VTP Overview

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Client Mode Transparent Mode Client Mode m

Server Mode

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VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs on a network-wide basis. VTP minimizes misconfigurations and configuration inconsistencies that can cause several 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. Using VTP, you can make configuration changes centrally on one or more switches and have those changes automatically communicated to all the other switches in the network. Without VTP, you cannot send information about VLANs to other switches. VTP configuration information is saved in the VTP VLAN database. Catalyst switches can support VTP in one of three modes: Server, Client, and Transparent.

Server: Allows you to 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 switches in the same VTP domain and synchronize their VLAN configuration with other switches based on advertisements received over trunk links. VTP server is the default mode.

■ Client: Behaves the same way as VTP servers, except that you cannot create, change, or delete VLANs on a VTP client.

■ Transparent: Switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. However, in VTP version 2, transparent switches do forward VTP advertisements that they receive out their trunk ports. Transparent mode is required if you want to configure a switch to support extended range VLANs.

On the Catalyst 3550 you can configure VTP in one of two ways: using the vtp global configuration command or using the vtp commands available in VLAN configuration mode.

Note VTP only learns about normal-range VLANs (VLAN IDs 1 to 1005). Extended-range VLANs

(VLAN IDs greater than 1005) are not supported by VTP or stored in the VTP VLAN database.

VTP Configuration using the vtp command

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You can use the vtp global configuration command to set the VTP domain, mode, password, version, VTP file name, and to disable or enable VTP pruning. The information entered with the vtp global configuration command is saved in the VTP VLAN database. When a switch is in VTP server mode, you can change the VLAN configuration and have it propagated throughout the network. In the CCIE lab, you will mostly likely configure at least one of your switches as a VTP Server.

Use the steps outlined in the following table to configure the Catalyst 3550 switch as a VTP server:

Table 4-2: Configure switch as a VTP Server

Command

Purpose

3550(config)# vtp mode server

Configure the switch for VTP server mode (default).

3550(config)# vtp domain domainname

Configure the VTP administrative-domain name. The name can be from 1 to 32 characters. All switches operating in VTP server or client mode under the same administrative responsibility must be configured with the same domain name.

Note When you configure a VTP domain name, it cannot be removed; you can only reassign a switch to a different VTP domain.

VTP Configuration using the vlan database

command

3550# vlan database

3550(vlan)# vtp server

Setting device to VTP SERVER mode. I

3550(vlan)# vtp domain CCIE

Changing VTP domain name from NULL to CCIE

3550(vlan)# vtp password cisco

Setting device VLAN database password to cisco.

3550(vlan)# exit

APPLY completed.

Exiting

3550#

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You can also configure all VTP parameters in VLAN configuration mode, which you access by entering the vlan database command. When you enter the exit command in VLAN configuration mode, it applies all the commands that you entered and updates the VLAN database.

Note Configuring VTP via the vlan database command is the preferred method as some of the advanced settings, such as setting a VTP password, enabling VTP version 2, and enabling VTP pruning, can only be done in the vlan database (vlan) configuration mode.

Use the steps outlined in the following table to use VLAN configuration mode and configure the switch as a VTP server:

Table 4-3: VLAN configuration mode

Command

Purpose

3550# vlan database

Enter VLAN configuration mode.

3550(vlan)# vtp server

Configure a VTP administrative-domain name. The name can be from 1 to 32 characters. All switches operating in VTP server or client mode under the same administrative responsibility must be configured with the same domain name.

3550(vlan)# vtp password password

(Optional) Set a password for the VTP domain. The password can be from 8 to 64 characters. If you configure a VTP password, the VTP domain does not function properly if you do not assign the same password to each switch in the domain.

3550(vlan)# exit

Update the VLAN database, propagate changes throughout the administrative domain, and return to privileged EXEC mode.

Enabling VTP Version 2

ClGl

3550(vlan)# vtp v2-mode

V2 mode enabled. I

3550(vlan)# exit

APPLY completed.

Exiting

3550#

———___

I

— I

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odule 5-10

VTP version 2 is disabled by default on VTP version 2-capable switches. When you enable VTP version 2 on a switch, every VTP version 2-capable switch in the VTP domain enables version 2. You can only configure the version on switches in VTP server or transparent mode.

Note VTP version 1 and VTP version 2 are not interoperable on switches in the same VTP

domain. Every switch in the VTP domain must use the same VTP version. Do not enable VTP version 2 unless every switch in the VTP domain supports version 2.

Use the steps outlined in the following table to enable VTP version 2 on the Catalyst 3550:

Table 4-4: VLAN version 2

Command

Purpose

3550(vlan)# vtp v2-mode

Enable VTP version 2 on the switch. VTP version 2 is disabled by default on VTP version 2-capable switches.

To disable VTP version 2, use the no vtp v2-mode vlan database (vlan) configuration command.

Pruning increases available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to access the destination devices. You can only enable VTP pruning on a switch in VTP server mode. Pruning is supported with VTP version 1 and version 2. If you enable pruning on the VTP server, it is enabled for the entire VTP domain.

Only VLANs included in the pruning-eligible list can be pruned. By default, VLANs 2 through 1001 are pruning eligible on trunk ports. Reserved VLANs and extended-range VLANs cannot be pruned.

Use the steps outlined in the following table to enable VTP pruning in the VTP domain:

Table 4-5: VLAN Pruning

Command

Purpose

3550(vlan)# vtp pruning

Enable pruning in the VTP administrative domain. By default, pruning is disabled. You need to enable pruning on only one switch in VTP server mode.

To disable VTP pruning, use the no vtp pruning vlan database (vlan) configuration command.

Once the switch is properly configured for VTP, you can create, modify, and delete VLANs on the switch (unless you configured the switch as a VTP client). The default Ethernet VLAN is VLAN 1. By default, all switch ports are assigned to VLAN 1. Once VTP is configured, you can create additional VLANs and assign specific switch ports to those VLANs.

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, except that you can group end stations together 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 same VLAN must be forwarded through a router or other Layer 3 engine.

You can configure normal-range VLANs (with VLAN IDs 1 to 1005) by using one of two configuration modes:

■ VLAN Configuration in (config-vlan) Mode

You can access (config-vlan) mode by entering the vlan vlan-id global configuration command.

VLAN Configuration in VLAN Configuration Mode

You can access VLAN configuration mode by entering the vlan database privileged EXEC command.

Configuring VLANs using the vlan command

CiGco.com

3550(config)# vlan

20

3550 (config-vlan)#

name

ENGINEERING

3550 (config-vlan)#

exit

3550 (config)# vlan

30

3550(config-vlan)#

name SALES

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VLAN 20 Engineering

VLAN 30 Sales 172.16.60.0/24

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VLAN 30 Sales 172.16.60.0/24

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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 When the switch is in VTP transparent mode, you can assign VLAN IDs greater than 1006

(Extended Range VLANs), but they are not added to the VLAN database.

Use the steps outlined in the following table to use (config-vlan) mode to create or modify an Ethernet VLAN:

Table 4-6: Ethernet VLAN

Command

Purpose

3550(config)# vlan vlan-id

Enter a new VLAN ID to create a VLAN, or enter an existing VLAN ID to modify a VLAN.

3550(config-vlan)# name vlan-name

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

Configuring VLANs using the vlan database command

3550# vlan database

3550(vlan)# vlan 20 name ENGINEERING

VLAN 2 0 modified:

Name : ENGINEERING

3550(vlan)# vlan 30 name SALES

VLAN 30 modified: Name : SALES 3550(vlan)# exit APPLY completed. Exiting 3550#

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Use the steps outlined in the following table to use VLAN configuration mode to create or modify an Ethernet VLAN:

Table 4-7: Ethernet VLAN

Command

Purpose

3550# vlan database

Enter VLAN configuration mode.

3550(vlan)# vlan vlan-id name vlan-name

Add an Ethernet VLAN by assigning a number to it. The range is 1 to 1001; do not enter leading zeros.

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

3550(vlan)# exit

Updates the VLAN database, propagate changes throughout the VTP administrative domain, and returns to privileged EXEC mode.

This section covers the commands that can be used to troubleshoot VTP and VLAN problems.

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