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This chapter describes how to configure the VLAN Trunk Protocol (VTP) on the Catalyst 6000 family switches.
This chapter consists of these sections:
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 switches 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 switches and have those changes automatically communicated to all the other switches in the network.
These sections describe how VTP works:
A VTP domain (also called a VLAN management domain) is made up of one or more interconnected switches that share the same VTP domain name. A switch 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 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. 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 switches in the VTP domain. VTP advertisements are transmitted out all trunk connections, including Inter-Switch Link (ISL), IEEE 802.1Q, IEEE 802.10, and ATM LAN Emulation (LANE).
VTP maps VLANs dynamically across multiple LAN types with unique names and internal index associations. Mapping eliminates excessive device administration required from network administrators.
You can configure a switch to operate in any one of these VTP modes:
Each switch in the VTP domain sends periodic advertisements out each trunk interface to a reserved multicast address. VTP advertisements are received by neighboring switches, which update their VTP and VLAN configurations as necessary.
The following global configuration information is distributed in VTP advertisements:
If you use VTP in your network, you must decide whether to use VTP version 1 or version 2.
VTP version 2 supports the following features not supported in version 1:
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 either support VTP pruning or, on devices that do not support VTP pruning, you must manually configure the VLANs allowed on trunks.
Figure 7-1 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 switch in the network receives it, even though Switches 3, 5, and 6 have no interfaces in the Red VLAN.
You enable pruning globally on the switch (see the "Enabling VTP Pruning" section). You configure pruning on Layer 2 trunk interfaces (see the "Configuring an Ethernet Interface as a Layer 2 Trunk" section).
Figure 7-2 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 (interface 5 on Switch 2 and interface 4 on Switch 4).
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 VLANs that are pruning-ineligible. VLAN 1 is always pruning-ineligible; traffic from VLAN 1 cannot be pruned.
To configure VTP pruning on an interface, use the switchport trunk pruning vlan command (see the "Configuring an Ethernet Interface as a Layer 2 Trunk" section). VTP pruning operates when an 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 or not, and regardless of whether the interface is currently trunking or not.
Table 7-1 shows the default VTP configuration.
| Feature | Default Value |
|---|---|
VTP domain name | Null |
VTP mode | Server |
VTP version 2 enable state | Version 2 is disabled |
VTP password | None |
VTP pruning | Disabled |
Follow these guidelines when implementing VTP in your network:
| 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 switch in the domain. |
These sections describe how to configure VTP:
When a switch is in VTP server mode, you can change the VLAN configuration and have it propagate throughout the network.
To configure the switch as a VTP server, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router# vlan database | Enter VLAN configuration mode. | ||
| Router(vlan)# vtp server | Place the switch in VTP server mode. | ||
| Router(vlan)# vtp domain domain_name | Define the VTP domain name, which can be up to 32 characters long. | ||
| Router(vlan)# vtp password password_value | (Optional) Set a password, which can be from 8 to 64 characters long, for the VTP domain. | ||
| Router(vlan)# exit | Exit the VLAN configuration mode. | ||
| Router# show vtp status | Display VTP status. |
This example shows how to configure the switch as a VTP server:
Router# vlan database Router(vlan)# vtp server Setting device to VTP SERVER mode. Router(vlan)# vtp domain Lab_Network Setting VTP domain name to Lab_Network Router(vlan)# vtp password WATER Setting device VLAN database password to WATER. Router(vlan)# exit APPLY completed. Exiting.... 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#
When a switch is in VTP client mode, you cannot change the VLAN configuration on the switch. The client switch receives VTP updates from a VTP server in the management domain and modifies its configuration accordingly.
To configure the switch as a VTP client, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router# vlan database | Enter VLAN configuration mode. | ||
| Router(vlan)# vtp client | Place the switch in VTP client mode. | ||
| Router(vlan)# exit | Exit the VLAN configuration mode. | ||
| Router# show vtp status | Display VTP status. |
This example shows how to configure the switch as a VTP client:
Router# vlan database Router(vlan)# vtp client Setting device to VTP CLIENT mode. Router(vlan)# exit In CLIENT state, no apply attempted. Exiting.... 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#
When you configure the switch as VTP transparent, you disable VTP on the switch. A VTP transparent switch does not send VTP updates and does not act on VTP updates received from other switches. However, a VTP transparent switch running VTP version 2 does forward received VTP advertisements out all of its trunk links.
To disable VTP on the switch, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router# vlan database | Enter VLAN configuration mode. | ||
| Router(vlan)# vtp transparent | Place the switch in VTP transparent mode. | ||
| Router(vlan)# exit | Exit the VLAN configuration mode. | ||
| Router# show vtp status | Display VTP status. |
This example shows how to configure the switch as VTP transparent:
Router# vlan database Router(vlan)# vtp transparent Setting device to VTP TRANSPARENT mode. Router(vlan)# exit APPLY completed. Exiting.... 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#
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 will enable version 2 as well.
| Caution 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. |
To enable VTP version 2, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router# vlan database | Enter VLAN configuration mode. | ||
| Router(vlan)# vtp v2-mode | Enable VTP version 2. | ||
| Router(vlan)# exit | Exit the VLAN configuration mode. | ||
| Router# show vtp status | Display VTP status. |
This example shows how to enable VTP version 2:
Router# vlan database Router(vlan)# vtp v2-mode V2 mode enabled. Router(vlan)# exit APPLY completed. Exiting.... 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 : Enabled 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#
To disable VTP version 2, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router# vlan database | Enter VLAN configuration mode. | ||
| Router(vlan)# no vtp v2-mode | Disable VTP version 2. | ||
| Router(vlan)# exit | Exit the VLAN configuration mode. | ||
| Router# show vtp status | Display VTP status. |
This example shows how to enable VTP version 2:
Router# vlan database Router(vlan)# no vtp v2-mode V2 mode disabled. Router(vlan)# exit APPLY completed. Exiting.... 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#
To enable VTP pruning, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router# vlan database | Enter VLAN configuration mode. | ||
| Router(vlan)# vtp pruning | Enable VTP pruning in the management domain. | ||
| Router(vlan)# exit | Exit the VLAN configuration mode. | ||
| Router# show vtp status | Display VTP status. |
This example shows how to enable VTP pruning in the management domain:
Router# vlan database Router(vlan)# vtp pruning Pruning switched ON Router(vlan)# exit APPLY completed. Exiting.... Router# show vtp status VTP Version : 2 Configuration Revision : 250 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 : Enabled VTP Traps Generation : Disabled MD5 digest : 0xE6 0xF8 0x3E 0xDD 0xA4 0xF5 0xC2 0x0E Configuration last modified by 172.20.52.18 at 9-22-99 11:18:20 Local updater ID is 172.20.52.18 on interface Vl1 (lowest numbered VLAN interfac e found) Router#
To disable VTP pruning, perform this task:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router# vlan database | Enter VLAN configuration mode. | ||
| Router(vlan)# no vtp pruning | Enable VTP pruning in the management domain. | ||
| Router(vlan)# exit | Exit the VLAN configuration mode. | ||
| Router# show vtp status | Display VTP status. |
This example shows how to disable VTP pruning in the management domain:
Router# vlan database Router(vlan)# no vtp pruning Pruning switched OFF Router(vlan)# exit APPLY completed. Exiting.... Router# show vtp status VTP Version : 2 Configuration Revision : 249 Maximum VLANs supported locally : 1005 Number of existing VLANs : 33 VTP Operating Mode : Server VTP Domain Name : Lab_Network VTP Pruning Mode : Disabled VTP V2 Mode : Enabled VTP Traps Generation : Disabled MD5 digest : 0x08 0x66 0x9D 0x64 0xAB 0x95 0xA8 0x0F Configuration last modified by 172.20.52.18 at 9-22-99 11:14:34 Local updater ID is 172.20.52.18 on interface Vl1 (lowest numbered VLAN interfac e found) Router#
To monitor VTP activity, including VTP advertisements sent and received and VTP errors, perform this task:
| Command | Purpose |
|---|---|
Router# show vtp counters | Display VTP statistics for the switch. |
This example shows how to display VTP statistics on the switch:
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
Posted: Mon Jan 3 14:31:23 PST 2000
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