create a VLAN with an existing VLAN ID, the device goes into the VLAN submode but does not create the same VLAN again.

Newly created VLANs remain unused until Layer 2 ports are assigned to the specific VLAN. All the ports are assigned to VLAN1 by default.

Depending on the range of the VLAN, you can configure the following parameters for VLANs (except the default VLAN):

  • VLAN name

  • VLAN state

  • Shutdown or not shutdown

You can configure VLAN long-names of up to 128 characters. To configure VLAN long-names, VTP must be in transparent mode.


Note

See the Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide for information on configuring ports as VLAN access or trunk ports and assigning ports to VLANs.

When you delete a specified VLAN, the ports associated to that VLAN become inactive and no traffic flows. When you delete a specified VLAN from a trunk port, only that VLAN is shut down and traffic continues to flow on all the other VLANs through the trunk port.

However, the system retains all the VLAN-to-port mapping for that VLAN, and when you reenable or re-create, that specified VLAN, the system automatically reinstates all the original ports to that VLAN. The static MAC addresses and aging time for that VLAN are not restored when the VLAN is reenabled.


Note

Commands entered in the VLAN configuration submode are not immediately executed. You must exit the VLAN configuration submode for configuration changes to take effect.

High Availability for VLANs

The software supports high availability for both stateful and stateless restarts, as during a cold reboot, for VLANs. For the stateful restarts, the software supports a maximum of three retries. If you try more than 3 times within 10 seconds of a restart, the software reloads the supervisor module.

You can upgrade or downgrade the software seamlessly when you use VLANs.


Note

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

Licensing Requirements for VLANs

The following table shows the licensing requirements for this feature.

Product

License Requirement

Cisco NX-OS

VLANs 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 Configuring VLANs

VLANs have the following prerequisites:

  • You must be logged onto the device.

  • You must create the VLAN before you can do any modification of that VLAN.

Guidelines and Limitations for Configuring VLANs

VLANs have the following configuration guidelines and limitations:

  • You can configure a single VLAN or a range of VLANs.

    When you configure a large number of VLANs, first create the VLANs using the vlan command (for example, vlan 200-300, 303-500). After the VLANS have been successfully created, name or configure those VLANs sequentially.

  • You cannot create, modify, or delete any VLANs that are within the group of VLANs reserved for internal use.

  • VLAN1 is the default VLAN. You cannot create, modify, or delete this VLAN.

  • VLANs 1006 to 3967 are always in the active state and are always enabled. You cannot suspend the state or shut down these VLANs.

  • When the spanning tree mode is changed, the Layer 3 subinterface VLANs that share the same VLAN IDs with Layer 2 VLANs might be affected by a few micro-seconds of traffic drops as a result of the hardware re-programming.

  • VLANs 3968 to 4095 are reserved for internal device use by default.

Default Settings for VLANs

This table lists the default settings for VLAN parameters.

Table 2 Default VLAN Parameters

Parameters

Default

VLANs

Enabled

VLAN

VLAN1—A port is placed in VLAN1 when you configure it as a switch port.

VLAN ID

1

VLAN name

  • Default VLAN (VLAN1)—default

  • All other VLANs—VLAN vlan-id

VLAN state

Active

STP

Enabled; Rapid PVST+ is enabled

VTP

Disabled

VTP version

1

Configuring a VLAN


Note

See the Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide, for information on assigning Layer 2 interfaces to VLANs (access or trunk ports). All interfaces are in VLAN1 by default.


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.

Creating and Deleting a VLAN - CLI Version

You can create or delete all VLANs except the default VLAN and those VLANs that are internally allocated for use by the device.

Once a VLAN is created, it is automatically in the active state.


Note

When you delete a VLAN, ports associated to that VLAN become inactive. Therefore, no traffic flows and the packets are dropped. On trunk ports, the port remains open and the traffic from all other VLANs except the deleted VLAN continues to flow.

If you create a range of VLANs and some of these VLANs cannot be created, the software returns a message listing the failed VLANs, and all the other VLANs in the specified range are created.


Note

You can also create and delete VLANs in the VLAN configuration submode.

SUMMARY STEPS

    1.    config t

    2.    vlan {vlan-id | vlan-range}

    3.    exit

    4.    (Optional) show vlan

    5.    (Optional) copy running-config startup-config


DETAILED STEPS
     Command or ActionPurpose
    Step 1 config t


    Example: 
    switch# config t
switch(config)#
     

    Enters configuration mode.

     
    Step 2 vlan {vlan-id | vlan-range}


    Example: 
    switch(config)# vlan 5
switch(config-vlan)#
     

    Creates a VLAN or a range or VLANs. If you enter a number that is already assigned to a VLAN, the device puts you into the VLAN configuration submode for that VLAN. If you enter a number that is assigned to an internally allocated VLAN, the system returns an error message. However, if you enter a range of VLANs and one or more of the specified VLANs is outside the range of internally allocated VLANs, the command takes effect on only those VLANs outside the range. The range is from 2 to 3967; VLAN1 is the default VLAN and cannot be created or deleted. You cannot create or delete those VLANs that are reserved for internal use.

     
    Step 3 exit


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

    Exits the VLAN mode.

     
    Step 4 show vlan


    Example: 
    switch# show vlan
          		(Optional)

    Displays information and status of VLANs.

     
    Step 5 copy 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 create a range of VLANs from 15 to 20:

    switch# config t 
switch(config)# vlan 15-20
switch(config-vlan)# exit
switch(config)#

    Entering the VLAN Configuration Submode

    To configure or modify the VLAN for the following parameters, you must be in the VLAN configuration submode:

    • Name

    • State

    • Shut down

    SUMMARY STEPS

      1.    config t

      2.    vlan {vlan-id | vlan-range}

      3.    exit

      4.    (Optional) show vlan

      5.    (Optional) copy running-config startup-config


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 config t


      Example: 
      switch# config t
switch(config)#
       

      Enters configuration mode.

       
      Step 2 vlan {vlan-id | vlan-range}


      Example: 
      switch(config)# vlan 5
switch(config-vlan)#
       

      Places you into the VLAN configuration submode. This submode allows you to name, set the state, disable, and shut down the VLAN or range of VLANs.

      You cannot change any of these values for VLAN1 or the internally allocated VLANs.

       
      Step 3 exit


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

      Exits the VLAN configuration mode.

       
      Step 4 show vlan


      Example: 
      switch# show vlan
              		(Optional)

      Displays information and status of VLANs.

       
      Step 5 copy 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 enter and exit the VLAN configuration submode: 

      switch# config t
switch(config)# vlan 15
switch(config-vlan)# exit
switch(config)#

      Configuring a VLAN

      To configure or modify a VLAN for the following parameters, you must be in the VLAN configuration submode:

      • Name

      • State

      • Shut down


      Note

      You cannot create, delete, or modify the default VLAN or the internally allocated VLANs. Additionally, some of these parameters cannot be modified on some VLANs.

      SUMMARY STEPS

        1.    config t

        2.    vlan {vlan-id | vlan-range}

        3.    name vlan-name

        4.    state {active | suspend}

        5.    no shutdown

        6.    exit

        7.    (Optional) show vlan

        8.    (Optional) show vtp status

        9.    (Optional) copy running-config startup-config


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 config t


        Example: 
        switch# config t
switch(config)#
         

        Enters configuration mode.

         
        Step 2 vlan {vlan-id | vlan-range}


        Example: 
        switch(config)# vlan 5
switch(config-vlan)#
         

        Places you into the VLAN configuration submode. If the VLAN does not exist, the system creates the specified VLAN and then enters the VLAN configuration submode.

         
        Step 3 name vlan-name


        Example: 
        switch(config-vlan)# name accounting
         

        Names the VLAN. You can enter up to 32 alphanumeric characters to name the VLAN. You cannot change the name of VLAN1 or the internally allocated VLANs. The default value is VLANxxxx where xxxx represent four numeric digits (including leading zeroes) equal to the VLAN ID number.

        Note   

        128-character names are supported (VLAN Long-Name).

         
        Step 4 state {active | suspend}


        Example: 
        switch(config-vlan)# state active
         

        Sets the state of the VLAN to active or suspend. While the VLAN state is suspended, the ports associated with this VLAN become inactive, and that VLAN does not pass any traffic. The default state is active. You cannot suspend the state for the default VLAN or VLANs 1006 to 3967.

         
        Step 5 no shutdown


        Example: 
        switch(config-vlan)# no shutdown
         

        Enables the VLAN. The default value is no shutdown (or enabled). You cannot shut down the default VLAN, VLAN1, or VLANs 1006 to 3967.

         
        Step 6 exit


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

        Exits the VLAN configuration submode.

         
        Step 7 show vlan


        Example: 
        switch# show vlan
                  		(Optional)

        Displays information and status of VLANs.

         
        Step 8show vtp status


        Example: 
        switch# show vtp status
                  		(Optional)

        Displays information and status of VLAN Trunking Protocols (VTPs).

         
        Step 9 copy running-config startup-config


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

        Copies the running configuration to the startup configuration.

        Note   

        Commands entered in the VLAN configuration submode are not immediately executed. You must exit the VLAN configuration submode for configuration changes to take effect.

         

        This example shows how to configure optional parameters for VLAN 5: 

        switch# config t
switch(config)# vlan 5 
switch(config-vlan)# name accounting 
switch(config-vlan)# state active 
switch(config-vlan)# no shutdown 
switch(config-vlan)# exit 
switch(config)#

        Configuring a VLAN Before Creating the VLAN

        You can configure a VLAN before you create the VLAN. This procedure is used for IGMP snooping, VTP, and other configurations.

        Note

        The show vlan command does not display these VLANs unless you create it using the vlan command.

        SUMMARY STEPS

          1.    config t

          2.    vlan configuration {vlan-id}


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 config t


          Example: 
          switch# config t
switch(config)#
           

          Enters configuration mode.

           
          Step 2 vlan configuration {vlan-id}


          Example: 
          switch(config)# vlan configuration 20
switch(config-vlan-config)#
           

          Allows you to configure VLANs without actually creating them.

           
          This example shows how to configure a VLAN before creating it: 
          switch# config t
switch(config)# vlan configuration 20
switch(config-vlan-config)#

          Enabling the VLAN Long-Name

          You can configure VLAN long-names of up to 128 characters.


          Note

          When system vlan long-name is included in the start-up configuration, the Cisco Nexus 9000 Series switch boots up in VTP off mode.

          To enable VTP transparent mode:

          1. Disable VTP

          2. Remove system vlan long-name from the start-up configuration

          3. Re-enable VTP

          Before You Begin

          VTP must be in transparent or in off mode. VTP cannot be in client or server mode. For more details about VTP, see Configuring VTP.

          SUMMARY STEPS

            1.    configure terminal

            2.    system vlan long-name

            3.    (Optional) copy running-config startup-config

            4.    show running-config vlan


          DETAILED STEPS
             Command or ActionPurpose
            Step 1configure terminal


            Example: 
            switch# configure terminal
switch(config)#
             

            Enters global configuration mode.

             
            Step 2system vlan long-name


            Example: 
            switch(config)# system vlan long-name
             

            Allows you to enable VLAN names that have up to 128 characters.

            Use the no form of this command to disable this feature.

             
            Step 3copy running-config startup-config


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

            Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

             
            Step 4show running-config vlan


            Example: 
            switch(config)# show running-config vlan
                          		Verifies that the system VLAN long-name feature is enabled.  
            This example shows how to enable VLAN long-names. 
            switch# configure terminal
switch(config)# system vlan long-name
switch(config)# copy running config startup config
switch(config)# show running-config vlan

            Verifying the VLAN Configuration

            To display VLAN configuration information, perform one of the following tasks:

            Command

            Purpose

            show running-config vlan vlan-id

            Displays VLAN information.

            show vlan [all-ports | brief | id vlan-id | name name | dot1q tag native]

            Displays VLAN information.

            show vlan summary

            Displays a summary of VLAN information.

            show vtp status

            Displays VTP information.

            Displaying and Clearing VLAN Statistics

            To display VLAN configuration information, perform one of the following tasks:

            Command

            Purpose

            clear vlan [id vlan-id] counters

            Clears counters for all VLANs or for a specified VLAN.

            show vlan counters

            Displays information on Layer 2 packets in each VLAN.

            Configuration Example for VLANs

            The following example shows how to create and name a VLAN as well as how to make the state active and administratively up:

            switch# configure terminal
switch(config)# vlan 10
switch(config-vlan)# name test
switch(config-vlan)# state active
switch(config-vlan)# no shutdown
switch(config-vlan)# exit
switch(config)#

            Additional References for VLANs

            Related Documents

            Related Topic

            Document Title

            NX-OS Layer 2 switching configuration

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

            Interfaces, VLAN interfaces, IP addressing, and port channels

            Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide

            Multicast routing

            Cisco Nexus 9000 Series NX-OS Multicast Routing Configuration Guide

            NX-OS fundamentals

            Cisco Nexus 9000 Series NX-OS Fundamentals Configuration Guide

            High availability

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

            System management

            Cisco Nexus 9000 Series NX-OS System Management Configuration Guide

            Standards

            Standards

            Title

            No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

            		—

            MIBs

            MIBs

            MIBs Link

            CISCO-VLAN-MEMBERSHIP MIB:

            • vmMembership Table

            • MIBvmMembershipSummaryTable

            • MIBvmMembershipSummaryTable

            To locate and download MIBs, go to the following URL: ftp:/​/​ftp.cisco.com/​pub/​mibs/​supportlists/​nexus9000/​Nexus9000MIBSupportList.html