Catalyst Supervisor Engine 32 PISA IOS Software Configuration Guide, 12.2ZY

Configuring VTP

This chapter describes how to configure the VLAN Trunking Protocol (VTP) on the Catalyst 6500 series switches.

Note For complete syntax and usage information for the commands used in this chapter, refer to the Catalyst Supervisor Engine 32 PISA Cisco IOS Command Reference, Release 12.2ZY, at this URL:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2ZY/command/reference/cmdref.html

This chapter consists of these sections:

•Understanding How VTP Works

•VTP Default Configuration

•VTP Configuration Guidelines and Restrictions

•Configuring VTP

Understanding How VTP Works

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 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.

Note For complete information on configuring VLANs, see Chapter 12 "Configuring 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 (also called a VLAN management 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 one and 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 6500 series switch is in VTP server 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.

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 trunk connections.

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

Understanding VTP Modes

You can configure a Catalyst 6500 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 out their trunking LAN ports.

Note Catalyst 6500 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 port 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 If you are using VTP in a Token Ring environment, you must use version 2.

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

•Token Ring support—VTP version 2 supports Token Ring LAN switching and VLANs (Token Ring Bridge Relay Function [TrBRF] and Token Ring Concentrator Relay Function [TrCRF]). For more information about Token Ring VLANs, see the "Understanding How VLANs Work" section.

•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, unknown, and flooded 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 support VTP pruning. On devices that do not support VTP pruning, you must manually configure the VLANs allowed on trunks.

Figure 11-1 shows a switched network without VTP pruning enabled. Interface 1 on network Switch 1 and port 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 ports in the Red VLAN.

You enable pruning globally on the Catalyst 6500 series switch (see the "Enabling VTP Pruning" section). You configure pruning on Layer 2 trunking LAN ports (see the "Configuring a Layer 2 Switching Port as a Trunk" section).

Figure 11-1 Flooding Traffic without VTP Pruning

Figure 11-2 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 (port 5 on Switch 2 and port 4 on Switch 4).

Figure 11-2 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 pruning eligible. VTP pruning does not prune traffic from pruning-ineligible VLANs. VLAN 1 is always pruning ineligible; traffic from VLAN 1 cannot be pruned.

To configure VTP pruning on a trunking LAN port, use the switchport trunk pruning vlan command (see the "Configuring a Layer 2 Switching Port as a Trunk" section). VTP pruning operates when a LAN port is trunking. You can set VLAN pruning eligibility when VTP pruning is enabled or disabled for the VTP domain, when any given VLAN exists or not, and when the LAN port is currently trunking or not.

VTP Default Configuration

Table 11-1 shows the default VTP configuration.

VTP Configuration Guidelines and Restrictions

When implementing VTP in your network, follow these guidelines and 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.

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

•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 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 provided 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 network device, all of the version 2-capable network devices in the domain enable VTP version 2.

•In a Token Ring environment, you must enable VTP version 2 for Token Ring VLAN switching to function properly.

•When you enable or disable VTP pruning on a VTP server, VTP pruning for the entire management domain is enabled or disabled.

•The pruning-eligibility configuration applies globally to all trunks on the switch. You cannot configure pruning-eligibility separately for each trunk.

•When you configure VLANs as pruning eligible or pruning ineligible, pruning eligibility for those VLANs is affected on that switch only, not on all network devices in the VTP domain.

•If there is insufficient DRAM available for use by VTP, the VTP mode changes to transparent.

•Network devices in VTP transparent mode do not send VTP Join messages. On Catalyst 6500 series switches with trunk connections to network devices in VTP transparent mode, configure the VLANs that are used by the transparent-mode network devices or that need to be carried across trunks as pruning ineligible. For information about configuring prune eligibility, see the "Configuring the List of Prune-Eligible VLANs" section.

Configuring VTP

These sections describe how to configure VTP:

•Configuring VTP Global Parameters

•Configuring the VTP Mode

•Displaying VTP Statistics

Configuring VTP Global Parameters

These sections describe configuring the VTP global parameters:

•Configuring a VTP Password

•Enabling VTP Pruning

•Enabling VTP Version 2

Note You can enter the VTP global parameters in either global configuration mode or in EXEC mode.

Configuring a VTP Password

To configure the VTP global parameters, perform this task:

This example shows one way to configure a VTP password in global configuration mode:

Router# configure terminal 

Router(config)# vtp password WATER 

Setting device VLAN database password to WATER.

Router# 

This example shows how to configure a VTP password in EXEC mode:

Router# vtp password WATER

Setting device VLAN database password to WATER.

Router# 

Note The password is not stored in the running-config file.

Enabling VTP Pruning

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

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

Router# configure terminal 

Router(config)# vtp pruning

Pruning switched ON

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

Router# vtp pruning

Pruning switched ON

This example shows how to verify the configuration:

Router# show vtp status | include Pruning

VTP Pruning Mode: Enabled

Router# 

For information about configuring prune eligibility, see the "Configuring the List of Prune-Eligible VLANs" section.

Enabling VTP Version 2

VTP version 2 is disabled by default on VTP version 2-capable network devices. When you enable VTP
version 2 on a network device, 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.

Note In a Token Ring environment, you must enable VTP version 2 for Token Ring VLAN switching to function properly on devices that support Token Ring interfaces.

To enable VTP version 2, perform this task:

This example shows one way to enable VTP version 2:

Router# configure terminal 

Router(config)# vtp version 2 

V2 mode enabled.

Router(config)# 

This example shows how to enable VTP version 2 with any release:

Router# vtp version 2 

V2 mode enabled.

Router# 

This example shows how to verify the configuration:

Router# show vtp status | include V2 

VTP V2 Mode: Enabled

Router# 

Configuring the VTP Mode

To configure the VTP mode, perform this task:

Note When VTP is disabled, you can enter VLAN configuration commands in configuration mode instead of the VLAN database mode and the VLAN configuration is stored in the startup configuration file.

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

Router# configuration terminal

Router(config)# vtp mode server

Setting device to VTP SERVER mode.

Router(config)# vtp domain Lab_Network

Setting VTP domain name to Lab_Network

Router(config)# end

Router# 

This example shows how to verify the configuration:

Router# 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) 

Router# 

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

Router# configuration terminal

Router(config)# vtp mode client

Setting device to VTP CLIENT mode.

Router(config)# exit

Router# 

This example shows how to verify the configuration:

Router# 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

Router# 

This example shows how to disable VTP on the switch:

Router# configuration terminal

Router(config)# vtp mode transparent

Setting device to VTP TRANSPARENT mode.

Router(config)# end

Router# 

This example shows how to verify the configuration:

Router# 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

Router# 

Displaying VTP Statistics

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

This example shows how to display VTP statistics:

Router# 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