Configuring VLANs

This chapter contains the following sections:

Information About VLANs

Understanding VLANs

A VLAN is a group of end stations in a switched network that is logically segmented by function, project team, or application, without the limitation 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 port can belong to a VLAN; all unicast, broadcast, and multicast packets are forwarded and flooded only to end stations in that VLAN. Each VLAN is considered a logical network. If a packet destination address does not belong to the VLAN, it must be forwarded through a router.

The following figure shows VLANs as logical networks. In this diagram, 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 yet 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. To disable the VLAN use the shutdown command. Additionally, you can configure VLANs to be in the active state (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.


Note

The VLAN Trunking Protocol (VTP) mode is OFF. VTP BPDUs are dropped on all interfaces of the switch. This process has the effect of partitioning VTP domains if other switches have VTP turned on.

A VLAN can also be configured as a switched virtual interface (SVI). In this case, the switch ports in the VLAN are represented by a virtual interface to a routing or bridging system. The SVI can be configured for routing, in which case it supports Layer 3 protocols for processing packets from all switch ports associated with the VLAN, or for in-band management of the switch.

Understanding VLAN Ranges

The Cisco Nexus device supports VLAN numbers 1 to 4094 in accordance with the IEEE 802.1Q standard. These VLANs are organized into ranges. The switch is physically limited in the number of VLANs it can support. The hardware also shares this available range with its VSANs. For information about VLAN and VSAN configuration limits, see the configuration limits documentation for your device.

The following table describes the details of 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—4094

Extended

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

  • State is always active.

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

3968—4049 and 4094

Internally allocated

These 82 VLANs, plus VLAN 4094, are allocated for internal use. You cannot create, delete, or modify any VLANs within the block reserved for internal use.


Note

You cannot configure the internally allocated VLANs (reserved VLANs).


Note

VLANs 3968 to 4049 and 4094 are reserved for internal use; these VLANs cannot be changed or used.

Cisco NX-OS allocates a group of 82 VLAN numbers for those features, such as multicast and diagnostics, that need to use internal VLANs for their operation. By default, the system allocates VLANs numbered 3968 to 4049 for internal use. VLAN 4094 is also reserved for internal use by the switch.

You cannot use, modify, or delete any of the VLANs in the reserved group. You can display the VLANs that are allocated internally and their associated use.

Creating, Deleting, and Modifying VLANs

VLANs are numbered from 1 to 4094. All configured ports belong to the default VLAN when you first bring up the switch. The default VLAN (VLAN1) uses only default values. 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 as well as 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 switch goes into the VLAN submode but does not create the same VLAN again.

Newly created VLANs remain unused until 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

  • Shutdown or not shutdown

When you delete a specified VLAN, the ports associated to that VLAN are shut down and no traffic flows. However, the system retains all the VLAN-to-port mapping for that VLAN, and when you reenable, or recreate, the specified VLAN, the system automatically reinstates all the original ports to that VLAN.


Note

Commands entered in the VLAN configuration submode are immediately executed.

VLANs 3968 to 4049 and 4094 are reserved for internal use; these VLANs cannot be changed or used.

About the VLAN Trunking Protocol

VLAN Trunking Protocol (VTP) is a distributed VLAN database management protocol that synchronizes the VTP VLAN database across domains. A VTP domain includes one or more network switches that share the same VTP domain name and are connected with trunk interfaces.

The following are the different VTP modes:

  • Server mode—Allows users to perform configurations, manage the VLAN database version, and store the VLAN database.

  • Client mode—Does not allow users to perform configurations and relies on other switches in the domain to provide configuration information.

  • Off mode—Allows users to access the VLAN database (VTP is enabled) but does not participate in VTP.

  • Transparent mode—Does not participate in VTP, uses local configuration, and relays VTP packets to other forward ports. VLAN changes affect only the local switch. A VTP transparent network switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements.

Guidelines and Limitations for VTP

VTP has the following configuration guidelines and limitations:

  • When a switch is configured as a VTP client, you cannot create VLANs on the switch in the range of 1 to 1005.

  • VLAN 1 is required on all trunk ports used for switch interconnects if VTP is supported in the network. Disabling VLAN 1 from any of these ports prevents VTP from functioning properly.

  • If you enable VTP, you must configure either version 1 or version 2. On the Cisco Nexus device, 512 VLANs are supported. If these switches are in a distribution network with other switches, the limit remains the same.

    On the Cisco Nexus device, 512 VLANs are supported. If these switches are in a distribution network with other switches, the VLAN limit for the VTP domain is 512. If a Cisco Nexus device client/server receives additional VLANs from a VTP server, they transition to transparent mode.

  • If system vlan long-name knob is enabled, then VTP configurations will come up in OFF mode and users can change the mode to Transparent. However, changing the mode to Server or Client is not allowed.

  • The show running-configuration command does not show VLAN or VTP configuration information for VLANs 1 to 1000.

  • When deployed with vPC, both vPC switches must be configured identically.

  • VTP advertisements are not sent out on Cisco Nexus Fabric Extender ports.

  • Private VLANs (PVLANs) are supported only when the switch is in transparent mode.

  • When a switch is configured in VTP client or server mode, VLANs 1002 to1005 are reserved VLANs.

  • VTP pruning is not supported.

  • You must enter the copy running-config startup-config command followed by a reload after changing a reserved VLAN range. For example: 

    switch(config)# system vlan 2000 reserve 
This will delete all configs on vlans 2000-2081. Continue anyway? (y/n) [no] y

    After the switch reload, VLANs 2000 to 2081 are reserved for internal use, which requires that you enter the copy running-config startup-config command before the switch reload. Creating VLANs within this range is not allowed.

Configuring a VLAN

Creating and Deleting a VLAN

You can create or delete all VLANs except the default VLAN and those VLANs that are internally allocated for use by the switch. Once a VLAN is created, it is automatically in the active state.


Note

When you delete a VLAN, ports associated to that VLAN shut down. The traffic does not flow and the packets are dropped.

SUMMARY STEPS

    1.    switch# configure terminal

    2.    switch(config)# vlan {vlan-id | vlan-range}

    3.    switch(config-vlan)# no vlan {vlan-id | vlan-range}


DETAILED STEPS
     Command or ActionPurpose
    Step 1switch# configure terminal  

    Enters global configuration mode.

     
    Step 2 switch(config)# vlan {vlan-id | vlan-range}
     

    Creates a VLAN or a range of VLANs.

    If you enter a number that is already assigned to a VLAN, the switch moves 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 4094; 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 switch(config-vlan)# no vlan {vlan-id | vlan-range}
     

    Deletes the specified VLAN or range of VLANs and removes you from the VLAN configuration submode. You cannot delete VLAN1 or the internally allocated VLANs.

     

    This example shows how to create a range of VLANs from 15 to 20: 

    switch# configure terminal
switch(config)# vlan 15-20

    Note

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

    Changing the Range of Reserved VLANs

    To change the range of reserved VLANs, you must be in global configuration mode. After entering this command, you must do the following tasks:

    • Enter the copy running-config startup-config command

    • Reload the device

    SUMMARY STEPS

      1.    config t

      2.    system vlan start-vlan reserve

      3.    copy running-config startup-config

      4.    reload

      5.    (Optional) show system vlan reserved


    DETAILED STEPS
       Command or ActionPurpose
      Step 1config t


      Example: 
      switch# config t
switch(config)#
       

      Enters global configuration mode.

       
      Step 2 system vlan start-vlan reserve


      Example: 
      switch(config)# system vlan 3968 reserve
       

      Allows you to change the reserved VLAN range by specifying the starting VLAN ID for your desired range.

      You can change the reserved VLANs to any other 82 contiguous VLAN ranges. When you reserve such a range, it frees up the range of VLANs that were allocated for internal use by default, and all of those VLANs are available for user configuration except for VLAN 4094.

      Note   

      To return to the default range of reserved VLANs (3968-4049 and 4094), you must enter the no system vlan start-vlan reserve command.

       
      Step 3 copy running-config startup-config


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

      Copies the running configuration to the startup configuration.

      Note   

      You must enter this command if you change the reserved block.

       
      Step 4 reload


      Example: 
      switch(config)# reload
       

      Reloads the software, and modifications to VLAN ranges become effective.

      For more details about this command, see the Cisco Nexus 7000 Series NX-OS Fundamentals Configuration Guide, Release 6.x.

       
      Step 5 show system vlan reserved


      Example: 
      switch(config)# show system vlan reserved
              		(Optional)

      Displays the configured changes to the VLAN range.

       
      This example shows how to change the range of reserved VLANs: 
      switch# configuration terminal
switch(config)# system vlan 1006 reserve
This will delete all configs on vlans 1006-1087. Continue anyway? (y/n) [no] yes 
Note: After switch reload, VLANs 1006-1087 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)# copy running-config startup-config
switch(config)# reload
switch(config)# show system vlan reserved

      Note

      You must reload the device for this change to take effect.

      Configuring a VLAN

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

      • Name


        Note
        VLAN name can be either a short name (up to 32 characters) or long name (up to 128 characters). To configure VLAN long-name of up to 128 characters, you must enable system vlan long-name command.

      • 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.    switch# configure terminal

        2.    switch(config)# vlan {vlan-id | vlan-range}

        3.    switch(config-vlan)# name vlan-name

        4.    switch(config-vlan)# state {active | suspend}

        5.    (Optional) switch(config-vlan)# no shutdown


      DETAILED STEPS
         Command or ActionPurpose
        Step 1switch# configure terminal  

        Enters global configuration mode.

         
        Step 2 switch(config)# vlan {vlan-id | vlan-range}
         

        Enters VLAN configuration submode. If the VLAN does not exist, the system first creates the specified VLAN.

         
        Step 3 switch(config-vlan)# name vlan-name
         

        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 represents four numeric digits (including leading zeroes) equal to the VLAN ID number.

         
        Step 4 switch(config-vlan)# state {active | suspend}
         

        Sets the state of the VLAN to active or suspend. While the VLAN state is suspended, the ports associated with this VLAN are shut down, 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 4094.

         
        Step 5 switch(config-vlan)# no shutdown
                  		(Optional)

        Enables the VLAN. The default value is no shutdown (or enabled). You cannot shut down the default VLAN, VLAN1, or VLANs 1006 to 4094.

         

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

        switch# configure terminal
        switch(config)# vlan 5
        switch(config-vlan)# name accounting
        switch(config-vlan)# state active
        switch(config-vlan)# no shutdown

        Adding Ports to a VLAN

        After you have completed the configuration of a VLAN, assign ports to it.

        SUMMARY STEPS

          1.    switch# configure terminal

          2.    switch(config)# interface {ethernet slot/port | port-channel number}

          3.    switch(config-if)# switchport access vlan vlan-id


        DETAILED STEPS
           Command or ActionPurpose
          Step 1switch# configure terminal  

          Enters global configuration mode.

           
          Step 2 switch(config)# interface {ethernet slot/port | port-channel number}
           

          Specifies the interface to configure, and enters the interface configuration mode. The interface can be a physical Ethernet port or an EtherChannel.

           
          Step 3 switch(config-if)# switchport access vlan vlan-id
           

          Sets the access mode of the interface to the specified VLAN.

           

          This example shows how to configure an Ethernet interface to join VLAN 5:

          switch# configure terminal

          switch(config)# interface ethernet 1/13

          switch(config-if)# switchport access vlan 5

          Verifying the VLAN Configuration

          Use one of the following commands to verify the configuration:

          Command

          Purpose
          switch# show running-config vlan [vlan_id | vlan_range]

          Displays VLAN information.
          switch# show vlan [brief | id [vlan_id | vlan_range] | name name | summary ]

          Displays selected configuration information for the defined VLAN(s).
          switch# show system vlan reserved

          Displays the system reserved VLAN range.