Configuring VLANs

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Prerequisites for VLANs

The following are prerequisites and considerations for configuring VLANs:

  • To configure VLAN through the Web UI, you must change the Virtual Terminal (VTY) lines to 50. Web UI uses VTY lines for processing HTTP requests. At times, when multiple connections are open, the default VTY lines of 15 set by the device gets exhausted. Therefore, you must change the VTY lines to 50 before using the Web UI.


    Note
    To increase the VTY lines in a device, run the following command in the configuration mode: 
    Device#configure terminal
	Device(config)#service tcp-keepalives in
	Device(config)#service tcp-keepalives out

	Device#configure terminal
	Device(config)#line vty 16-50

  • Before you create VLANs, you must decide whether to use VLAN Trunking Protocol (VTP) to maintain global VLAN configuration for your network.

  • If you plan to configure many VLANs on the switch and to not enable routing, you can set the Switch Database Management (SDM) feature to the VLAN template, which configures system resources to support the maximum number of unicast MAC addresses.

  • Switches running the LAN Base feature set support only static routing on SVIs.

  • A VLAN should be present in the switch to be able to add it to the VLAN group.

Restrictions for VLANs

The following are restrictions for VLANs:

  • The switch supports up to 1005 normal and extended range VLANs when running the IP base or IP services feature set. It supports up to 255 VLANs when running the LAN Base feature set. However, the number of routed ports, switch virtual interfaces (SVIs), and other configured features affects the use of the switch hardware.

  • The switch supports IEEE 802.1Q trunking methods for sending VLAN traffic over Ethernet ports.

  • Configuring an interface VLAN router's MAC address is not supported. The interface VLAN already has an MAC address assigned by default.

  • Private VLANs are not supported on the switch.

Information About VLANs

Logical Networks

A VLAN is a switched network that is logically segmented by function, project team, 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 the 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 or a switch supporting fallback bridging. Because a VLAN is considered a separate logical network, it contains its own bridge Management Information Base (MIB) information and can support its own implementation of spanning tree.

VLANs are often associated with IP subnetworks. For example, all the end stations in a particular IP subnet belong to the same VLAN. Interface VLAN membership on the switch is assigned manually on an interface-by-interface basis. When you assign switch interfaces to VLANs by using this method, it is known as interface-based, or static, VLAN membership.

Traffic between VLANs must be routed.

The switch can route traffic between VLANs by using switch virtual interfaces (SVIs). An SVI must be explicitly configured and assigned an IP address to route traffic between VLANs.

Supported VLANs

The switch supports VLANs in VTP client, server, and transparent modes. VLANs are identified by a number from 1 to 4094. VLAN 1 is the default VLAN and is created during system initialization. VLAN IDs 1002 through 1005 are reserved for Token Ring and FDDI VLANs. All of the VLANs except 1002 to 1005 are available for user configuration.

There are 3 VTP versions. VTP version 1 and version 2 support only normal-range VLANs (VLAN IDs 1 to 1005). In these versions, the switch must be in VTP transparent mode when you create VLAN IDs from 1006 to 4094. VTP version 3 supports the entire VLAN range (VLANs 1 to 4094). Extended range VLANs (VLANs 1006 to 4094) are supported only in VTP version 3.

VLAN Port Membership Modes

You configure a port to belong to a VLAN by assigning a membership mode that specifies the kind of traffic the port carries and the number of VLANs to which it can belong.

This table lists the membership modes and membership and VTP characteristics.

Table 1. Port Membership Modes and Characteristics

Membership Mode

VLAN Membership Characteristics

VTP Characteristics

Static-access

A static-access port can belong to one VLAN and is manually assigned to that VLAN.

VTP is not required. If you do not want VTP to globally propagate information, set the VTP mode to transparent. To participate in VTP, there must be at least one trunk port on the switch or the switch stack connected to a trunk port of a second switch or switch stack.

Trunk ( IEEE 802.1Q)

A trunk port is a member of all VLANs by default, including extended-range VLANs, but membership can be limited by configuring the allowed-VLAN list. You can also modify the pruning-eligible list to block flooded traffic to VLANs on trunk ports that are included in the list.

VTP is recommended but not required. VTP maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs on a network-wide basis. VTP exchanges VLAN configuration messages with other switches over trunk links.

Dynamic access

A dynamic-access port can belong to one VLAN (VLAN ID 1 to 4094) and is dynamically assigned by a VMPS.

You can have dynamic-access ports and trunk ports on the same switch, but you must connect the dynamic-access port to an end station or hub and not to another switch.

VTP is required.

Configure the VMPS and the client with the same VTP domain name.

To participate in VTP, at least one trunk port on the switch or a switch stack must be connected to a trunk port of a second switch or switch stack.

When a port belongs to a VLAN, the switch learns and manages the addresses associated with the port on a per-VLAN basis.

VLAN Configuration Files

Configurations for VLAN IDs 1 to 1005 are written to the vlan.dat file (VLAN database), and you can display them by entering the show vlan privileged EXEC command. The vlan.dat file is stored in flash memory. If the VTP mode is transparent, they are also saved in the switch running configuration file.

You use the interface configuration mode to define the port membership mode and to add and remove ports from VLANs. The results of these commands are written to the running-configuration file, and you can display the file by entering the show running-config privileged EXEC command.

When you save VLAN and VTP information (including extended-range VLAN configuration information) in the startup configuration file and reboot the switch, the switch configuration is selected as follows:

  • If the VTP mode is transparent in the startup configuration, and the VLAN database and the VTP domain name from the VLAN database matches that in the startup configuration file, the VLAN database is ignored (cleared), and the VTP and VLAN configurations in the startup configuration file are used. The VLAN database revision number remains unchanged in the VLAN database.

  • If the VTP mode or domain name in the startup configuration does not match the VLAN database, the domain name and VTP mode and configuration for the VLAN IDs 1 to 1005 use the VLAN database information.

  • In VTP versions 1 and 2, if VTP mode is server, the domain name and VLAN configuration for VLAN IDs 1 to 1005 use the VLAN database information. VTP version 3 also supports VLANs 1006 to 4094.

  • From image 15.0(02)SE6, on vtp transparent and off modes, vlans get created from startup-config even if they are not applied to the interface.


Note

Ensure that you delete the vlan.dat file along with the configuration files before you reset the switch configuration using write erase command. This ensures that the switch reboots correctly on a reset.

Normal-Range VLAN Configuration Guidelines

Normal-range VLANs are VLANs with IDs from 1 to 1005.

Follow these guidelines when creating and modifying normal-range VLANs in your network:

  • Normal-range VLANs are identified with a number between 1 and 1001. VLAN numbers 1002 through 1005 are reserved for Token Ring and FDDI VLANs.

  • VLAN configurations for VLANs 1 to 1005 are always saved in the VLAN database. If the VTP mode is transparent, VTP and VLAN configurations are also saved in the switch running configuration file.

  • If the switch is in VTP server or VTP  transparent mode, you can add, modify or remove configurations for VLANs 2 to 1001 in the VLAN database. (VLAN IDs 1 and 1002 to 1005 are automatically created and cannot be removed.)

  • With VTP versions 1 and 2, the switch supports VLAN IDs 1006 through 4094 only in VTP transparent mode (VTP disabled). These are extended-range VLANs and configuration options are limited. Extended-range VLANs created in VTP transparent mode are not saved in the VLAN database and are not propagated. VTP version 3 supports extended range VLAN (VLANs 1006 to 4094) database propagation in VTP server mode. If extended VLANs are configured, you cannot convert from VTP version 3 to version 1 or 2.

  • Before you can create a VLAN, the switch must be in VTP server mode or VTP transparent mode. If the switch is a VTP server, you must define a VTP domain or VTP will not function.

  • The switch does not support Token Ring or FDDI media. The switch does not forward FDDI, FDDI-Net, TrCRF, or TrBRF traffic, but it does propagate the VLAN configuration through  VTP.

  • A fixed number of spanning tree instances are supported on the switch (See the datasheet for the latest information). If the switch has more active VLANs than the supported number of spaning tree instances, spanning tree is still enabled only on the supported number of VLANs and disabled on all remaining VLANs.

    If you have already used all available spanning-tree instances on a switch, adding another VLAN anywhere in the VTP domain creates a VLAN on that switch that is not running spanning-tree. If you have the default allowed list on the trunk ports of that switch (which is to allow all VLANs), the new VLAN is carried on all trunk ports. Depending on the topology of the network, this could create a loop in the new VLAN that would not be broken, particularly if there are several adjacent switches that all have run out of spanning-tree instances. You can prevent this possibility by setting allowed lists on the trunk ports of switches that have used up their allocation of spanning-tree instances.

    If the number of VLANs on the switch exceeds the number of supported spanning-tree instances, we recommend that you configure the IEEE 802.1s Multiple STP (MSTP) on your switch to map multiple VLANs to a single spanning-tree instance.

Extended-Range VLAN Configuration Guidelines

Extended-range VLANs are VLANs with IDs from 1006 to 4094.

Follow these guidelines when creating extended-range VLANs:

  • VLAN IDs in the extended range are not saved in the VLAN database and are not recognized by VTP unless the switch is running VTP version 3.

  • You cannot include extended-range VLANs in the pruning eligible range.

  • In VTP version 1 and 2, a switch must be in VTP transparent mode when you create extended-range VLANs. If VTP mode is server or client, an error message is generated, and the extended-range VLAN is rejected. VTP version 3 supports extended VLANs in server and transparent modes.

  • For VTP version 1 or 2, you can set the VTP mode to transparent in global configuration mode. You should save this configuration to the startup configuration so that the switch boots up in VTP transparent mode. Otherwise, you lose the extended-range VLAN configuration if the switch resets. If you create extended-range VLANs in VTP version 3, you cannot convert to VTP version 1 or 2.

  • . When the maximum number of spanning-tree instances are on the switch, spanning tree is disabled on any newly created VLANs. If the number of VLANs on the switch exceeds the maximum number of spanning-tree instances, we recommend that you configure the IEEE 802.1s Multiple STP (MSTP) on your switch to map multiple VLANs to a single spanning-tree instance.

  • Although the switch orswitch stack supports a total of 1005 (normal-range and extended-range) VLANs, the number of routed ports, SVIs, and other configured features affects the use of the switch hardware. If you try to create an extended-range VLAN and there are not enough hardware resources available, an error message is generated, and the extended-range VLAN is rejected.

Default Ethernet VLAN Configuration

The following table displays the default configuration for Ethernet VLANs.


Note

The switch supports Ethernet interfaces exclusively. Because FDDI and Token Ring VLANs are not locally supported, you only configure FDDI and Token Ring media-specific characteristics for VTP global advertisements to other switches.

Table 2. Ethernet VLAN Defaults and Range

Parameter

Default

Range

VLAN ID

1

1 to 4094.

Note 

Extended-range VLANs (VLAN IDs 1006 to 4094) are only saved in the VLAN database in VTP version 3.

VLAN name

VLANxxxx, where xxxx represents four numeric digits (including leading zeros) equal to the VLAN ID number

No range

IEEE 802.10 SAID

100001 (100000 plus the VLAN ID)

1 to 4294967294

IEEE 802.10 SAID

1500

576-18190

MTU Size

0

0 to 1005

How to Configure VLANs

How to Configure Normal-Range VLANs

You can set these parameters when you create a new normal-range VLAN or modify an existing VLAN in the VLAN database:

  • VLAN ID

  • VLAN name

  • VLAN type

    • Ethernet

    • Fiber Distributed Data Interface [FDDI]

    • FDDI network entity title [NET]

    • TrBRF or TrCRF

    • Token Ring

    • Token Ring-Net

  • VLAN state (active or suspended)

  • Security Association Identifier (SAID)

  • Bridge identification number for TrBRF VLANs

  • Ring number for FDDI and TrCRF VLANs

  • Parent VLAN number for TrCRF VLANs

  • Spanning Tree Protocol (STP) type for TrCRF VLANs

  • VLAN number to use when translating from one VLAN type to another

You can cause inconsistency in the VLAN database if you attempt to manually delete the vlan.dat file. If you want to modify the VLAN configuration, follow the procedures in this section.

Creating or Modifying an Ethernet VLAN

Each Ethernet VLAN in the VLAN database has a unique, 4-digit ID that can be a number from 1 to 1001. VLAN IDs 1002 to 1005 are reserved for Token Ring and FDDI VLANs. To create a normal-range VLAN to be added to the VLAN database, assign a number and name to the VLAN.


Note

With VTP version 1 and 2, if the switch is in VTP transparent mode, you can assign VLAN IDs greater than 1006, but they are not added to the VLAN database.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. vlan vlan-id
  4. name vlan-name
  5. mtu mtu-size
  6. remote-span
  7. end
  8. show vlan {name vlan-name | id vlan-id}
  9. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Switch> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode.

Step 3

vlan vlan-id

Example:


Switch(config)# vlan 20

Enters a VLAN ID, and enters VLAN configuration mode. Enter a new VLAN ID to create a VLAN, or enter an existing VLAN ID to modify that VLAN.

Note 

The available VLAN ID range for this command is 1 to 4094.

Step 4

name vlan-name

Example:


Switch(config-vlan)# name test20

(Optional) Enters a name for the VLAN. If no name is entered for the VLAN, the default is to append the vlan-id value with leading zeros to the word VLAN. For example, VLAN0004 is a default VLAN name for VLAN 4.

Step 5

mtu mtu-size

Example:


Switch(config-vlan)# mtu 256

(Optional) Changes the MTU size (or other VLAN characteristic).

Step 6

remote-span

Example:


Switch(config-vlan)# remote-span

(Optional) Configures the VLAN as the RSPAN VLAN for a remote SPAN session.

Step 7

end

Example:


Switch(config)# end

Returns to privileged EXEC mode.

Step 8

show vlan {name vlan-name | id vlan-id}

Example:


Switch# show vlan name test20 id 20

Verifies your entries.

Step 9

copy running-config startup-config

Example:


Switch# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Deleting a VLAN

When you delete a VLAN from a switch that is in VTP server mode, the VLAN is removed from the VLAN database for all switches in the VTP domain. When you delete a VLAN from a switch that is in VTP transparent mode, the VLAN is deleted only on that specific switch .

You cannot delete the default VLANs for the different media types: Ethernet VLAN 1 and FDDI or Token Ring VLANs 1002 to 1005.


Caution

When you delete a VLAN, any ports assigned to that VLAN become inactive. They remain associated with the VLAN (and thus inactive) until you assign them to a new VLAN.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. no vlan vlan-id
  4. end
  5. show vlan brief
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Switch> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode.

Step 3

no vlan vlan-id

Example:


Switch(config)# no vlan 4

Removes the VLAN by entering the VLAN ID.

Step 4

end

Example:


Switch(config)# end

Returns to privileged EXEC mode.

Step 5

show vlan brief

Example:


Switch# show vlan brief

Verifies the VLAN removal.

Step 6

copy running-config startup-config

Example:


Switch# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Assigning Static-Access Ports to a VLAN

You can assign a static-access port to a VLAN without having VTP globally propagate VLAN configuration information by disabling VTP (VTP transparent mode).

For the Cisco Catalyst 9500 Series Switches, if you are assigning a port on a cluster member switch to a VLAN, first use the rcommand privileged EXEC command to log in to the cluster member switch.

If you assign an interface to a VLAN that does not exist, the new VLAN is created.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface interface-id
  4. switchport mode access
  5. switchport access vlan vlan-id
  6. end
  7. show running-config interface interface-id
  8. show interfaces interface-id switchport
  9. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Switch> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode

Step 3

interface interface-id

Example:


Switch(config)# interface gigabitethernet2/0/1

Enters the interface to be added to the VLAN.

Step 4

switchport mode access

Example:


Switch(config-if)# switchport mode access

Defines the VLAN membership mode for the port (Layer 2 access port).

Step 5

switchport access vlan vlan-id

Example:


Switch(config-if)# switchport access vlan 2

Assigns the port to a VLAN. Valid VLAN IDs are 1 to 4094.

Step 6

end

Example:


Switch(config-if)# end

Returns to privileged EXEC mode.

Step 7

show running-config interface interface-id

Example:


Switch# show running-config interface gigabitethernet2/0/1

Verifies the VLAN membership mode of the interface.

Step 8

show interfaces interface-id switchport

Example:


Switch# show interfaces gigabitethernet2/0/1 switchport

Verifies your entries in the Administrative Mode and the Access Mode VLAN fields of the display.

Step 9

copy running-config startup-config

Example:


Switch# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

How to Configure Extended-Range VLANs

With VTP version 1 and version 2, when the switch is in VTP transparent mode (VTP disabled), you can create extended-range VLANs (in the range 1006 to 4094). VTP version supports extended-range VLANs in server or transparent move. Extended-range VLANs enable service providers to extend their infrastructure to a greater number of customers. The extended-range VLAN IDs are allowed for any switchport commands that allow VLAN IDs.

With VTP version 1 or 2, extended-range VLAN configurations are not stored in the VLAN database, but because VTP mode is transparent, they are stored in the switch running configuration file, and you can save the configuration in the startup configuration file by using the copy running-config startup-config privileged EXEC command. Extended-range VLANs created in VTP version 3 are stored in the VLAN database.

Creating an Extended-Range VLAN

In VTP version 1 or 2, if you enter an extended-range VLAN ID when the switch is not in VTP transparent mode, an error message is generated when you exit VLAN configuration mode, and the extended-range VLAN is not created.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. vlan vlan-id
  4. remote-span
  5. exit
  6. end
  7. show vlan id vlan-id
  8. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Switch> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode.

Step 3

vlan vlan-id

Example:


Switch(config)# vlan 2000
Switch(config-vlan)#

Enters an extended-range VLAN ID and enters VLAN configuration mode. The range is 1006 to 4094.

Step 4

remote-span

Example:


Switch(config-vlan)# remote-span

(Optional) Configures the VLAN as the RSPAN VLAN.

Step 5

exit

Example:


Switch(config-vlan)# exit
Switch(config)#

Returns to configuration mode.

Step 6

end

Example:


Switch(config)# end

Returns to privileged EXEC mode.

Step 7

show vlan id vlan-id

Example:


Switch# show vlan id 2000

Verifies that the VLAN has been created.

Step 8

copy running-config startup-config

Example:


Switch# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Where to Go Next

After configuring VLANs, you can configure the following:

  • VLAN Trunking Protocol (VTP)

  • VLAN trunks

Additional References

Standards and RFCs

Standard/RFC Title

RFC 1573

Evolution of the Interfaces Group of MIB-II

RFC 1757

Remote Network Monitoring Management

RFC 2021

SNMPv2 Management Information Base for the Transmission Control Protocol using SMIv2

MIBs

MIB MIBs Link

All the supported MIBs for this release.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

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