Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide
Configuring VTP
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Configuring VTP

Configuring VTP

This chapter describes how to configure VLAN Trunking Protocol (VTP) and VTP pruning on Cisco NX-OS devices.

This chapter includes the following sections:

Finding Feature Information

Your software release might not support all the features documented in this module. For the latest caveats and feature information, see the Bug Search Tool at https:/​/​tools.cisco.com/​bugsearch/​ and the release notes for your software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the “New and Changed Information” chapter or the Feature History table below.

Information About VTP

Beginning with Cisco NX-OS Release 5.1(1), VTP and VTP pruning are supported for VTP version 1 and 2. Before Release 5.1(1), only VTP transparent mode was supported.


Note


Beginning with Cisco NX-OS Release 5.1(1), you can configure VLANs without actually creating the VLANs. For more details, see Configuring a VLAN Before Creating the VLAN.


VTP

VTP is a Layer 2 messaging protocol that maintains VLAN consistency by managing the addition, deletion, and renaming of VLANs within a VTP domain. A VTP domain is made up of one or more network devices that share the same VTP domain name and that are connected with trunk interfaces. Each network device can be in only one VTP domain.

Layer 2 trunk interfaces, Layer 2 port channels, and virtual port channels (vPCs) support VTP functionality.

The VTP is disabled by default on the device. You can enable and configure VTP using the command-line interface (CLI). When VTP is disabled, the device does not relay any VTP protocol packets.


Note


Before Release 5.1(1), VTP worked only in transparent mode in the Cisco Nexus 7000 Series devices, allowing you to extend a VTP domain across the device.


When the device is in the VTP transparent mode, the device relays all VTP protocol packets that it receives on a trunk port to all other trunk ports. When you create or modify a VLAN that is in VTP transparent mode, those VLAN changes affect only the local device. A VTP transparent network device does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements.


Note


VLAN 1 is required on all trunk ports used for switch interconnects if VTP is supported in the network. Disabling VLAN 1 from any of these ports prevents VTP from functioning properly.


If you enable VTP, you must configure either version 1 or version 2. If you are using VTP in a Token Ring environment, you must use version 2.

VTP Overview

VTP allows each router or LAN device to transmit advertisements in frames on its trunk ports. These frames are sent to a multicast address where they can be received by all neighboring devices. They are not forwarded by normal bridging procedures. An advertisement lists the sending device's VTP management domain, its configuration revision number, the VLANs which it knows about, and certain parameters for each known VLAN. By hearing these advertisements, all devices in the same management domain learn about any new VLANs that are configured in the transmitting device. This process allows you to create and configure a new VLAN only on one device in the management domain, and then that information is automatically learned by all the other devices in the same management domain.

Once a device learns about a VLAN, the device receives all frames on that VLAN from any trunk port by default, and if appropriate, forwards them to each of its other trunk ports, if any. This process prevents unnecessary VLAN traffic from being sent to a device. An extension of VTP called VTP pruning has been defined to limit the scope of broadcast traffic and save bandwidth. Beginning with Release 5.1(1), the Cisco NX-OS software supports VTP pruning.

VTP also publishes information about the domain and the mode in a shared local database that can be read by other processes such as Cisco Discovery Protocol (CDP).

VTP Modes

Beginning with Release 5.1(1), VTP is supported in these modes:

  • Transparent—Allows you to relay all VTP protocol packets that it receives on a trunk port to all other trunk ports. When you create or modify a VLAN that is in VTP transparent mode, those VLAN changes affect only the local device. A VTP transparent network device does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements. You cannot configure VLANs 1002 to 1005 in VTP client/server mode because these VLANs are reserved for Token Ring.
  • Server— Allows you to create, remove, and modify VLANs over the entire network. You can set other configuration options like the VTP version and also turn on or off 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 messages received over trunk links. Beginning with Release 5.1(1), the server mode is the default mode. The VLAN information is stored on the bootflash and is not erased after a reboot.
  • Client—VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client.
  • Off— Behaves similarly to the transparent mode but does not forward any VTP packets. The off mode allows you to monitor VLANs by using the CISCO-VTP-MIB without having to run VTP. On Cisco Nexus 7000 Series devices, because VTP is a conditional service, its MIB is loaded only when the corresponding feature is enabled. The CISCO-VTP-MIB does not follow this convention. It is loaded by the VLAN manager and will always return the correct values whether the VTP process is enabled or disabled.

Beginning with Cisco NX-OS Release 6.1(1), if VTP is in transparent or in off mode, you can configure VLAN long names of up to 128 characters. If VTP is in client or server mode, you cannot enable VLAN long-names. For more details, see the Configuring VLANs chapter.

VTP Per Interface

VTP allows you to enable or disable the VTP protocol on a per-port basis to control the VTP traffic. When a trunk is connected to a switch or end device, it drops incoming VTP packets and prevents VTP advertisements on this particular trunk. By default, VTP is enabled on all the switch ports.

VTP Pruning

The VLAN architecture requires all flooded traffic for a VLAN to be sent across a trunk port even if it leads to switches that have no devices that are active in the VLAN. This method leads to wasted network bandwidth.

VTP pruning optimizes the usage of network bandwidth by restricting the flooded traffic to only those trunk ports that can reach all the active network devices. When this protocol is in use, a trunk port does not receive the flooded traffic that is meant for a certain VLAN unless an appropriate join message is received.

A join message is defined as a new message type in addition to the ones already supported by version 1 of VTP. A VTP implementation indicates that it supports this extension by appending a special TLV at the end of the summary advertisement messages that it generates. In VTP transparent mode, VTP relays all VTP packets, and pruning requires that the switch processes TLVs in the VTP summary packets. You cannot use pruning in VTP transparent mode.

VTP Pruning and Spanning Tree Protocol

VTP maintains a list of trunk ports in the Spanning Tree Protocol (STP) forwarding state by querying STP at bootup and listening to the notifications that are generated by STP.

VTP sets a trunk port into the pruned or joined state by interacting with STP. STP notifies VTP when a trunk port goes to the blocking or forwarding state. VTP notifies STP when a trunk port becomes pruned or joined.

Default Settings

This table lists the default settings for VTP parameters.

Table 1 Default VTP Parameters

Parameters

Default

VTP

Disabled

VTP Mode

Transparent

VTP Domain

blank

VTP Version

1

VTP Pruning

Disabled

VTP per Interface

Enabled

Configuring VTP

You can configure VTP on Cisco NX-OS devices.


Note


VLAN 1 is required on all trunk ports used for switch interconnects if VTP is used in transparent mode in the network. Disabling VLAN 1 from any of these ports prevents VTP from functioning properly in transparent mode.



Note


Before Cisco NX-OS Release 5.1(1), VTP worked only in transparent mode.


Before You Begin

Ensure that you are in the correct virtual device context (VDC) (or enter the switchto vdc command). VLAN names and IDs can be repeated in different VDCs, so you must confirm which VDC that you are working in.

Procedure
     Command or ActionPurpose
    Step 1switch# configure terminal  

    Enters global configuration mode.

     
    Step 2switch(config)# feature vtp  

    Enables VTP on the device. The default is disabled.

     
    Step 3switch(config)# vtp domain domain-name  

    Specifies the name of the VTP domain that you want this device to join. The default is blank.

     
    Step 4switch(config)# vtp version {1 | 2}  

    Sets the VTP version that you want to use. The default is version 1.

     
    Step 5 switch(config)# vtp mode {client | server | transparent | off}  

    Sets the VTP mode to client, server, transparent, or off.

     
    Step 6switch(config)# vtp file file-name  

    Specifies the ASCII filename of the IFS file system file where the VTP configuration is stored.

     
    Step 7switch(config)# vtp password password-value  

    Specifies the password for the VTP administrative domain.

     
    Step 8switch(config)# exit  

    Exits the configuration submode.

     
    Step 9switch# show vtp status   (Optional)

    Displays information about the VTP configuration on the device, such as the version, mode, and revision number.

     
    Step 10switch# show vtp counters   (Optional)

    Displays information about VTP advertisement statistics on the device.

     
    Step 11 switch# show vtp interface   (Optional)

    Displays the list of VTP-enabled interfaces.

     
    Step 12switch# show vtp password   (Optional)

    Displays the password for the management VTP domain.

     
    Step 13switch# copy running-config startup-config   (Optional)

    Copies the running configuration to the startup configuration.

     

    This example shows how to configure VTP in transparent mode for the device:

    switch# configure terminal
    switch(config)# feature vtp 
    switch(config)# vtp domain accounting 
    switch(config)# vtp version 2 
    switch(config)# vtp mode transparent
    switch(config)# exit 
    switch#

    Configuring VTP Pruning

    You can configure VTP pruning on the Cisco NX-OS devices.

    Before You Begin

    You must enable VTP on the device.

    Procedure
       Command or ActionPurpose
      Step 1switch# configure terminal  

      Enters global configuration mode.

       
      Step 2 switch(config)# vtp pruning  

      Enables VTP pruning on the device. The default is disabled.

       
      Step 3 switch(config)# no vtp pruning   (Optional)

      Disables VTP pruning on the device. The default is disabled.

       
      Step 4 switch(config)# show interface interface-identifier switchport   (Optional)

      Displays the VTP pruning eligibility of the trunk port. The default is that all the VLANs from 2 to 1001 are pruning eligible.

       
      Step 5switch(config)# interface port-channel channel-number  

      Creates a port-channel interface and enter interface configuration mode.

       
      Step 6switch(config-if)# switchport trunk pruning vlan [add | remove | except | none | all] VLAN-IDs  

      Sets the specified VLANs to be VTP pruning eligible.

       
      Step 7switch(config-if)# end  

      returns to privileged EXEC mode.

       
      Step 8switch# show vtp counters   (Optional)

      Displays VTP pruning information and counters.

       
      Step 9 switch# clear vtp counters   (Optional)

      Resets all the VTP pruning counter values.

       

      This example shows how to set VLANs 9 to 54 to be pruning eligible and set VLANs 2 to 8 and 55 to 1001 as not eligible for VTP pruning:

      switch(config-if)# switchport trunk pruning vlan 9-54

      VLAN 1 is never pruning eligible, because it is a factory-default VLAN. VLANs 1002 to 1005 are reserved for Token Ring networks. The VLANs 1006 and above require VTP version 3 to be pruning eligible.