Cisco 7600 Series Cisco IOS Software Configuration Guide, 12.1E
Configuring VLANs
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Configuring VLANs

Table Of Contents

Configuring VLANs

Understanding How VLANs Work

VLAN Overview

VLAN Ranges

Configurable VLAN Parameters

Understanding Token Ring VLANs

Token Ring TrBRF VLANs

Token Ring TrCRF VLANs

VLAN Default Configuration

VLAN Configuration Guidelines and Restrictions

Restrictions

Guidelines

Configuring VLANs

VLAN Configuration Options

VLAN Configuration in Global Configuration Mode

VLAN Configuration in VLAN Database Mode

Creating or Modifying an Ethernet VLAN

Assigning a Layer 2 LAN Interface to a VLAN

Configuring the Internal VLAN Allocation Policy

Mapping 802.1Q VLANs to ISL VLANs


Configuring VLANs


This chapter describes how to configure VLANs on the Catalyst 6500 series switches.


Note For complete syntax and usage information for the commands used in this chapter, refer to the Catalyst 6500 Series Switch Cisco IOS Command Reference publication.


This chapter consists of these sections:

Understanding How VLANs Work

VLAN Default Configuration

VLAN Configuration Guidelines and Restrictions

Configuring VLANs

Understanding How VLANs Work

The following sections describe how VLANs work:

VLAN Overview

VLAN Ranges

Configurable VLAN Parameters

Understanding Token Ring VLANs

VLAN Overview

A VLAN is a group of end stations with a common set of requirements, independent of physical location. VLANs have the same attributes as a physical LAN but allow you to group end stations even if they are not located physically on the same LAN segment.

VLANs are usually associated with IP subnetworks. For example, all the end stations in a particular IP subnet belong to the same VLAN. Traffic between VLANs must be routed. LAN port VLAN membership is assigned manually on an port-by-port basis.

VLAN Ranges


Note You must enable the extended system ID to use 4096 VLANs (see the "Understanding the Bridge ID" section on page 15-3).


With Release 12.1(13)E and later releases, Catalyst 6500 series switches support 4096 VLANs in accordance with the IEEE 802.1Q standard. These VLANs are organized into several ranges; you use each range slightly differently. Some of these VLANs are propagated to other switches in the network when you use the VLAN Trunking Protocol (VTP). The extended-range VLANs are not propagated, so you must configure extended-range VLANs manually on each network device.

Table 9-1 describes the VLAN ranges.

Table 9-1 VLAN Ranges

VLANs
Range
Usage
Propagated
by VTP

0, 4095

Reserved

For system use only. You cannot see or use these VLANs.

1

Normal

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

Yes

2-1001

Normal

For Ethernet VLANs; you can create, use, and delete these VLANs.

Yes

1002-1005

Normal

Cisco defaults for FDDI and Token Ring. You cannot delete VLANs 1002-1005.

Yes

1006-4094

Extended

For Ethernet VLANs only.

No


The following information applies to VLAN ranges:

Layer 3 LAN ports, WAN interfaces and subinterfaces, and some software features use internal VLANs in the extended range. You cannot use an extended range VLAN that has been allocated for internal use.

With Release 12.1(13)E and later releases, to display the VLANs used internally, enter the show vlan internal usage command. With earlier releases, enter the show vlan internal usage and show cwan vlans commands.

With Release 12.1(13)E and later releases, you can configure ascending internal VLAN allocation (from 1006 and up) or descending internal VLAN allocation (from 4094 and down). In previous 12.1EX releases that support 4096 VLANs, internal VLANs are allocated from 1006 and up.

Switches running the Catalyst operating system do not support configuration of VLANs 1006-1024. If you configure VLANs 1006-1024, ensure that the VLANs do not extend to any switches running Catalyst software.

You must enable the extended system ID to use extended range VLANs (see the "Understanding the Bridge ID" section on page 15-3).

Configurable VLAN Parameters


NoteEthernet VLAN 1 uses only default values.

Except for the VLAN name, Ethernet VLANs 1006 through 4094 use only default values.

With Release 12.1(13)E and later releases, you can configure the VLAN name for Ethernet VLANs 1006 through 4094.


You can configure the following parameters for VLANs 2 through 1001:

VLAN name

VLAN type (Ethernet, FDDI, FDDI network entity title [NET], TrBRF, or TrCRF)

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

Understanding Token Ring VLANs

The following section describes the two Token Ring VLAN types supported on network devices running VTP version 2:

Token Ring TrBRF VLANs

Token Ring TrCRF VLANs


Note Catalyst 6500 series switches do not support Inter-Switch Link (ISL)-encapsulated Token Ring frames. When a Catalyst 6500 series switch is configured as a VTP server, you can configure Token Ring VLANs from the switch.


Token Ring TrBRF VLANs

Token Ring Bridge Relay Function (TrBRF) VLANs interconnect multiple Token Ring Concentrator Relay Function (TrCRF) VLANs in a switched Token Ring network (see Figure 9-1). The TrBRF can be extended across network devices interconnected with trunk links. The connection between the TrCRF and the TrBRF is referred to as a logical port.

Figure 9-1 Interconnected Token Ring TrBRF and TrCRF VLANs

For source routing, the Catalyst 6500 series switch appears as a single bridge between the logical rings. The TrBRF can function as a source-route bridge (SRB) or a source-route transparent (SRT) bridge running either the IBM or IEEE STP. If an SRB is used, you can define duplicate MAC addresses on different logical rings.

The Token Ring software runs an instance of STP for each TrBRF VLAN and each TrCRF VLAN. For TrCRF VLANs, STP removes loops in the logical ring. For TrBRF VLANs, STP interacts with external bridges to remove loops from the bridge topology, similar to STP operation on Ethernet VLANs.


Caution Certain parent TrBRF STP and TrCRF bridge mode configurations can place the logical ports (the connection between the TrBRF and the TrCRF) of the TrBRF in a blocked state. For more information, see the "VLAN Configuration Guidelines and Restrictions" section.

To accommodate IBM System Network Architecture (SNA) traffic, you can use a combination of SRT and SRB modes. In a mixed mode, the TrBRF determines that some ports (logical ports connected to TrCRFs) operate in SRB mode while other ports operate in SRT mode

Token Ring TrCRF VLANs

Token Ring Concentrator Relay Function (TrCRF) VLANs define port groups with the same logical ring number. You can configure two types of TrCRFs in your network: undistributed and backup.

TrCRFs typically are undistributed, which means each TrCRF is limited to the ports on a single network device. Multiple undistributed TrCRFs on the same or separate network devices can be associated with a single parent TrBRF (see Figure 9-2). The parent TrBRF acts as a multiport bridge, forwarding traffic between the undistributed TrCRFs.


Note To pass data between rings located on separate network devices, you can associate the rings to the same TrBRF and configure the TrBRF for an SRB.


Figure 9-2 Undistributed TrCRFs

By default, Token Ring ports are associated with the default TrCRF (VLAN 1003, trcrf-default), which has the default TrBRF (VLAN 1005, trbrf-default) as its parent. In this configuration, a distributed TrCRF is possible (see Figure 9-3), and traffic is passed between the default TrCRFs located on separate network devices if the network devices are connected through an ISL trunk.

Figure 9-3 Distributed TrCRF

Within a TrCRF, source-route switching forwards frames based on either MAC addresses or route descriptors. The entire VLAN can operate as a single ring, with frames switched between ports within a single TrCRF.

You can specify the maximum hop count for All-Routes and Spanning Tree Explorer frames for each TrCRF. When you specify the maximum hop count, you limit the maximum number of hops an explorer is allowed to traverse. If a port determines that the explorer frame it is receiving has traversed more than the number of hops specified, it does not forward the frame. The TrCRF determines the number of hops an explorer has traversed by the number of bridge hops in the route information field.

If the ISL connection between network devices fails, you can use a backup TrCRF to configure an alternate route for traffic between undistributed TrCRFs. Only one backup TrCRF for a TrBRF is allowed, and only one port per network device can belong to a backup TrCRF.

If the ISL connection between the network devices fails, the port in the backup TrCRF on each affected network device automatically becomes active, rerouting traffic between the undistributed TrCRFs through the backup TrCRF. When the ISL connection is reestablished, all but one port in the backup TrCRF is disabled. Figure 9-4 illustrates the backup TrCRF.

Figure 9-4 Backup TrCRF

VLAN Default Configuration

Tables 9-2 through 9-6 show the default configurations for the different VLAN media types.

Table 9-2 Ethernet VLAN Defaults and Ranges 

Parameter
Default
Range

VLAN ID

1

1-4094

VLAN name

"default" for VLAN 1
"VLANvlan_ID" for other Ethernet VLANs

802.10 SAID

10vlan_ID

100001-104094

MTU size

1500

1500-18190

Translational bridge 1

0

0-1005

Translational bridge 2

0

0-1005

VLAN state

active

active, suspend

Pruning eligibility

VLANs 2-1001 are pruning eligible; VLANs 1006-4094 are not pruning eligible.


Table 9-3 FDDI VLAN Defaults and Ranges 

Parameter
Default
Range

VLAN ID

1002

1-1005

VLAN name

"fddi-default"

802.10 SAID

101002

1-4294967294

MTU size

1500

1500-18190

Ring number

0

1-4095

Parent VLAN

0

0-1005

Translational bridge 1

0

0-1005

Translational bridge 2

0

0-1005

VLAN state

active

active, suspend


Table 9-4 Token Ring (TrCRF) VLAN Defaults and Ranges 

Parameter
Default
Range

VLAN ID

1003

1-1005

VLAN name

"token-ring-default"

802.10 SAID

101003

1-4294967294

Ring Number

0

1-4095

MTU size

VTPv1 default 1500
VTPv2 default 4472

1500-18190

Translational bridge 1

0

0-1005

Translational bridge 2

0

0-1005

VLAN state

active

active, suspend

Bridge mode

srb

srb, srt

ARE max hops

7

0-13

STE max hops

7

0-13

Backup CRF

disabled

disable; enable


Table 9-5 FDDI-Net VLAN Defaults and Ranges 

Parameter
Default
Range

VLAN ID

1004

1-1005

VLAN name

"fddinet-default"

802.10 SAID

101004

1-4294967294

MTU size

1500

1500-18190

Bridge number

1

0-15

STP type

ieee

auto, ibm, ieee

VLAN state

active

active, suspend


Table 9-6 Token Ring (TrBRF) VLAN Defaults and Ranges 

Parameter
Default
Range

VLAN ID

1005

1-1005

VLAN name

"trnet-default"

802.10 SAID

101005

1-4294967294

MTU size

VTPv1 1500; VTPv2 4472

1500-18190

Bridge number

1

0-15

STP type

ibm

auto, ibm, ieee

VLAN state

active

active, suspend


VLAN Configuration Guidelines and Restrictions

Follow these guidelines and restrictions when creating and modifying VLANs in your network:

Restrictions

Supervisor engine redundancy does not support nondefault VLAN data file names or locations. Do not enter the vtp file file_name command on a switch that has a redundant supervisor engine.

RPR+ redundancy (see Chapter 5, "Configuring RPR and RPR+ Supervisor Engine Redundancy") does not support a configuration entered in VLAN database mode. Use global configuration mode with RPR+ redundancy.

You can configure extended-range VLANs only in global configuration mode. You cannot configure extended-range VLANs in VLAN database mode. See the "VLAN Configuration Options" section.

The Cisco IOS end command is not supported in VLAN database mode.

You cannot enter Ctrl-Z to exit VLAN database mode.

Catalyst 6500 series switches do not support Token Ring or FDDI media. The switch does not forward FDDI, FDDI-Net, TrCRF, or TrBRF traffic, but it can propagate the VLAN configuration through VTP.

In a Token Ring environment, the logical interfaces (the connection between the TrBRF and the TrCRF) of the TrBRF are placed in a blocked state if either of these conditions exists:

The TrBRF is running the IBM STP, and the TrCRF is in SRT mode.

The TrBRF is running the IEEE STP, and the TrCRF is in SRB mode.

Guidelines

Before installing a redundant supervisor engine, enter the no vtp file command to return to the default configuration.

Before you can create a VLAN, the Catalyst 6500 series switch must be in VTP server mode or VTP transparent mode. For information on configuring VTP, see Chapter 8, "Configuring VTP."

The VLAN configuration is stored in the vlan.dat file, which is stored in nonvolatile memory. You can cause inconsistency in the VLAN database if you manually delete the vlan.dat file. If you want to modify the VLAN configuration or VTP, use the commands described in this guide and in the Catalyst 6500 Series Switch Cisco IOS Command Reference publication.

To do a complete backup of your configuration, include the vlan.dat file in the backup.

When a Catalyst 6500 series switch is configured as a VTP server, you can configure FDDI and Token Ring VLANs from the switch.

You must configure a TrBRF before you configure the TrCRF (the parent TrBRF VLAN you specify must exist).

Configuring VLANs

These sections describe how to configure VLANs:

VLAN Configuration Options

Creating or Modifying an Ethernet VLAN

Assigning a Layer 2 LAN Interface to a VLAN

Configuring the Internal VLAN Allocation Policy

Mapping 802.1Q VLANs to ISL VLANs


NoteWith releases 12.1(11b)E and later, when you are in configuration mode you can enter EXEC mode commands by entering the do keyword before the EXEC mode command.

VLANs support a number of parameters that are not discussed in detail in this section. For complete information, refer to the Catalyst 6500 Series Switch Cisco IOS Command Reference publication.


VLAN Configuration Options

These sections describe the VLAN configuration options:

VLAN Configuration in Global Configuration Mode

VLAN Configuration in VLAN Database Mode

VLAN Configuration in Global Configuration Mode


Note Releases 12.1(11b)E and later support VLAN configuration in global configuration mode.


If the switch is in VTP server or transparent mode (see the "Configuring VTP" section on page 8-6), you can configure VLANs in global and config-vlan configuration modes. When you configure VLANs in global and config-vlan configuration modes, the VLAN configuration is saved in the vlan.dat files. To display the VLAN configuration, enter the show vlan command.

If the switch is in VLAN transparent mode, use the copy running-config startup-config command to save the VLAN configuration to the startup-config file. After you save the running configuration as the startup configuration, use the show running-config and show startup-config commands to display the VLAN configuration.


NoteWhen the switch boots, if the VTP domain name and VTP mode in the startup-config and vlan.dat files do not match, the switch uses the configuration in the vlan.dat file.

You can configure extended-range VLANs only in global configuration mode. You cannot configure extended-range VLANs in VLAN database mode.


VLAN Configuration in VLAN Database Mode


Note You cannot configure extended-range VLANs in VLAN database mode. You can configure extended-range VLANs only in global configuration mode. RPR+ redundancy does not support configuration entered in VLAN database mode. Use global configuration mode with RPR+ redundancy.


If the switch is in VTP server or transparent mode, you can configure VLANs in the VLAN database mode. When you configure VLANs in VLAN database mode, the VLAN configuration is saved in the vlan.dat files. To display the VLAN configuration, enter the show vlan command.

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

Creating or Modifying an Ethernet VLAN

User-configured VLANs have unique IDs from 1 to 4094, except for reserved VLANs (see Table 9-1). Enter the vlan command with an unused ID to create a VLAN. Enter the vlan command for an existing VLAN to modify the VLAN (you cannot modify an existing VLAN that is being used by a Layer 3 port or a software feature).

See the "VLAN Default Configuration" section for the list of default parameters that are assigned when you create a VLAN. If you do not specify the VLAN type with the media keyword, the VLAN is an Ethernet VLAN.

To create or modify a VLAN, perform this task:

 
Command
Purpose

Step 1 

Router# configure terminal

or 

Router# vlan database

Enters VLAN configuration mode.

Step 2 

Router(config)# vlan vlan_ID{[-vlan_ID]|[,vlan_ID])

Router(config-vlan)#
or 

Router(vlan)# vlan vlan_ID

Creates or modifies an Ethernet VLAN, a range of Ethernet VLANs, or several Ethernet VLANs specified in a comma-separated list (do not enter space characters).

Router(config)# no vlan vlan_ID

Router(config-vlan)#

or 

Router(vlan)# no vlan vlan_ID

Deletes a VLAN.

Step 3 

Router(config-vlan)# end

or 

Router(vlan)# exit

Updates the VLAN database and returns to privileged EXEC mode.

Step 4 

Router# show vlan [id | name] vlan

Verifies the VLAN configuration.

When you create or modify an Ethernet VLAN, note the following syntax information:

Releases 12.1(11b)E and later support VLAN configuration in global configuration mode.

Releases 12.1(13)E and later support extended-range VLANs.

RPR+ redundancy does not support a configuration entered in VLAN database mode. Use global configuration mode with RPR+ redundancy.

Because Layer 3 ports and some software features require internal VLANs allocated from 1006 and up, configure extended-range VLANs starting with 4094.

You can configure extended-range VLANs only in global configuration mode. You cannot configure extended-range VLANs in VLAN database mode.

Layer 3 ports and some software features use extended-range VLANs. If the VLAN you are trying to create or modify is being used by a Layer 3 port or a software feature, the switch displays a message and does not modify the VLAN configuration.

When deleting VLANs, note the following syntax information:

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

When you delete a VLAN, any LAN ports configured as access ports assigned to that VLAN become inactive. The ports remain associated with the VLAN (and inactive) until you assign them to a new VLAN.

This example shows how to create an Ethernet VLAN in global configuration mode and verify the configuration:

Router# configure terminal
Router(config)# vlan 3 
Router(config-vlan)# end 
Router# show vlan id 3 

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
3    VLAN0003                         active    

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
3    enet  100003     1500  -      -      -        -    -        0      0   

Primary Secondary Type              Interfaces
------- --------- ----------------- ------------------------------------------

This example shows how to create an Ethernet VLAN in VLAN database mode:

Router# vlan database 
Router(vlan)# vlan 3 
VLAN 3 added:
    Name: VLAN0003
Router(vlan)# exit 
APPLY completed.
Exiting....

This example shows how to verify the configuration:

Router# show vlan name VLAN0003 
VLAN Name                             Status    Ports
---- -------------------------------- --------- ---------------------
3    VLAN0003                         active
 
VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- ------ ------
3    enet  100003     1500  -      -      -        -    0      0
Router# 

Assigning a Layer 2 LAN Interface to a VLAN

A VLAN created in a management domain remains unused until you assign one or more LAN ports to the VLAN.


Note Make sure you assign LAN ports to a VLAN of the appropriate type. Assign Ethernet ports to Ethernet-type VLANs.


To assign one or more LAN ports to a VLAN, complete the procedures in the "Configuring LAN Interfaces for Layer 2 Switching" section on page 7-7.

Configuring the Internal VLAN Allocation Policy

Internal VLAN allocation policy is supported in Release 12.1(13)E and later releases. For more information about VLAN allocation, see the "VLAN Ranges" section.


Note The internal VLAN allocation policy is applied only following a reload.


To configure the internal VLAN allocation policy, perform this task:

 
Command
Purpose

Step 1 

Router(config)# vlan internal allocation policy {ascending | descending}

Configures the internal VLAN allocation policy.

Router(config)# no vlan internal allocation policy

Returns to the default (ascending).

Step 2 

Router(config)# end

Exits configuration mode.

Step 3 

Router# reload

Applies the new internal VLAN allocation policy.


Caution You do not need to enter the reload command immediately. Enter the reload command during a planned maintenance window.

When you configure the internal VLAN allocation policy, note the following syntax information:

Enter the ascending keyword to allocate internal VLANs from 1006 and up.

Enter the descending keyword to allocate internal VLAN from 4094 and down.

This example shows how to configure descending as the internal VLAN allocation policy:

Router# configure terminal 
Router(config)# vlan internal allocation policy descending 

Mapping 802.1Q VLANs to ISL VLANs

The valid range of user-configurable ISL VLANs is 1 through 1001 and 1006 through 4094. The valid range of VLANs specified in the IEEE 802.1Q standard is 1 to 4094. You can map 802.1Q VLAN numbers to ISL VLAN numbers.

802.1Q VLANs in the range 1 through 1001 and 1006 through 4094 are automatically mapped to the corresponding ISL VLAN. 802.1Q VLAN numbers corresponding to reserved VLAN numbers must be mapped to an ISL VLAN in order to be recognized and forwarded by Cisco network devices.

These restrictions apply when mapping 802.1Q VLANs to ISL VLANs:

You can configure up to eight 802.1Q-to-ISL VLAN mappings on the Catalyst 6500 series switch.

You can only map 802.1Q VLANs to Ethernet-type ISL VLANs.

Do not enter the native VLAN of any 802.1Q trunk in the mapping table.

When you map an 802.1Q VLAN to an ISL VLAN, traffic on the 802.1Q VLAN corresponding to the mapped ISL VLAN is blocked. For example, if you map 802.1Q VLAN 1007 to ISL VLAN 200, traffic on 802.1Q VLAN 200 is blocked.

VLAN mappings are local to each Catalyst 6500 series switch. Make sure you configure the same VLAN mappings on all appropriate network devices.

To map an 802.1Q VLAN to an ISL VLAN, perform this task:

 
Command
Purpose

Step 1 

Router(config)# vlan mapping dot1q dot1q_vlan isl isl_vlan

Maps an 802.1Q VLAN to an ISL Ethernet VLAN. The valid range for dot1q_vlan is 1001 to 4094. The valid range for isl_vlan is the same.

Router(config)# no vlan mapping dot1q {all | dot1q_vlan}

Deletes the mapping.

Step 2 

Router(config)# end

Exits configuration mode.

Step 3 

Router# show vlan

Verifies the VLAN mapping.

This example shows how to map 802.1Q VLAN 1003 to ISL VLAN 200:

Router# configure terminal 
Router(config)# vlan mapping dot1q 1003 isl 200 
Router(config)# end 
Router# 

This example shows how to verify the configuration:

Router# show vlan 
<...output truncated...>
802.1Q Trunk Remapped VLANs:
802.1Q VLAN    ISL VLAN
-----------   -----------
   1003          200