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 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.

VLAN Ranges


Note

The extended system ID is always automatically enabled in Cisco NX-OS devices.

The device supports up to 4094 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 configuration 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 and 4048—4093

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.

3968-4047 and 4094

Internally allocated

These 80 VLANs and VLAN 4094 are allocated for internal device use. You cannot create, delete, or modify any VLANs within the block reserved for internal use.

The software allocates a group of VLAN numbers for features like multicast and diagnostics, that need to use internal VLANs for their operation. 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 4047 and 4094 are reserved for internal use; these VLANs cannot be changed or used.

About the 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 that are connected with trunk interfaces. Each device can be in one VTP domain, Layer 2 trunk interfaces, and Layer 2 port channels.

Guidelines and Limitations for VTP

VTP has the following configuration guidelines and limitations:

  • 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.

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

  • VTP pruning is not supported.

  • If you are using VTP in a Token Ring environment, you must use version 2.

  • 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 2000-2127. Continue anyway? (y/n) [no] y

    After the switch reload, VLANs 2000 to 2127 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.

  • SNMP can perform GET and SET operations on the CISCO-VTP-MIB objects.

  • VTP server mode and VTP client mode are not supported. The only supported mode is transparent mode, which is the default mode.

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.

Procedure
     Command or ActionPurpose
    Step 1 switch# configure terminal
     

    Enters 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 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 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 also create and delete VLANs in the VLAN configuration submode.

    Configuring a VLAN

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

    • Name

    • 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.

    Procedure
       Command or ActionPurpose
      Step 1 switch# configure terminal
       

      Enters 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 represent 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. To add ports, perform this task:

      Procedure
         Command or ActionPurpose
        Step 1 switch# configure terminal
         

        Enters 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

        Configuring a VLAN as a Routed SVI

        You can configure a VLAN to be a routed switch virtual interface (SVI).

        Before You Begin
        Procedure
           Command or ActionPurpose
          Step 1configure terminal
           

          Enters global configuration mode.

           
          Step 2feature interface-vlan
           

          Enables the creation of SVIs.

           
          Step 3 interface-vlan vlan-id
           

          Creates a VLAN interface (SVI) and enters interface configuration mode.

           
          Step 4 copy running-config startup-config
           

          Copies the running configuration to the startup configuration.

           
          The following example shows how to configure a VLAN as a routed SVI:
          switch# configure terminal
switch(config)# feature interface-vlan
switch(config)# interface vlan 5
switch(config-if)# copy running-config startup-config
switch(config-if)#

          The following example shows how to remove the routed SVI function from a VLAN:

          switch# configure terminal
switch(config)# no interface vlan 5
switch(config-if)# copy running-config startup-config
switch(config-if)#
          What to Do Next

          You can configure routing protocols on this interface.

          Configuring a VLAN as a Management SVI

          You can configure a VLAN to be a management switch virtual interface (SVI).

          Procedure
             Command or ActionPurpose
            Step 1configure terminal
             

            Enters global configuration mode.

             
            Step 2feature interface-vlan
             

            Enables the creation of SVIs.

             
            Step 3 interface-vlan vlan-id management
             

            Creates a VLAN interface (SVI) and configures the SVI to be used for in-band management.

             
            Step 4 copy running-config startup-config
             

            Copies the running configuration to the startup configuration.

             
            The following example shows how to configure a VLAN as a management SVI:
            switch# configure terminal
switch(config)# feature interface-vlan
switch(config)# interface vlan 5
switch(config-if)# management
switch(config-if)# copy running-config startup-config
switch(config-if)#

            The following example shows how to remove the management function from an SVI:

            switch# configure terminal
switch(config)# interface vlan 5
switch(config-if)# no management
switch(config-if)# copy running-config startup-config
switch(config-if)#

            Configuring VTP

            You can enable and configure VTP. If you enable VTP, you must configure either version 1 or version 2. If you are using VTP in a Token Ring environment, you must use version 2.

            Procedure
               Command or ActionPurpose
              Step 1switch# configure terminal 

              Enters global configuration mode.

               
              Step 2 switch(config)# feature vtp  

              Enables VTP on the device. The default is disabled.

               
              Step 3 switch(config)# vtp domain domain-name  

              Specifies the name of the VTP domain that you want this device to join. The default is blank.

               
              Step 4 switch(config)# vtp version {1 | 2}  

              Sets the VTP version that you want to use. The default is version 1.

               
              Step 5 switch(config)# vtp file file-name  

              Specifies the ASCII filename of the IFS file system file where the VTP configuration is stored.

               
              Step 6 switch(config)# vtp password password-value  

              Specifies the password for the VTP administrative domain.

               
              Step 7 switch(config)# exit  

              Exits the configuration submode.

               
              Step 8 switch# show vtp status   (Optional)

              Displays information about the VTP configuration on the device, such as the version, mode, and revision number.

               
              Step 9 switch# show vtp counters   (Optional)

              Displays information about VTP advertisement statistics on the device.

               
              Step 10 switch# show vtp interface   (Optional)

              Displays the list of VTP-enabled interfaces.

               
              Step 11 switch# show vtp password   (Optional)

              Displays the password for the management VTP domain.

               
              Step 12 switch# copy running-config startup-config   (Optional)

              Copies the running configuration to the startup configuration.

               

              This example shows how to configure VTP for the device: 

              switch# configure terminal
switch(config)# feature vtp
switch(config)# vtp domain accounting
switch(config)# vtp version 2
switch(config)# exit
switch#

              This example shows the VTP status and that the switch is capable of supporting Version 2 and that the switch is running Version 1: 

              switch(config)# show vtp status
VTP Status Information
----------------------
VTP Version                     : 2 (capable)
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 502
VTP Operating Mode              : Transparent
VTP Domain Name                 :
VTP Pruning Mode                : Disabled (Operationally Disabled)
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 Digest                      : 0xF5 0xF1 0xEC 0xE7 0x29 0x0C 0x2D 0x01
Configuration last modified by 60.10.10.1 at 0-0-00 00:00:00
VTP version running             : 1

              Verifying 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).

              Feature History for VLANs

              Feature Name

              Release

              Feature Information

              CISCO-VTP-MIB

              5.0(3)U4(1)

              Support for this MIB object was added.