Catalyst 4500 Series Switch Cisco IOS Software Configuration Guide, 12.2(25)EWA

Understanding and Configuring VLANs

This chapter describes VLANs on Catalyst 4500 series switches. It also describes how to enable the VLAN Trunking Protocol (VTP) and to configure the Catalyst 4500 series switch as a VMPS client.

This chapter includes the following major sections:

•VLANs

•VLAN Trunking Protocol

•VLAN Membership Policy Server

VLANs

This section includes the following major subsections:

•Overview of VLANs

•VLAN Configuration Guidelines and Restrictions

•VLAN Default Configuration

•Configuring VLANs

Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it is located in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

Overview of VLANs

A VLAN is a group of devices on one or more LANs that are configured to communicate as if they were attached to the same wire, when in fact they are located on a number of different LAN segments. Because VLANs are based on logical instead of physical connections, they are extremely flexible.

VLANs define broadcast domains in a Layer 2 network. A broadcast domain is the set of all devices that will receive broadcast frames originating from any device within the set. Broadcast domains are typically bounded by routers because routers do not forward broadcast frames. Layer 2 switches create broadcast domains based on the configuration of the switch. Switches are multiport bridges that allow you to create multiple broadcast domains. Each broadcast domain is like a distinct virtual bridge within a switch.

You can define one or many virtual bridges within a switch. Each virtual bridge you create in the switch defines a new broadcast domain (VLAN). Traffic cannot pass directly to another VLAN (between broadcast domains) within the switch or between two switches. To interconnect two different VLANs, you must use routers or Layer 3 switches. See the "Overview of Layer 3 Interfaces" section on page 22-1 for information on inter-VLAN routing on Catalyst 4500 series switches.

Figure 10-1 shows an example of three VLANs that create logically defined networks.

Figure 10-1 Sample VLANs

VLANs are often associated with IP subnetworks. For example, all of the end stations in a particular IP subnet belong to the same VLAN. Traffic between VLANs must be routed. You must assign LAN interface VLAN membership on an interface-by-interface basis (this is known as interface-based or static VLAN membership).

You can set the following parameters when you create a VLAN in the management domain:

•VLAN number

•VLAN name

•VLAN type

•VLAN state (active or suspended)

•Maximum transmission unit (MTU) for the VLAN

•Security Association Identifier (SAID)

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

Note When the software translates from one VLAN type to another, it requires a different VLAN number for each media type.

VLAN Configuration Guidelines and Restrictions

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

•Before creating a VLAN, put the Catalyst 4500 series switch in VTP server mode or VTP transparent mode. If the Catalyst 4500 series switch is a VTP server, you must define a VTP domain. For information on configuring VTP, see Chapter 27, "Understanding and Configuring VTP."

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

•You cannot use Ctrl-Z to exit VLAN database mode.

VLAN Ranges

Note You must enable the extended system ID to use 4094 VLANs. See the "Understanding the Bridge ID" section on page 13-2.

With Cisco IOS Release 12.2(25)EWA and later, Catalyst 4500 series switches support 4096 VLANs in compliance with the IEEE 802.1Q standard. These VLANs are organized into three ranges: reserved, normal, and extended.

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 10-1 describes the uses for VLAN ranges.

Configurable Normal-Range VLAN Parameters

Note Ethernet VLANs 1 and 1006 through 4094 use only default values.

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

•VLAN name

•VLAN type

•VLAN state (active or suspended)

•SAID

•STP type for VLANs

VLAN Default Configuration

Table 10-2 shows the default VLAN configuration values.

Note Catalyst 4500 series switches do 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 via VTP. The software reserves parameters for these media types, but they are not truly supported.

Configuring VLANs

Note Before you configure VLANs, you must use VLAN Trunking Protocol (VTP) to maintain global VLAN configuration information for your network. For complete information on VTP, see Chapter 27, "Understanding and Configuring VTP."

Note VLANs support a number of parameters that are not discussed in detail in this section. For complete information, refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference.

Note 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 the following sections and in the Catalyst 4500 Series Switch Cisco IOS Command Reference.

The following sections describe how to configure VLANs:

•Configuring VLANs in Global Configuration Mode

•Configuring VLANs in VLAN Database Mode

•Assigning a Layer 2 LAN Interface to a VLAN

Configuring VLANs in Global Configuration Mode

If the switch is in VTP server or transparent mode (see the "Configuring VTP" section on page 27-6), you can configure VLANs in global and VLAN configuration modes. When you configure VLANs in global and config-vlan configuration modes, the VLAN configuration is saved in the vlan.dat files, not the running-config or startup-config 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, the show running-config and show startup-config commands display the VLAN configuration.

Note When 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 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 contents of the file by entering the show running-config command.

User-configured VLANs have unique IDs from 1 to 4094. To create a VLAN, enter the vlan command with an unused ID. To verify whether a particular ID is in use, enter the show vlan id ID command. To modify a VLAN, enter the vlan command for an existing VLAN.

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

To create a VLAN, perform this task:

Switch# configure terminal 

Switch(config)# vlan vlan_ID 

Switch(config-vlan)#

Switch(config-vlan)# end 

Switch# show vlan [id | name] vlan_name

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

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

•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.

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

Switch# configure terminal

Switch(config)# vlan 3 

Switch(config-vlan)# end 

Switch# 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

------- --------- ----------------- -------------------------------------------

Switch#

Configuring VLANs in VLAN Database Mode

When 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 file, not the running-config or startup-config files. To display the VLAN configuration, enter the show running-config vlan command.

User-configurable VLANs have unique IDs from 1 to 4094. Database mode supports configuration of IDs from 1 to 1001, but not the extended addresses from 1006 to 4094. To create a VLAN, enter the vlan command with an unused ID. To verify whether a particular ID is in use, enter the show vlan id ID command. To modify a VLAN, enter the vlan command for an existing VLAN.

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

To create a VLAN, perform this task:

Switch# vlan database

Switch(vlan)# vlan vlan_ID 

Switch(vlan)# exit 

Switch# show vlan [id | name] vlan_name 

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

Switch# vlan database 

Switch(vlan)# vlan 3 

VLAN 3 added:

    Name: VLAN0003

Switch(vlan)# exit 

APPLY completed.

Exiting....

Switch# 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

Switch# 

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 interfaces to the VLAN.

Note Make sure you assign LAN interfaces to a VLAN of the proper type. Assign Fast Ethernet, Gigabit Ethernet, and 10-Gigabit Ethernet interfaces to Ethernet-type VLANs.

To assign one or more LAN interfaces to a VLAN, complete the procedures in the "Configuring Ethernet Interfaces for Layer 2 Switching" section on page 11-5.

VLAN Trunking Protocol

This section describes the VLAN Trunking Protocol (VTP) on the Catalyst 4500 series switches.

This section includes the following major subsections:

•Overview of VTP

•VTP Configuration Guidelines and Restrictions

•VTP Default Configuration

•Configuring VTP

Overview of VTP

VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs within a VTP domain. A VTP domain (also called a VLAN management domain) is made up of one or more network devices that share the same VTP domain name and that are interconnected with trunks. VTP minimizes misconfigurations and configuration inconsistencies that can result in a number of problems, such as duplicate VLAN names, incorrect VLAN-type specifications, and security violations.

Before you create VLANs, you must decide whether you want to use VTP in your network. With VTP, you can make configuration changes centrally on one or more network devices and have those changes automatically communicated to all the other network devices in the network. For details on configuring VLANs, see VLANs

These sections describe how VTP works:

•Understanding the VTP Domain

•Understanding VTP Modes

•Understanding VTP Advertisements

•Understanding VTP Version 2

•Understanding VTP Pruning

Understanding the VTP Domain

A VTP domain is made up of one or more interconnected network devices that share the same VTP domain name. A network device can be configured to be in only one VTP domain. You make global VLAN configuration changes for the domain using either the command-line interface (CLI) or Simple Network Management Protocol (SNMP).

By default, the Catalyst 4500 series switch is in VTP transparent mode and is in the no-management domain state until the switch receives an advertisement for a domain over a trunk link or you configure a management domain. You cannot create or modify VLANs on a VTP server until the management domain name is specified or learned.

If the switch receives a VTP advertisement over a trunk link, it inherits the management domain name and the VTP configuration revision number. The switch ignores advertisements with a different management domain name or an earlier configuration revision number.

If you configure the switch as VTP transparent, you can create and modify VLANs, but the changes affect only the individual switch.

When you make a change to the VLAN configuration on a VTP server, the change is propagated to all network devices in the VTP domain. VTP advertisements are transmitted out all Inter-Switch Link (ISL) and IEEE 802.1Q trunk connections.

VTP maps VLANs dynamically across multiple LAN types with unique names and internal index associations. Mapping eliminates unnecessary device administration for network administrators.

Understanding VTP Modes

You can configure a Catalyst 4500 series switch to operate in any one of these VTP modes:

•Server—In VTP server mode, you can create, modify, and delete VLANs and specify other configuration parameters (such as VTP version and VTP pruning) for the entire VTP domain. VTP servers advertise their VLAN configuration to other network devices in the same VTP domain and synchronize their VLAN configuration with other network devices based on advertisements received over trunk links. VTP server is the default mode.

•Client—VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client.

•Transparent—VTP transparent network devices do not participate in VTP. A VTP transparent network device does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. However, in VTP version 2, transparent network devices do forward VTP advertisements that they receive on their trunking LAN interfaces.

Note Catalyst 4500 series switches automatically change from VTP server mode to VTP client mode if the switch detects a failure while writing configuration to NVRAM. If this happens, the switch cannot be returned to VTP server mode until the NVRAM is functioning.

Understanding VTP Advertisements

Each network device in the VTP domain sends periodic advertisements out each trunking LAN interface to a reserved multicast address. VTP advertisements are received by neighboring network devices, which update their VTP and VLAN configurations as necessary.

The following global configuration information is distributed in VTP advertisements:

•VLAN IDs (ISL and 802.1Q)

•Emulated LAN names (for ATM LANE)

•802.10 SAID values (FDDI)

•VTP domain name

•VTP configuration revision number

•VLAN configuration, including maximum transmission unit (MTU) size for each VLAN

•Frame format

Understanding VTP Version 2

If you use VTP in your network, you must decide whether to use VTP version 1 or version 2.

Note Catalyst 4500 series switches do not support Token Ring or FDDI media. The switch does not forward FDDI, FDDI-Net, Token Ring Concentrator Relay Function [TrCRF], or Token Ring Bridge Relay Function [TrBRF] traffic, but it does propagate the VLAN configuration via VTP.

VTP version 2 supports the following features, which are not supported in version 1:

•Token Ring support—VTP version 2 supports Token Ring LAN switching and VLANs (TrBRF and TrCRF).

•Unrecognized Type-Length-Value (TLV) Support—A VTP server or client propagates configuration changes to its other trunks, even for TLVs it is not able to parse. The unrecognized TLV is saved in NVRAM.

•Version-Dependent Transparent Mode—In VTP version 1, a VTP transparent network device inspects VTP messages for the domain name and version, and forwards a message only if the version and domain name match. Because only one domain is supported in the supervisor engine software, VTP version 2 forwards VTP messages in transparent mode, without checking the version.

•Consistency Checks—In VTP version 2, VLAN consistency checks (such as VLAN names and values) are performed only when you enter new information through the CLI or SNMP. Consistency checks are not performed when new information is obtained from a VTP message or when information is read from NVRAM. If the digest on a received VTP message is correct, its information is accepted without consistency checks.

Understanding VTP Pruning

VTP pruning enhances network bandwidth use by reducing unnecessary flooded traffic, such as broadcast, multicast, and unicast packets. VTP pruning increases available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to access the appropriate network devices. By default, VTP pruning is disabled.

For VTP pruning to be effective, all devices in the management domain must either support VTP pruning or, on devices that do not support VTP pruning, you must manually configure the VLANs allowed on trunks.

Figure 10-2 shows a switched network without VTP pruning enabled. Interface 1 on Switch 1 and Interface 2 on Switch 4 are assigned to the Red VLAN. A broadcast is sent from the host connected to Switch 1. Switch 1 floods the broadcast and every network device in the network receives it, even though Switches 3, 5, and 6 have no interfaces in the Red VLAN.

You can enable pruning globally on the Catalyst 4500 series switch (see the "Enabling VTP Pruning" section).

Figure 10-2 Flooding Traffic without VTP Pruning

Figure 10-3 shows the same switched network with VTP pruning enabled. The broadcast traffic from Switch 1 is not forwarded to Switches 3, 5, and 6 because traffic for the Red VLAN has been pruned on the links indicated (Interface 5 on Switch 2 and Interface 4 on Switch 4).

Figure 10-3 Flooding Traffic with VTP Pruning

Enabling VTP pruning on a VTP server enables pruning for the entire management domain. VTP pruning takes effect several seconds after you enable it. By default, VLANs 2 through 1000 are eligible for pruning. VTP pruning does not prune traffic from pruning-ineligible VLANs. VLAN 1 is always ineligible for pruning; traffic from VLAN 1 cannot be pruned.

To configure VTP pruning on a trunking LAN interface, use the switchport trunk pruning vlan command. VTP pruning operates when a LAN interface is trunking. You can set VLAN pruning eligibility regardless of whether VTP pruning is enabled or disabled for the VTP domain, whether any given VLAN exists, and regardless of whether the LAN interface is currently trunking.

VTP Configuration Guidelines and Restrictions

Follow these guidelines and restrictions when implementing VTP in your network:

•All network devices in a VTP domain must run the same VTP version.

•You must configure a password on each network device in the management domain when VTP is in secure mode.

Caution If you configure VTP in secure mode, the management domain will not function properly if you do not assign a management domain password to each network device in the domain.

•A VTP version 2-capable network device can operate in the same VTP domain as a network device running VTP version 1 if VTP version 2 is disabled on the VTP version 2-capable network device (VTP version 2 is disabled by default).

•Do not enable VTP version 2 on a network device unless all of the network devices in the same VTP domain are version 2-capable. When you enable VTP version 2 on a server, all of the version 2-capable network devices in the domain enable VTP version 2.

•Enabling or disabling VTP pruning on a VTP server enables or disables VTP pruning for the entire management domain.

•Configuring VLANs as eligible for pruning on a Catalyst 4500 series switch affects pruning eligibility for those VLANs on that switch only, not on all network devices in the VTP domain.

VTP Default Configuration

Table 10-3 shows the default VTP configuration.

Configuring VTP

The following sections describe how to configure VTP:

•Configuring VTP Global Parameters

•Configuring the Switch as a VTP Server

•Configuring the Switch as a VTP Client

•Disabling VTP (VTP Transparent Mode)

•Displaying VTP Statistics

Configuring VTP Global Parameters

The following sections describe configuring the VTP global parameters:

•Configuring a VTP Password

•Enabling VTP Pruning

•Enabling VTP Version 2

Configuring a VTP Password

To configure the VTP password, perform this task:

Switch# [no] vtp password 
password_string 

This example shows how to configure a VTP password:

Switch# vtp password WATER

Setting device VLAN database password to WATER.

Switch#show vtp password

VTP Password:WATER

Switch#

Enabling VTP Pruning

To enable VTP pruning in the management domain, perform this task:

Switch# [no] vtp pruning 

Switch# show vtp status 

This example shows how to enable VTP pruning in the management domain:

Switch# vtp pruning

Pruning switched ON

This example shows how to verify the configuration:

Switch# show vtp status | include Pruning

VTP Pruning Mode                : Enabled

Switch# 

Enabling VTP Version 2

By default, VTP version 2 is disabled on VTP version 2-capable network devices. When you enable VTP
version 2 on a server, every VTP version 2-capable network device in the VTP domain enables version 2.

Caution VTP version 1 and VTP version 2 are not interoperable on network devices in the same VTP domain. Every network device in the VTP domain must use the same VTP version. Do not enable VTP version 2 unless every network device in the VTP domain supports version 2.

To enable VTP version 2, perform this task:

Switch# [no] vtp version {1 | 2} 

Switch# show vtp status 

This example shows how to enable VTP version 2:

Switch# vtp version 2

V2 mode enabled.

Switch# 

This example shows how to verify the configuration:

Switch# show vtp status | include V2

VTP V2 Mode                     : Enabled

Switch# 

Configuring the Switch as a VTP Server

To configure the Catalyst 4500 series switch as a VTP server, perform this task:

Switch# configuration terminal

Switch(config)# vtp mode server 

Switch(config)# vtp domain domain_name 

Switch(config)# end 

Switch# show vtp status 

This example shows how to configure the switch as a VTP server:

Switch# configuration terminal

Switch(config)# vtp mode server

Setting device to VTP SERVER mode.

Switch(config)# vtp domain Lab_Network

Setting VTP domain name to Lab_Network

Switch(config)# end

Switch# 

This example shows how to verify the configuration:

Switch# show vtp status 

VTP Version                     : 2

Configuration Revision          : 247

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 33

VTP Operating Mode              : Server

VTP Domain Name                 : Lab_Network

VTP Pruning Mode                : Enabled

VTP V2 Mode                     : Disabled

VTP Traps Generation            : Disabled

MD5 digest                      : 0x45 0x52 0xB6 0xFD 0x63 0xC8 0x49 0x80

Configuration last modified by 0.0.0.0 at 8-12-99 15:04:49

Local updater ID is 172.20.52.34 on interface Gi1/1 (first interface found) 

Switch# 

Configuring the Switch as a VTP Client

To configure the Catalyst 4500 series switch as a VTP client, perform this task:

Switch# configuration terminal 

Switch(config)# [no] vtp mode client

Switch(config)# end 

Switch# show vtp status 

This example shows how to configure the switch as a VTP client:

Switch# configuration terminal

Switch(config)# vtp mode client

Setting device to VTP CLIENT mode.

Switch(config)# exit

Switch# 

This example shows how to verify the configuration:

Switch# show vtp status 

VTP Version                     : 2

Configuration Revision          : 247

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 33

VTP Operating Mode              : Client

VTP Domain Name                 : Lab_Network

VTP Pruning Mode                : Enabled

VTP V2 Mode                     : Disabled

VTP Traps Generation            : Disabled

MD5 digest                      : 0x45 0x52 0xB6 0xFD 0x63 0xC8 0x49 0x80

Configuration last modified by 0.0.0.0 at 8-12-99 15:04:49

Switch# 

Disabling VTP (VTP Transparent Mode)

To disable VTP on the Catalyst 4500 series switch, perform this task:

Switch# configuration terminal 

Switch(config)# [no] vtp mode transparent

Switch(config)# end 

Switch# show vtp status 

This example shows how to disable VTP on the switch:

Switch# configuration terminal

Switch(config)# vtp transparent

Setting device to VTP mode.

Switch(config)# end

Switch# 

This example shows how to verify the configuration:

Switch# show vtp status 

VTP Version                     : 2

Configuration Revision          : 247

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 33

VTP Operating Mode              : Transparent

VTP Domain Name                 : Lab_Network

VTP Pruning Mode                : Enabled

VTP V2 Mode                     : Disabled

VTP Traps Generation            : Disabled

MD5 digest                      : 0x45 0x52 0xB6 0xFD 0x63 0xC8 0x49 0x80

Configuration last modified by 0.0.0.0 at 8-12-99 15:04:49

Switch# 

Displaying VTP Statistics

To display VTP statistics, including VTP advertisements sent and received and VTP errors, perform this task:

Switch# show vtp counters 

This example shows how to display VTP statistics:

Switch# show vtp counters

VTP statistics:

Summary advertisements received    : 7

Subset advertisements received     : 5

Request advertisements received    : 0

Summary advertisements transmitted : 997

Subset advertisements transmitted  : 13

Request advertisements transmitted : 3

Number of config revision errors   : 0

Number of config digest errors     : 0

Number of V1 summary errors        : 0

VTP pruning statistics:

Trunk            Join Transmitted Join Received    Summary advts received from

                                                   non-pruning-capable device

---------------- ---------------- ---------------- ---------------------------

Fa5/8               43071            42766            5

VLAN Membership Policy Server

This section describes how to configure dynamic port VLAN membership through the VLAN Membership Policy Server (VMPS).

This section includes the following subsections:

•Overview of VMPS

•Overview of VMPS Clients

•Dynamic Port VLAN Membership Configuration Example

•VMPS Database Configuration File Example

Overview of VMPS

These subsections describe what a VMPS server does and how it operates:

•Understanding the VMPS Server

•Security Modes for VMPS Server

•Fall-back VLAN

•Illegal VMPS client requests

Understanding the VMPS Server

A VLAN Membership Policy Server (VMPS) provides a centralized server for selecting the VLAN for a port dynamically based on the MAC address of the device connected to the port. When the host moves from a port on one switch in the network to a port on another switch in the network, that switch dynamically assigns the new port to the proper VLAN for that host.

A Catalyst 4500 series switch running Cisco IOS software does not support the functionality of a VMPS. It can only function as a VLAN Query Protocol (VQP) client, which communicates with a VMPS through the VQP. For VMPS functionality, you need to use a Catalyst 4500 series switch (or Catalyst 6500 series switch) running Catalyst operating system (OS) software.

VMPS uses a UDP port to listen to VQP requests from clients, so, it is not necessary for VMPS clients to know if the VMPS resides on a local or remote device on the network. Upon receiving a valid request from a VMPS client, a VMPS server searches its database for an entry of a MAC-address to VLAN mapping.

In response to a request, the VMPS takes one of the following actions:

•If the assigned VLAN is restricted to a group of ports, the VMPS verifies the requesting port against this group and responds as follows:

–If the VLAN is allowed on the port, the VMPS sends the VLAN name to the client in response.

–If the VLAN is not allowed on the port and the VMPS is not in secure mode, the VMPS sends an "access-denied" response.

–If the VLAN is not allowed on the port and the VMPS is in secure mode, the VMPS sends a "port-shutdown" response.

•If the VLAN in the database does not match the current VLAN on the port and there are active hosts on the port, the VMPS sends an "access-denied" (open), a "fallback VLAN name" (open with fallback VLAN configured), a "port-shutdown" (secure), or a "new VLAN name" (multiple) response, depending on the secure mode setting of the VMPS.

If the switch receives an "access-denied" response from the VMPS, the switch continues to block traffic from the MAC address to or from the port. The switch continues to monitor the packets directed to the port and sends a query to the VMPS when it identifies a new address. If the switch receives a "port-shutdown" response from the VMPS, the switch disables the port. The port must be manually re-enabled by using the CLI, Cisco Visual Switch Manager (CVSM), or SNMP.

You can also use an explicit entry in the configuration table to deny access to specific MAC addresses for security reasons. If you enter the none keyword for the VLAN name, the VMPS sends an "access-denied" or "port-shutdown" response.

For more information on a Catalyst 6500 series switch VMPS running Catalyst operating system software, refer to the
"Configuring Dynamic Port VLAN Membership with VMPS" chapter at the URL:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_8_3/confg_gd/vmps.htm

Security Modes for VMPS Server

VMPS operates in three different modes. The way a VMPS server responds to illegal requests depends on the mode in which the VMPS is configured:

•Open mode

•Secure mode

•Multiple mode

Open mode

If no VLAN has been assigned to this port, VMPS verifies the requesting MAC address against this port:

•If the VLAN associated with this MAC address is allowed on the port, the VLAN name is returned to the client.

•If the VLAN associated with this MAC address is not allowed on the port, the host receives an "access denied" response.

If a VLAN is already assigned to this port, VMPS verifies the requesting MAC address against this port:

•If the VLAN associated with this MAC address in the database does not match the current VLAN assigned on the port and a fallback VLAN name is configured, VMPS sends the fallback VLAN name to the client.

•If a VLAN associated with this MAC address in the database does not match the current VLAN assigned on the port and a fallback VLAN name is not configured, the host receives an "access denied" response.

Secure mode

If no VLAN has been assigned to this port, VMPS verifies the requesting MAC address against this port:

•If the VLAN associated with this MAC address is allowed on the port, the VLAN name is returned to the client.

•If the VLAN associated with this MAC address is not allowed on the port, the port is shut down.

If a VLAN is already assigned to this port, VMPS verifies the requesting MAC address against this port:

•If a VLAN associated with this MAC address in the database does not match the current VLAN assigned on the port, the port is shutdown, even if a fallback VLAN name is configured.

Multiple mode

Multiple hosts (MAC addresses) can be active on a dynamic port if they are all in the same VLAN. If the link goes down on a dynamic port, the port returns to the unassigned state. Any hosts that come online through the port are checked again with VMPS before the port is assigned to a VLAN.

If multiple hosts connected to a dynamic port belong to different VLANs, the VLAN matching the MAC address in the last request is returned to the client, provided that multiple mode is configured on the VMPS server.

Note Although Catalyst 4500 series and Catalyst 6500 series switches running Catalyst operating system software support VMPS in all three operation modes, the Cisco network management tool URT (User Registration Tool) supports open mode only.

Fall-back VLAN

You can configure a fallback VLAN name on a VMPS server.

If no VLAN has been assigned to this port, VMPS verifies the requesting MAC address against this port:

•If you connect a device with a MAC address that is not in the database, the VMPS sends the fallback VLAN name to the client.

•If you do not configure a fallback VLAN name and the MAC address does not exist in the database, the VMPS sends an "access-denied" response.

If a VLAN is already assigned to this port, VMPS verifies the requesting MAC address against this port

•If the VMPS is in secure mode, it sends a "port-shutdown" response, whether or not a fallback VLAN has been configured on the server.

Illegal VMPS client requests

Two examples of illegal VMPS client requests are as follows:

•When a MAC-address mapping is not present in the VMPS database and "no fall back" VLAN is configured on the VMPS.

•When a port is already assigned a VLAN (and the VMPS mode is not "multiple") but a second VMPS client request is received on the VMPS for a different MAC-address.

Overview of VMPS Clients

The following subsections describe how to configure a switch as a VMPS client and configure its ports for dynamic VLAN membership.

The following topics are included:

•Understanding Dynamic VLAN Membership

•Default VMPS Client Configuration

•Configuring a Switch as a VMPS Client

•Administering and Monitoring the VMPS

•Troubleshooting Dynamic Port VLAN Membership

Understanding Dynamic VLAN Membership

When a port is configured as "dynamic," it receives VLAN information based on the MAC-address that is on the port. The VLAN is not statically assigned to the port; it is dynamically acquired from the VMPS based on the MAC-address on the port.

A dynamic port can belong to one VLAN only. When the link becomes active, the switch does not forward traffic to or from this port until the port is assigned to a VLAN. The source MAC address from the first packet of a new host on the dynamic port is sent to the VMPS as part of the VQP request, which attempts to match the MAC address to a VLAN in the VMPS database. If there is a match, the VMPS sends the VLAN number for that port. If there is no match, the VMPS either denies the request or shuts down the port (depending on the VMPS security mode setting). See the "Overview of VMPS" section for a complete description of possible VMPS responses.

Multiple hosts (MAC addresses) can be active on a dynamic port if all are in the same VLAN. If the link goes down on a dynamic port, the port returns to the unassigned state and does not belong to a VLAN. Any hosts that come online through the port are checked again with the VMPS before the port is assigned to a VLAN.

For this behavior to work, the client device must be able to reach the VMPS. A VMPS client sends VQP requests as UDP packets, trying a certain number of times before giving up. For details on how to set the retry interval, refer to section "Configuring the Retry Interval" on page 25.

The VMPS client also periodically reconfirms the VLAN membership. For details on how to set the reconfirm frequency, refer to section "Administering and Monitoring the VMPS" on page 25.

A maximum of 50 hosts are supported on a given port at any given time. Once this maximum is exceeded, the port is shut down, irrespective of the operating mode of the VMPS server.

Note The VMPS shuts down a dynamic port if more than 50 hosts are active on that port.

Default VMPS Client Configuration

Table 10-4 shows the default VMPS and dynamic port configuration on client switches.

Configuring a Switch as a VMPS Client

This section contains the following topics:

•Configuring the IP Address of the VMPS Server

•Configuring Dynamic Access Ports on a VMPS Client

•Reconfirming VLAN Memberships

•Configuring Reconfirmation Interval

•Reconfirming VLAN Memberships

Configuring the IP Address of the VMPS Server

To configure a Catalyst 4500 series switch as a VMPS client, you must enter the IP address or hostname of the switch acting as the VMPS.

To define the primary and secondary VMPS on a Catalyst 4500 series switch, perform this task:

Switch# configure terminal

Switch(config)# vmps server  
{ipaddress | hostname} primary

Switch(config)# vmps server  
{ipaddress | hostname}

Switch(config)# end

Switch# show vmps

This example shows how to define the primary and secondary VMPS devices:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# vmps server 172.20.128.179 primary

Switch(config)# vmps server 172.20.128.178

Switch(config)# end

Note You can configure up to four VMPS servers using this CLI on the VMPS client.

Switch# show vmps

VQP Client Status:

--------------------

VMPS VQP Version:   1

Reconfirm Interval: 60 min

Server Retry Count: 3

VMPS domain server: 172.20.128.179 (primary, current)

                    172.20.128.178

Reconfirmation status

---------------------

VMPS Action:         No Dynamic Port

Configuring Dynamic Access Ports on a VMPS Client

To configure a dynamic access port on a VMPS client switch, perform this task:

Switch# configure terminal

Switch(config)# interface interface

Switch(config-if)# switchport mode 
access

Switch(config-if)# switchport access 
vlan dynamic

Switch(config-if)# end

Switch# show interface interface 
switchport

This example shows how to configure a dynamic access port and to verify the entry:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# interface fa1/1

Switch(config-if)# switchport mode access

Switch(config-if)# switchport access vlan dynamic

Switch(config-if)# end

Switch# show interface fa1/1 switchport

Name: Fa0/1

Switchport: Enabled

Administrative mode: dynamic auto

Operational Mode: dynamic access

Administrative Trunking Encapsulation: isl

Operational Trunking Encapsulation: isl

Negotiation of Trunking: Disabled

Access Mode VLAN: 0 ((Inactive))

Trunking Native Mode VLAN: 1 (default)

Trunking VLANs Enabled: NONE

Pruning VLANs Enabled: NONE 

Voice Ports

If a VVID (voice VLAN ID) is configured on a dynamic access port, the port can belong to both an access VLAN and a voice VLAN. Consequently, an access port configured for connecting an IP phone can have separate VLANs for the following:

•Data traffic to and from the PC that is connected to the switch through the access port of the IP phone (access VLAN)

•Voice traffic to and from the IP phone (voice VLAN)

Reconfirming VLAN Memberships

To confirm the dynamic port VLAN membership assignments that the switch has received from the VMPS, perform this task:

Switch# vmps reconfirm 

Switch# show vmps

Configuring Reconfirmation Interval

VMPS clients periodically reconfirm the VLAN membership information received from the VMPS. You can set the number of minutes the VMPS client waits before reconfirming the VLAN-to-MAC-address assignments.

To configure the reconfirmation interval, perform this task:

Switch# configure terminal

Switch(config)# vmps reconfirm minutes

Switch(config)# end

Switch# show vmps

This example shows how to change the reconfirmation interval to 60 minutes and verify the change:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# vmps reconfirm 60

Switch(config)# end

Switch# show vmps

VQP Client Status:

--------------------

VMPS VQP Version:   1

Reconfirm Interval: 60 min

Server Retry Count: 10

VMPS domain server: 172.20.130.50 (primary, current)

Reconfirmation status

---------------------

VMPS Action:         No Host 

Configuring the Retry Interval

You can set the number of times that the VMPS client attempts to contact the VMPS before querying the next server.

To configure the retry interval, perform this task:

Switch# configure terminal

Switch(config)# vmps retry count

Switch(config)# end

Switch# show vmps

This example shows how to change the retry count to 5 and to verify the change:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# vmps retry 5

Switch(config)# end

Switch# show vmps

VQP Client Status:

--------------------

VMPS VQP Version:   1

Reconfirm Interval: 60 min

Server Retry Count: 5

VMPS domain server: 172.20.130.50 (primary, current)

Reconfirmation status

---------------------

VMPS Action:         No Host 

Administering and Monitoring the VMPS

You can display the following information about the VMPS with the show vmps command:

The following example shows how to display VMPS information:

Switch# show vmps

VQP Client Status:

--------------------

VMPS VQP Version:   1

Reconfirm Interval: 60 min

Server Retry Count: 3

VMPS domain server:

Reconfirmation status

---------------------

VMPS Action:         other

The following example shows how to display VMPS statistics:

Switch# show vmps statistics

VMPS Client Statistics

----------------------

VQP  Queries:               0

VQP  Responses:             0

VMPS Changes:               0

VQP  Shutdowns:             0

VQP  Denied:                0

VQP  Wrong Domain:          0

VQP  Wrong Version:         0

VQP  Insufficient Resource: 0

Note Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference for details on VMPS statistics.

Troubleshooting Dynamic Port VLAN Membership

VMPS errdisables a dynamic port under the following conditions:

•The VMPS is in secure mode, and it will not allow the host to connect to the port. The VMPS errdisables the port to prevent the host from connecting to the network.

•More than 50 active hosts reside on a dynamic port.

For information on how to display the status of interfaces in error-disabled state, refer to
Chapter 5, "Checking Port Status and Connectivity." To recover an errdisabled port, use the
errdisable recovery cause vmps global configuration command.

Dynamic Port VLAN Membership Configuration Example

Figure 10-4 shows a network with a VMPS servers and VMPS client switches with dynamic ports. In this example, these assumptions apply:

•The VMPS server and the VMPS client are separate switches.

•The Catalyst 4000 family Switch 1 (running CatOS) is the primary VMPS server.

•The Catalyst 6000 family Switch 3 (running CatOS) and the URT are secondary VMPS servers.

•End stations are connected to these clients:

–Catalyst 4500 series XL Switch 2 (running Catalyst IOS)

–Catalyst 4500 series XL Switch 9 (running Catalyst IOS)

•The database configuration file is called Bldg-G.db and is stored on the TFTP server with the IP address 172.20.22.7.

Figure 10-4 Dynamic Port VLAN Membership Configuration - VMPS Servers and Clients

Two topologies are possible. Figure 10-5 illustrates a topology with one end station attached directly to a Catalyst 4500 series switch operating as a VMPS client. Figure 10-6 illustrates a topology with an end station attached to a Cisco IP Phone, which is attached to a Catalyst 4500 series switch.

Figure 10-5 Dynamic Port VLAN Membership Configuration - Station Attached to Switch

Figure 10-6 Dynamic Port VLAN Membership Configuration - Station Attached to Phone

In the following procedure, the Catalyst 4000 and Catalyst 6000 series switches (running CatOS) are the VMPS servers. Use this procedure to configure the Catalyst 4500 series switch clients in the network:

Step 1 Configure the VMPS server addresses on Switch 2, the client switch.

a. Starting from privileged EXEC mode, enter global configuration mode:

switch# configuration terminal

b. Enter the primary VMPS server IP address:

switch(config)# vmps server 172.20.26.150 primary

c. Enter the secondary VMPS server IP addresses:

switch(config)# vmps server 172.20.26.152

d. To verify your entry of the VMPS IP addresses, return to privileged EXEC mode:

switch#(config) exit

e. Display VMPS information configured for the switch:

switch# show vmps

VQP Client Status:

--------------------

VMPS VQP Version:   1

Reconfirm Interval: 60 min

Server Retry Count: 3

VMPS domain server: 172.20.26.152

                    172.20.26.150 (primary, current

Step 2 Configure port Fa0/1 on Switch 2 as a dynamic port.

a. Return to global configuration mode:

switch# configure terminal

b. Enter interface configuration mode:

switch(config)# interface fa2/1

c. Configure the VLAN membership mode for static-access ports:

switch(config-if)# switchport mode access

d. Assign the port dynamic VLAN membership:

switch(config-if)# switchport access vlan dynamic

e. Return to privileged EXEC mode:

switch(config-if)# exit

switch#

Step 3 Connect End Station 2 on port Fa2/1. When End Station 2 sends a packet, Switch 2 sends a query to the primary VMPS server, Switch 1. Switch 1 responds with the VLAN ID for port Fa2/1. If spanning-tree PortFast mode is enabled on Fa2/1, port Fa2/1 connects immediately and begins forwarding.

Step 4 Set the VMPS reconfirmation period to 60 minutes. The reconfirmation period is the number of minutes the switch waits before reconfirming the VLAN to MAC address assignments.

switch# config terminal

switch(config)# vmps reconfirm 60

Step 5 Confirm the entry from privileged EXEC mode:

switch# show vmps

VQP Client Status:

--------------------

VMPS VQP Version:   1

Reconfirm Interval: 60 min

Server Retry Count: 3

VMPS domain server:

Reconfirmation status

---------------------

VMPS Action:         No Dynamic Port

Step 6 Repeat Steps 1 and 2 to configure the VMPS server addresses, and assign dynamic ports on each VMPS client switch.

VMPS Database Configuration File Example

This example shows a sample VMPS database configuration file as it appears on a VMPS server. A VMPS database configuration file is an ASCII text file that is stored on a TFTP server accessible to the switch that functions as the VMPS server.

!vmps domain <domain-name>

! The VMPS domain must be defined.

!vmps mode { open | secure }

! The default mode is open.

!vmps fallback <vlan-name>

!vmps no-domain-req { allow | deny }

!

! The default value is allow.

vmps domain WBU

vmps mode open

vmps fallback default

vmps no-domain-req deny

!

!

!MAC Addresses

!

vmps-mac-addrs

!

! address <addr> vlan-name <vlan_name>

!

address 0012.2233.4455 vlan-name hardware

address 0000.6509.a080 vlan-name hardware

address aabb.ccdd.eeff vlan-name Green

address 1223.5678.9abc vlan-name ExecStaff

address fedc.ba98.7654 vlan-name --NONE--

address fedc.ba23.1245 vlan-name Purple

!

!Port Groups

!

!vmps-port-group <group-name>

! device <device-id> { port <port-name> | all-ports }

!

vmps-port-group WiringCloset1

 device 198.92.30.32 port Fa1/3

 device 172.20.26.141 port Fa1/4

vmps-port-group "Executive Row"

 device 198.4.254.222 port es5%Fa0/1

 device 198.4.254.222 port es5%Fa0/2

 device 198.4.254.223 all-ports

!

!VLAN groups

!

!vmps-vlan-group <group-name>

! vlan-name <vlan-name>

!

vmps-vlan-group Engineering

vlan-name hardware

vlan-name software

!

!VLAN port Policies

!

!vmps-port-policies {vlan-name <vlan_name> | vlan-group <group-name> }

! { port-group <group-name> | device <device-id> port <port-name> }

!

vmps-port-policies vlan-group Engineering

 port-group WiringCloset1

vmps-port-policies vlan-name Green

 device 198.92.30.32 port Fa0/9

vmps-port-policies vlan-name Purple

 device 198.4.254.22 port Fa0/10

 port-group "Executive Row"