Consolidated Platform Configuration Guide, Cisco IOS XE 3.3SE (Catalyst 3850 Switches)
Configuring VTP
Downloads: This chapterpdf (PDF - 1.58MB) The complete bookPDF (PDF - 30.5MB) | Feedback

Contents

Configuring VTP

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http:/​/​www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Prerequisites for VTP

Before you create VLANs, you must decide whether to use the VLAN Trunking Protocol (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 is designed to work in an environment where updates are made on a single switch and are sent through VTP to other switches in the domain. It does not work well in a situation where multiple updates to the VLAN database occur simultaneously on switches in the same domain, which would result in an inconsistency in the VLAN database.

The switch supports a total of 4094 VLANs. However, the number of routed ports, SVIs, and other configured features affects the usage of the switch hardware. If the switch is notified by VTP of a new VLAN and the switch is already using the maximum available hardware resources, it sends a message that there are not enough hardware resources available and shuts down the VLAN. The output of the show vlan user EXEC command shows the VLAN in a suspended state.

Because trunk ports send and receive VTP advertisements, you must ensure that at least one trunk port is configured on the switch or switch stack and that this trunk port is connected to the trunk port of another switch. Otherwise, the switch cannot receive any VTP advertisements.

Restrictions for VTP

The following are restrictions for a VTP:

  • You cannot have a switch stack containing a mix of Catalyst 3850 and Catalyst 3650 switches.

Caution


Before adding a VTP client switch to a VTP domain, always verify that its VTP configuration revision number is lower than the configuration revision number of the other switches in the VTP domain. Switches in a VTP domain always use the VLAN configuration of the switch with the highest VTP configuration revision number. If you add a switch that has a revision number higher than the revision number in the VTP domain, it can erase all VLAN information from the VTP server and VTP domain.


Information About VTP

VTP

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.

VTP functionality is supported across the stack, and all switches in the stack maintain the same VLAN and VTP configuration inherited from the active switch. When a switch learns of a new VLAN through VTP messages or when a new VLAN is configured by the user, the new VLAN information is communicated to all switches in the stack.

When a switch joins the stack or when stacks merge, the new switches get VTP information from the active switch.

VTP Domain

A VTP domain (also called a VLAN management domain) consists of one switch or several interconnected switches or switch stacks under the same administrative responsibility sharing the same VTP domain name. A switch can be in only one VTP domain. You make global VLAN configuration changes for the domain.

By default, the switch is in the VTP no-management-domain state until it receives an advertisement for a domain over a trunk link (a link that carries the traffic of multiple VLANs) or until you configure a domain name. Until the management domain name is specified or learned, you cannot create or modify VLANs on a VTP server, and VLAN information is not propagated over the network.

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 then ignores advertisements with a different domain name or an earlier configuration revision number.

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 sent over all IEEE trunk connections, including IEEE 802.1Q. VTP dynamically maps VLANs with unique names and internal index associates across multiple LAN types. Mapping eliminates excessive device administration required from network administrators.

If you configure a switch for VTP transparent mode, you can create and modify VLANs, but the changes are not sent to other switches in the domain, and they affect only the individual switch. However, configuration changes made when the switch is in this mode are saved in the switch running configuration and can be saved to the switch startup configuration file.

Related References

VTP Modes

Table 1 VTP Modes

VTP Mode

Description

VTP server

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

VTP server is the default mode.

In VTP server mode, VLAN configurations are saved in NVRAM. If the switch detects a failure while writing a configuration to NVRAM, VTP mode automatically changes from server mode to client mode. If this happens, the switch cannot be returned to VTP server mode until the NVRAM is functioning.

VTP client

A VTP client functions like a VTP server and transmits and receives VTP updates on its trunks, but you cannot create, change, or delete VLANs on a VTP client. VLANs are configured on another switch in the domain that is in server mode.

In VTP versions 1 and 2 in VTP client mode, VLAN configurations are not saved in NVRAM. In VTP version 3, VLAN configurations are saved in NVRAM in client mode.

VTP transparent

VTP 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 or version 3, transparent switches do forward VTP advertisements that they receive from other switches through their trunk interfaces. You can create, modify, and delete VLANs on a switch in VTP transparent mode.

When the switch is in VTP transparent mode, the VTP and VLAN configurations are saved in NVRAM, but they are not advertised to other switches. In this mode, VTP mode and domain name are saved in the switch running configuration, and you can save this information in the switch startup configuration file by using the copy running-config startup-config privileged EXEC command.

In a switch stack, the running configuration and the saved configuration are the same for all switches in a stack.

VTP off

A switch in VTP off mode functions in the same manner as a VTP transparent switch, except that it does not forward VTP advertisements on trunks.

Related References

VTP Advertisements

Each switch in the VTP domain sends periodic global configuration advertisements from each trunk port to a reserved multicast address. Neighboring switches receive these advertisements and update their VTP and VLAN configurations as necessary.

VTP advertisements distribute this global domain information:

  • VTP domain name
  • VTP configuration revision number
  • Update identity and update timestamp
  • MD5 digest VLAN configuration, including maximum transmission unit (MTU) size for each VLAN
  • Frame format

VTP advertisements distribute this VLAN information for each configured VLAN:

  • VLAN IDs (including IEEE 802.1Q)
  • VLAN name
  • VLAN type
  • VLAN state
  • Additional VLAN configuration information specific to the VLAN type

In VTP version 3, VTP advertisements also include the primary server ID, an instance number, and a start index.

Related References

VTP Version 2

If you use VTP in your network, you must decide which version of VTP to use. By default, VTP operates in version 1.

VTP version 2 supports these features that are not supported in version 1:

  • Token Ring support—VTP version 2 supports Token Ring Bridge Relay Function (TrBRF) and Token Ring Concentrator Relay Function (TrCRF) VLANs.
  • 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 when the switch is operating in VTP server mode.
  • Version-Dependent Transparent Mode—In VTP version 1, a VTP transparent switch inspects VTP messages for the domain name and version and forwards a message only if the version and domain name match. Although VTP version 2 supports only one domain, a VTP version 2 transparent switch forwards a message only when the domain name matches.
  • 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 MD5 digest on a received VTP message is correct, its information is accepted.

VTP Version 3

VTP version 3 supports these features that are not supported in version 1 or version 2:

  • Enhanced authentication—You can configure the authentication as hidden or secret. When hidden, the secret key from the password string is saved in the VLAN database file, but it does not appear in plain text in the configuration. Instead, the key associated with the password is saved in hexadecimal format in the running configuration. You must reenter the password if you enter a takeover command in the domain. When you enter the secret keyword, you can directly configure the password secret key.
  • Support for extended range VLAN (VLANs 1006 to 4094) database propagation—VTP versions 1 and 2 propagate only VLANs 1 to 1005.

    Note


    VTP pruning still applies only to VLANs 1 to 1005, and VLANs 1002 to 1005 are still reserved and cannot be modified.


  • Support for any database in a domain—In addition to propagating VTP information, version 3 can propagate Multiple Spanning Tree (MST) protocol database information. A separate instance of the VTP protocol runs for each application that uses VTP.
  • VTP primary server and VTP secondary servers—A VTP primary server updates the database information and sends updates that are honored by all devices in the system. A VTP secondary server can only back up the updated VTP configurations received from the primary server to its NVRAM. By default, all devices come up as secondary servers. You can enter the vtp primary privileged EXEC command to specify a primary server. Primary server status is only needed for database updates when the administrator issues a takeover message in the domain. You can have a working VTP domain without any primary servers. Primary server status is lost if the device reloads or domain parameters change, even when a password is configured on the switch.
  • The option to turn VTP on or off on a per-trunk (per-port) basis—You can enable or disable VTP per port by entering the [ no] vtp interface configuration command. When you disable VTP on trunking ports, all VTP instances for that port are disabled. You cannot set VTP to off for the MST database and on for the VLAN database on the same port. When you globally set VTP mode to off, it applies to all the trunking ports in the system. However, you can specify on or off on a per-VTP instance basis. For example, you can configure the switch as a VTP server for the VLAN database but with VTP off for the MST database.

VTP Pruning

VTP pruning increases network available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to reach the destination devices. Without VTP pruning, a switch floods broadcast, multicast, and unknown unicast traffic across all trunk links within a VTP domain even though receiving switches might discard them. VTP pruning is disabled by default.

VTP pruning blocks unneeded flooded traffic to VLANs on trunk ports that are included in the pruning-eligible list. Only VLANs included in the pruning-eligible list can be pruned. By default, VLANs 2 through 1001 are pruning eligible switch trunk ports. If the VLANs are configured as pruning-ineligible, the flooding continues. VTP pruning is supported in all VTP versions.

Figure 1. Flooding Traffic without VTP Pruning. VTP pruning is disabled in the switched network. Port 1 on Switch A and Port 2 on Switch D are assigned to the Red VLAN. If a broadcast is sent from the host connected to Switch A, Switch A floods the broadcast and every switch in the network receives it, even though Switches C, E, and F have no ports in the Red VLAN.



Figure 2. Optimized Flooded Traffic VTP Pruning. VTP pruning is enabled in the switched network. The broadcast traffic from Switch A is not forwarded to Switches C, E, and F because traffic for the Red VLAN has been pruned on the links shown (Port 5 on Switch B and Port 4 on Switch D).



Enabling VTP pruning on a VTP server enables pruning for the entire management domain. Making VLANs pruning-eligible or pruning-ineligible affects pruning eligibility for those VLANs on that trunk only (not on all switches in the VTP domain).

VTP pruning takes effect several seconds after you enable it. VTP pruning does not prune traffic from VLANs that are pruning-ineligible. VLAN 1 and VLANs 1002 to 1005 are always pruning-ineligible; traffic from these VLANs cannot be pruned. Extended-range VLANs (VLAN IDs higher than 1005) are also pruning-ineligible.

VTP and Switch Stacks

VTP configuration is the same in all members of a switch stack. When the switch stack is in VTP server, client, or transparent mode, all switches in the stack carry the same VTP configuration.

  • When a switch joins the stack, it inherits the VTP and VLAN properties of the active switch.
  • All VTP updates are carried across the stack.
  • When VTP mode is changed in a switch in the stack, the other switches in the stack also change VTP mode, and the switch VLAN database remains consistent.

VTP version 3 functions the same on a standalone switch or a stack except when the switch stack is the primary server for the VTP database. In this case, the MAC address of the active switch is used as the primary server ID. If the active switch reloads or is powered off, a new active switch is elected.

  • If you do not configure the persistent MAC address feature, when the new active switch is elected, it sends a takeover message using the current stack MAC address.

    Note


    By default the persistent MAC address is on.


VTP Configuration Guidelines

VTP Configuration Requirements

When you configure VTP, you must configure a trunk port so that the switch can send and receive VTP advertisements to and from other switches in the domain.

VTP Settings

The VTP information is saved in the VTP VLAN database. When VTP mode is transparent, the VTP domain name and mode are also saved in the switch running configuration file, and you can save it in the switch startup configuration file by entering the copy running-config startup-config privileged EXEC command. You must use this command if you want to save VTP mode as transparent, even if the switch resets.

When you save VTP information in the switch startup configuration file and reboot the switch, the switch configuration is selected as follows:

  • If the VTP mode is transparent in the startup configuration and the VLAN database and the VTP domain name from the VLAN database matches that in the startup configuration file, the VLAN database is ignored (cleared), and the VTP and VLAN configurations in the startup configuration file are used. The VLAN database revision number remains unchanged in the VLAN database.
  • If the VTP mode or domain name in the startup configuration do not match the VLAN database, the domain name and VTP mode and configuration for VLAN IDs 1 to 1005 use the VLAN database information.

Domain Names for Configuring VTP

When configuring VTP for the first time, you must always assign a domain name. You must configure all switches in the VTP domain with the same domain name. Switches in VTP transparent mode do not exchange VTP messages with other switches, and you do not need to configure a VTP domain name for  them.


Note


If the NVRAM and DRAM storage is sufficient, all switches in a VTP domain should be in VTP server mode.



Caution


Do not configure a VTP domain if all switches are operating in VTP client mode. If you configure the domain, it is impossible to make changes to the VLAN configuration of that domain. Make sure that you configure at least one switch in the VTP domain for VTP server mode.


Passwords for the VTP Domain

You can configure a password for the VTP domain, but it is not required. If you do configure a domain password, all domain switches must share the same password and you must configure the password on each switch in the management domain. Switches without a password or with the wrong password reject VTP advertisements.

If you configure a VTP password for a domain, a switch that is booted without a VTP configuration does not accept VTP advertisements until you configure it with the correct password. After the configuration, the switch accepts the next VTP advertisement that uses the same password and domain name in the advertisement.

If you are adding a new switch to an existing network with VTP capability, the new switch learns the domain name only after the applicable password has been configured on it.


Caution


When you configure a VTP domain password, the management domain does not function properly if you do not assign a management domain password to each switch in the domain.


VTP Version

Follow these guidelines when deciding which VTP version to implement:

  • All switches in a VTP domain must have the same domain name, but they do not need to run the same VTP version.
  • A VTP version 2-capable switch can operate in the same VTP domain as a switch running VTP version 1 if version 2 is disabled on the version 2-capable switch (version 2 is disabled by default).
  • If a switch running VTP version 1, but capable of running VTP version 2, receives VTP version 3 advertisements, it automatically moves to VTP version 2.
  • If a switch running VTP version 3 is connected to a switch running VTP version 1, the VTP version 1 switch moves to VTP version 2, and the VTP version 3 switch sends scaled-down versions of the VTP packets so that the VTP version 2 switch can update its database.
  • A switch running VTP version 3 cannot move to version 1 or 2 if it has extended VLANs.
  • Do not enable VTP version 2 on a switch unless all of the switches in the same VTP domain are version-2-capable. When you enable version 2 on a switch, all of the version-2-capable switches in the domain enable version 2. If there is a version 1-only switch, it does not exchange VTP information with switches that have version 2 enabled.
  • Cisco recommends placing VTP version 1 and 2 switches at the edge of the network because they do not forward VTP version 3 advertisements.
  • If there are TrBRF and TrCRF Token Ring networks in your environment, you must enable VTP version 2 or version 3 for Token Ring VLAN switching to function properly. To run Token Ring and Token Ring-Net, disable VTP version 2.
  • VTP version 1 and version 2 do not propagate configuration information for extended range VLANs (VLANs 1006 to 4094). You must configure these VLANs manually on each device. VTP version 3 supports extended-range VLANs and support for extended range VLAN database propagation.
  • When a VTP version 3 device trunk port receives messages from a VTP version 2 device, it sends a scaled-down version of the VLAN database on that particular trunk in VTP version 2 format. A VTP version 3 device does not send VTP version 2-formatted packets on a trunk unless it first receives VTP version 2 packets on that trunk port.
  • When a VTP version 3 device detects a VTP version 2 device on a trunk port, it continues to send VTP version 3 packets, in addition to VTP version 2 packets, to allow both kinds of neighbors to coexist on the same trunk.
  • A VTP version 3 device does not accept configuration information from a VTP version 2 or version 1 device.
  • Two VTP version 3 regions can only communicate in transparent mode over a VTP version 1 or version 2 region.
  • Devices that are only VTP version 1 capable cannot interoperate with VTP version 3 devices.
  • VTP version 1 and version 2 do not propagate configuration information for extended range VLANs (VLANs 1006 to 4094). You must manually configure these VLANs on each device.
  • If you configure the switch for VTP client mode, the switch does not create the VLAN database file (vlan.dat). If the switch is then powered off, it resets the VTP configuration to the default. To keep the VTP configuration with VTP client mode after the switch restarts, you must first configure the VTP domain name before the VTP mode.

    Caution


    If all switches are operating in VTP client mode, do not configure a VTP domain name. If you do, it is impossible to make changes to the VLAN configuration of that domain. Therefore, make sure you configure at least one switch as a VTP server.


How to Configure VTP

Configuring VTP Mode (CLI)

You can configure VTP mode as one of these:

  • VTP server mode—In VTP server mode, you can change the VLAN configuration and have it propagated throughout the network.
  • VTP client mode—In VTP client mode, you cannot change its VLAN configuration. The client switch receives VTP updates from a VTP server in the VTP domain and then modifies its configuration accordingly.
  • VTP transparent mode—In VTP transparent mode, VTP is disabled on the switch. The switch does not send VTP updates and does not act on VTP updates received from other switch. However, a VTP transparent switch running VTP version 2 does forward received VTP advertisements on its trunk links.
  • VTP off mode—VTP off mode is the same as VTP transparent mode except that VTP advertisements are not forwarded.

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

SUMMARY STEPS

    1.    configure terminal

    2.    vtp domain domain-name

    3.    vtp mode { client | server | transparent | off} { vlan | mst | unknown}

    4.    vtp password password

    5.    end

    6.    show vtp status

    7.    copy running-config startup-config


DETAILED STEPS
      Command or Action Purpose
    Step 1 configure terminal


    Example:
    
                
              
    Switch# configure terminal
    
    
     

    Enters the global configuration mode.

     
    Step 2 vtp domain domain-name


    Example:
    
                
              
    Switch(config)# vtp domain eng_group
    
    
     

    Configures the VTP administrative-domain name. The name can be 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.

    This command is optional for modes other than server mode. VTP server mode requires a domain name. If the switch has a trunk connection to a VTP domain, the switch learns the domain name from the VTP server in the domain.

    You should configure the VTP domain before configuring other VTP parameters.

    Note   
     
    Step 3 vtp mode { client | server | transparent | off} { vlan | mst | unknown}


    Example:
    
                
              
    Switch(config)# vtp mode server
    
    
     

    Configures the switch for VTP mode (client, server, transparent, or off).

    • vlan—The VLAN database is the default if none are configured.
    • mst—The multiple spanning tree (MST) database.
    • unknown—An unknown database type.
     
    Step 4 vtp password password


    Example:
    
                
              
    Switch(config)#  
                vtp password mypassword
    
    
     

    (Optional) Sets the password for the VTP domain. The password can be 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.

     
    Step 5 end


    Example:
    
                
              
    Switch(config)# end
    
    
     

    Returns to privileged EXEC mode.

     
    Step 6 show vtp status


    Example:
    
                
              
    Switch# show vtp status
    
    
     

    Verifies your entries in the VTP Operating Mode and the VTP Domain Name fields of the display.

     
    Step 7 copy running-config startup-config


    Example:
    
                
              
    Switch# copy running-config startup-config
    
    
     

    (Optional) Saves the configuration in the startup configuration file.

    Only VTP mode and domain name are saved in the switch running configuration and can be copied to the startup configuration file.

     
    Related References

    Configuring a VTP Version 3 Password (CLI)

    You can configure a VTP version 3 password on the switch.

    SUMMARY STEPS

      1.    configure terminal

      2.    vtp password password [ hidden | secret]

      3.    end

      4.    show vtp password

      5.    copy running-config startup-config


    DETAILED STEPS
        Command or Action Purpose
      Step 1 configure terminal


      Example:
      
                  
                
      Switch# configure terminal
      
      
       

      Enters the global configuration mode.

       
      Step 2 vtp password password [ hidden | secret]


      Example:
      
                  
                
      Switch(config)# vtp password mypassword hidden
      
      
       

      (Optional) Sets the password for the VTP domain. The password can be 8 to 64 characters.

      • (Optional) hidden—Saves the secret key generated from the password string in the nvram:vlan.dat file. If you configure a takeover by configuring a VTP primary server, you are prompted to reenter the password.
      • (Optional) secret—Directly configures the password. The secret password must contain 32 hexadecimal characters.
       
      Step 3 end


      Example:
      
                  
                
      Switch(config)# end
      
      
       

      Returns to privileged EXEC mode.

       
      Step 4 show vtp password


      Example:
      
                  
                
      Switch# show vtp password
      
      
       

      Verifies your entries. The output appears like this:

      VTP password: 89914640C8D90868B6A0D8103847A733

       
      Step 5 copy running-config startup-config


      Example:
      
                  
                
      Switch# copy running-config startup-config
      
      
       

      (Optional) Saves the configuration in the startup configuration file.

       
      Related Concepts

      Configuring a VTP Version 3 Primary Server (CLI)

      When you configure a VTP server as a VTP primary server, the takeover operation starts.

      SUMMARY STEPS

        1.    vtp primary [ vlan | mst] [ force]


      DETAILED STEPS
          Command or Action Purpose
        Step 1 vtp primary [ vlan | mst] [ force]


        Example:
        
                    
                  
        Switch# vtp primary vlan force
        
         

        Changes the operational state of a switch from a secondary server (the default) to a primary server and advertises the configuration to the domain. If the switch password is configured as hidden, you are prompted to reenter the password.

        • (Optional) vlan—Selects the VLAN database as the takeover feature. This is the default.
        • (Optional) mst—Selects the multiple spanning tree (MST) database as the takeover feature.
        • (Optional) force—Overwrites the configuration of any conflicting servers. If you do not enter force, you are prompted for confirmation before the takeover.
         
        Related Concepts

        Enabling the VTP Version (CLI)

        VTP version 2 and version 3 are disabled by default.

        • When you enable VTP version 2 on a switch , every VTP version 2-capable switch in the VTP domain enables version 2. To enable VTP version 3, you must manually configure it on each switch .
        • With VTP versions 1 and 2, you can configure the version only on switches in VTP server or transparent mode. If a switch is running VTP version 3, you can change to version 2 when the switch is in client mode if no extended VLANs exist, and no hidden password was configured.

          Caution


          VTP version 1 and VTP version 2 are not interoperable on switches in the same VTP domain. Do not enable VTP version 2 unless every switch in the VTP domain supports version 2.


        • In TrCRF and TrBRF Token Ring environments, you must enable VTP version 2 or VTP version 3 for Token Ring VLAN switching to function properly. For Token Ring and Token Ring-Net media, disable VTP version 2.

          Caution


          In VTP version 3, both the primary and secondary servers can exist on an instance in the domain.


        SUMMARY STEPS

          1.    configure terminal

          2.    vtp version { 1 | 2 | 3}

          3.    end

          4.    show vtp status

          5.    copy running-config startup-config


        DETAILED STEPS
            Command or Action Purpose
          Step 1 configure terminal


          Example:
          
                      
                    
          Switch# configure terminal
          
          
           

          Enters the global configuration mode.

           
          Step 2 vtp version { 1 | 2 | 3}


          Example:
          
                      
                    
          Switch(config)# vtp version 2
          
          
           

          Enables the VTP version on the switch. The default is VTP version 1.

           
          Step 3 end


          Example:
          
                      
                    
          Switch(config)# end
          
          
           

          Returns to privileged EXEC mode.

           
          Step 4 show vtp status


          Example:
          
                      
                    
          Switch# show vtp status
          
          
           

          Verifies that the configured VTP version is enabled.

           
          Step 5 copy running-config startup-config


          Example:
          
                      
                    
          Switch# copy running-config startup-config
          
          
           

          (Optional) Saves the configuration in the startup configuration file.

           

          Enabling VTP Pruning (CLI)

          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.

          With VTP versions 1 and 2, when you enable pruning on the VTP server, it is enabled for the entire VTP domain. In VTP version 3, you must manually enable pruning on each switch in the 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.

          Before You Begin

          VTP pruning is not designed to function in VTP transparent mode. If one or more switches in the network are in VTP transparent mode, you should do one of these actions:

          • Turn off VTP pruning in the entire network.
          • Turn off VTP pruning by making all VLANs on the trunk of the switch upstream to the VTP transparent switch pruning ineligible.

          To configure VTP pruning on an interface, use the switchport trunk pruning vlan interface configuration command. VTP pruning operates when an interface is trunking. You can set VLAN pruning-eligibility, whether or not VTP pruning is enabled for the VTP domain, whether or not any given VLAN exists, and whether or not the interface is currently trunking.

          SUMMARY STEPS

            1.    configure terminal

            2.    vtp pruning

            3.    end

            4.    show vtp status


          DETAILED STEPS
              Command or Action Purpose
            Step 1 configure terminal


            Example:
            
                        
                      
            Switch# configure terminal
            
            
             

            Enters the global configuration mode.

             
            Step 2 vtp pruning


            Example:
            
                        
                      
            Switch(config)# vtp pruning
            
            
             

            Enables pruning in the VTP administrative domain.

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

             
            Step 3 end


            Example:
            
                        
                      
            Switch(config)# end
            
            
             

            Returns to privileged EXEC mode.

             
            Step 4 show vtp status


            Example:
            
                        
                      
            Switch# show vtp status
            
            
             

            Verifies your entries in the VTP Pruning Mode field of the display.

             
            Related Concepts

            Configuring VTP on a Per-Port Basis (CLI)

            With VTP version 3, you can enable or disable VTP on a per-port basis. You can enable VTP only on ports that are in trunk mode. Incoming and outgoing VTP traffic are blocked, not forwarded.

            SUMMARY STEPS

              1.    configure terminal

              2.    interface interface-id

              3.    vtp

              4.    end

              5.    show running-config interface interface-id

              6.    show vtp status


            DETAILED STEPS
                Command or Action Purpose
              Step 1 configure terminal


              Example:
              
                          
                        
              Switch# configure terminal
              
              
               

              Enters the global configuration mode.

               
              Step 2 interface interface-id


              Example:
              
                          
                        
              Switch(config)# interface gigabitethernet1/0/1
              
              
               

              Identifies an interface, and enters interface configuration mode.

               
              Step 3 vtp


              Example:
              
                          
                        
              Switch(config)# vtp
              
              
               

              Enables VTP on the specified port.

               
              Step 4 end


              Example:
              
                          
                        
              Switch(config)# end
              
              
               

              Returns to privileged EXEC mode.

               
              Step 5 show running-config interface interface-id


              Example:
              
                          
                        
              Switch# show running-config interface gigabitethernet1/0/1
              
              
               

              Verifies the change to the port.

               
              Step 6 show vtp status


              Example:
              
                          
                        
              Switch# show vtp status
              
              
               

              Verifies the configuration.

               
              Related Concepts

              Adding a VTP Client Switch to a VTP Domain (CLI)

              Follow these steps to verify and reset the VTP configuration revision number on a switch before adding it to a VTP domain.

              Before You Begin

              Before adding a VTP client to a VTP domain, always verify that its VTP configuration revision number is lower than the configuration revision number of the other switches in the VTP domain. Switches in a VTP domain always use the VLAN configuration of the switch with the highest VTP configuration revision number. With VTP versions 1 and 2, adding a switch that has a revision number higher than the revision number in the VTP domain can erase all VLAN information from the VTP server and VTP domain. With VTP version 3, the VLAN information is not erased.

              You can use the vtp mode transparent global configuration command to disable VTP on the switch and then to change its VLAN information without affecting the other switches in the VTP domain.

              SUMMARY STEPS

                1.    show vtp status

                2.    configure terminal

                3.    vtp domain domain-name

                4.    end

                5.    show vtp status

                6.    configure terminal

                7.    vtp domain domain-name

                8.    end

                9.    show vtp status


              DETAILED STEPS
                  Command or Action Purpose
                Step 1 show vtp status


                Example:
                
                            
                          
                Switch# show vtp status
                
                
                 

                Checks the VTP configuration revision number.

                If the number is 0, add the switch to the VTP domain.

                If the number is greater than 0, follow these substeps:

                • Write down the domain name.
                • Write down the configuration revision number.
                • Continue with the next steps to reset the switch configuration revision number.
                 
                Step 2 configure terminal


                Example:
                
                            
                          
                Switch# configure terminal
                
                
                 

                Enters the global configuration mode.

                 
                Step 3 vtp domain domain-name


                Example:
                
                            
                          
                Switch(config)# vtp domain domain123
                
                
                 

                Changes the domain name from the original one displayed in Step 1 to a new name.

                 
                Step 4 end


                Example:
                
                            
                          
                Switch(config)# end
                
                
                 

                Returns to privileged EXEC mode. The VLAN information on the switch is updated and the configuration revision number is reset to 0.

                 
                Step 5 show vtp status


                Example:
                
                            
                          
                Switch# show vtp status
                
                
                 

                Verifies that the configuration revision number has been reset to 0.

                 
                Step 6 configure terminal


                Example:
                
                            
                          
                Switch# configure terminal
                
                
                 

                Enters global configuration mode.

                 
                Step 7 vtp domain domain-name


                Example:
                
                            
                          
                Switch(config)# vtp domain domain012
                
                
                 

                Enters the original domain name on the switch

                 
                Step 8 end


                Example:
                
                            
                          
                Switch(config)# end
                
                
                 

                Returns to privileged EXEC mode. The VLAN information on the switch is updated.

                 
                Step 9 show vtp status


                Example:
                
                            
                          
                Switch# show vtp status
                
                
                 

                (Optional) Verifies that the domain name is the same as in Step 1 and that the configuration revision number is 0.

                 
                Related References

                Monitoring VTP

                This section describes commands used to display and monitor the VTP configuration.

                You monitor VTP by displaying VTP configuration information: the domain name, the current VTP revision, and the number of VLANs. You can also display statistics about the advertisements sent and received by the switch.

                Table 2 VTP Monitoring Commands

                Command

                Purpose

                show vtp counters

                Displays counters about VTP messages that have been sent and received.

                show vtp devices [ conflict]

                Displays information about all VTP version 3 devices in the domain. Conflicts are VTP version 3 devices with conflicting primary servers. The show vtp devices command does not display information when the switch is in transparent or off mode.

                show vtp interface [ interface-id]

                Displays VTP status and configuration for all interfaces or the specified interface.

                show vtp password

                Displays the VTP password. The form of the password displayed depends on whether or not the hidden keyword was entered and if encryption is enabled on the switch.

                show vtp status

                Displays the VTP switch configuration information.

                Configuration Examples for VTP

                Example: Configuring a Switch as the Primary Server

                This example shows how to configure a switch as the primary server for the VLAN database (the default) when a hidden or secret password was configured:

                
                         
                       
                Switch#  
                         vtp primary vlan
                Enter VTP password:  
                         mypassword
                This switch is becoming Primary server for vlan feature in the VTP  domain
                
                VTP Database Conf Switch ID      Primary Server Revision System Name
                ------------ ---- -------------- -------------- -------- --------------------
                VLANDB       Yes  00d0.00b8.1400=00d0.00b8.1400 1        stp7
                
                Do you want to continue (y/n) [n]? y
                
                
                Related Concepts

                Where to Go Next

                After configuring VTP, you can configure the following:

                • VLANs
                • VLAN groups
                • VLAN trunking
                • Voice VLANs

                Additional References

                Related Documents

                Related Topic Document Title

                For complete syntax and usage information for the commands used in this chapter.

                VLAN Command Reference (Catalyst 3850 Switches)

                Layer 2/3 Command Reference (Catalyst 3850 Switches)

                Additional configuration commands and procedures.

                LAN Switching Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3850 Switches)

                Layer 2/3 Configuration Guide (Catalyst 3850 Switches)

                Error Message Decoder

                Description Link

                To help you research and resolve system error messages in this release, use the Error Message Decoder tool.

                https:/​/​www.cisco.com/​cgi-bin/​Support/​Errordecoder/​index.cgi

                Standards and RFCs

                Standard/RFC Title

                RFC 1573

                Evolution of the Interfaces Group of MIB-II

                RFC 1757

                Remote Network Monitoring Management

                RFC 2021

                SNMPv2 Management Information Base for the Transmission Control Protocol using SMIv2

                MIBs

                MIB MIBs Link

                All supported MIBs for this release.

                To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

                http:/​/​www.cisco.com/​go/​mibs

                Technical Assistance

                Description Link

                The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

                To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

                Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

                http:/​/​www.cisco.com/​support

                Feature History and Information for VTP

                Release

                Modification

                Cisco IOS XE 3.2SE

                This feature was introduced.