Virtual LANs VLAN Trunking Protocol (VLANs VTP)

Configuring Trunking Between a Catalyst 1900 and any Switch Running CatOS Software

Document ID: 24066

Updated: Nov 16, 2007



This document provides a sample configuration of InterSwitch Trunking (ISL trunk) between a Catalyst 1900 and a Catalyst 6500 switch running a CatOS image. The configuration is similar to other CatOS switches such as the Catalyst 5500 series switches. Relevant commands are highlighted for the configuration as well as show commands that help determine if the ISL trunk is functional.

Before You Begin


For more information on document conventions, see the Cisco Technical Tips Conventions.


Before attempting this configuration, please ensure that you meet the following prerequisites:

  • understanding VLAN concepts

  • understanding VLAN Trunk Protocol (VTP) concepts

Components Used

The information in this document is based on the software versions below.

  • Catalyst 1924-EN with software version (Enterprise) V9.00.05

  • Catalyst 6509 running CatOS with software version 7.3(2)

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.

Background Theory

The Catalyst 1900 runs two versions of images, namely the Standard and Enterprise editions. Trunking is only supported on the Enterprise images, and it only supports ISL encapsulation and does not support 802.1q. This limits the capability of the Catalyst 1900 to form a trunk with other Catalyst switches that can support ISL trunking. Furthermore, trunking can only be configured on the two x 100 Mbps uplink ports on the Catalyst 1900. These are the last two ports on the switch normally marked Ax and Bx. You can configure up to 1005 VLANs on the Catalyst 1900 Enterprise image. The Command Line Interface (CLI) (similar to the Cisco IOS® CLI) is only available on the Enterprise image of the Catalyst 1900.

Note: Catalyst 4000 series switches, with Supervisor I and II, and Catalyst 2950 series switches do not support ISL trunking and cannot be connected to the Catalyst 1900. Catalyst 5500 switches support ISL on certain modules. Issue the show port capabilities <mod/port> command to find out whether a specific module or port supports ISL trunking.


In this section, you are presented with the information to configure the features described in this document. For related configuration information, refer to the Default Settings and Configuration section of the Catalyst 1900/2820 Enterprise Edition SW Config Guide.

Trunking configuration can be accomplished in two ways, either through the menu or the CLI. The following example lists the configuration commands through the CLI mode:

Catalyst 1900 Management Console
Copyright (c) Cisco Systems, Inc. 1993-1999
All rights reserved.
Enterprise Edition Software
Ethernet Address: 00-E0-1E-87-36-C0

PCA Number: 73-2239-01
PCA Serial Number: 6510304
Model Number: WS-C1924-EN
System Serial Number: FAA0135Y00N
1 user(s) now active on Management Console.	
	User Interface Menu

	[M] Menus
	[K] Command Line

Enter Selection: K

CLI session with the switch is open.
To end the CLI session, enter [Exit].

Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .

Network Diagram

This document uses the network setup shown in the diagram below.



The basic steps of this configuration are as follows:

  1. Configure the VTP domain name and mode (such as one of the switches should at least be operating in the VTP server and the other in VTP client mode). For this document, set the VTP domain name as "DOC."

  2. Configure the trunking ports (go to the interface configuration and define the trunking parameters).

  3. Define the appropriate VLANs on the switch operating as a VTP server.

  4. Issue the appropriate show commands to verify the trunking operation.

There must be at least one VTP server in a domain. A VTP server can be configured on a Catalyst 6000 or a Catalyst 1900 switch. In this example, the Catalyst 6000 is configured as a VTP server, and the Catalyst 1900 is configured as a VTP client. This is because the Catalyst 6500 is more powerful than the Catalyst 1900, and therefore is better able to handle the server capabilities.

This document uses the configurations shown below:

  • Catalyst 6000

  • Catalyst 1924-EN

Catalyst 6000
Cat6000 (enable) show config
This command shows non-default configurations only.
Use 'show config all' to show both default and non-default configurations.


#time: Mon Nov 25 2002, 02:53:50 
#version 7.3(2)
set prompt Cat6000
set vtp domain DOC
set vlan 1 name default type ethernet mtu 1500 said 100001 state active 
set vlan 1002 name fddi-default type fddi mtu 1500 said 101002 state active 
set vlan 1004 name fddinet-default type fddinet mtu 1500 said 101004 state active
stp ieee 
set vlan 1005 name trnet-default type trbrf mtu 1500 said 101005 state active stp 
set vlan 2
set vlan 1003 name token-ring-default type trcrf mtu 1500 said 101003 state active
mode srb aremaxhop 7 stemaxhop 7 backupcrf off 

!--- Output suppressed.

#module 6 : 48-port 10/100BaseTX Ethernet
set trunk 6/1  desirable isl 1-1005,1025-4094

!--- Output suppressed.


Note: The trunk mode can be 802.1q or ISL. The ISL mode is used for the trunk port of the Catalyst 6000 because Catalyst 1900 supports ISL only.

Catalyst 1924-EN
Cat1924-EN#configure terminal

!--- Setup the VTP domain name.  Note that this is
!--- case sensitive and it must be identical with the domain
!--- name configured on the VTP server (Catalyst 6000).

Cat1924-EN(config)#vtp domain DOC

!--- To change the VTP mode to client. There are three VTP modes supported:
!--- server, transparent, and client.

Cat1924-EN(config)#vtp client 

!--- Set the interface up as a trunk port (this is interface Bx).

Cat1924-EN(config)#int fast0/27
Cat1924-EN(config-if)#trunk desirable 

Cat1924-EN#show run
Building configuration...
Current configuration:
vtp domain "DOC"
vtp client
vlan 2 name "VLAN0002" sde 100002 state Operational mtu 1500
hostname "Cat1924-EN"
interface Ethernet 0/27
 trunk Desirable

line console


This section provides information you can use to confirm that your configuration is working properly.

Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

Catalyst 1900

  • show vtp - this command verifies the VTP setup, as shown in the output below.

    Cat1924-EN#show vtp 
    VTP version: 1
    Configuration revision: 0
    Maximum VLANs supported locally: 1005
    Number of existing VLANs: 5
    VTP domain name : DOC
    VTP password : 
    VTP operating mode : Client
    VTP pruning mode : Disabled
    VTP traps generation : Enabled 
    Configuration last modified by: at 11-24-2002 19:41:22
  • show vtp statistics - this command checks for VTP advertisements, as shown in the output below.

    Cat1924-EN#show vtp statistics
    Receive Statistics Transmit Statistics
    ----------------------------------- -----------------------------------
    Summary Adverts 4 Summary Adverts 1
    Subset Adverts 3 Subset Adverts 0
    Advert Requests 0 Advert Requests 3
    Configuration Errors:
    Revision Errors 0  !non zero values indicates non-propagation of vlan changes (ie add/delete)  
    Digest Errors 0    !non zero values indicates mismatch in vtp password
    VTP Pruning Statistics:
    Port Join Received Join Transmitted Summary Adverts received
    with no pruning support
    ---- ------------- ---------------- ------------------------
    A 0 0 0 
    B 0 0 0 

Catalyst 6000

  • show trunk 6/1—this command verifies the trunk configuration, as shown in the output:

    Cat6000 (enable) show trunk 6/1
    * - indicates vtp domain mismatch
    Port      Mode         Encapsulation  Status        Native vlan
    --------  -----------  -------------  ------------  -----------
    6/1       desirable    isl            trunking      1
    Port      Vlans allowed on trunk
    --------  ---------------------------------------------------------------------
    6/1       1-1005,1025-4094
    Port      Vlans allowed and active in management domain 
    --------  ---------------------------------------------------------------------
    6/1       1-3
    Port      Vlans in spanning tree forwarding state and not pruned
    --------  ---------------------------------------------------------------------
    6/1       1-3
  • show vtp domain—This command verifies the VTP configuration, as shown in the output:

    Cat6000 (enable) show vtp domain
    Domain Name                      Domain Index VTP Version Local Mode  Password
    -------------------------------- ------------ ----------- ----------- ----------
    DOC                              1            2           server      -
    Vlan-count Max-vlan-storage Config Revision Notifications
    ---------- ---------------- --------------- -------------
    8          1023             2               disabled
    Last Updater    V2 Mode  Pruning  PruneEligible on Vlans
    --------------- -------- -------- -------------------------     disabled disabled 2-1000
  • show vtp statistics—This command verifies the VTP statistics, as shown in the output:

    Cat6000 (enable) show vtp statistics 
    VTP statistics:
    summary advts received 1
    subset advts received 0
    request advts received 1
    summary advts transmitted 89
    subset advts transmitted 5
    request advts transmitted 0
    No of config revision errors 0
    No of config digest errors 0
    VTP pruning statistics:
    Trunk    Join Transmitted Join Received Summary advts received from GVRP PDU
                                            non-pruning-capable device  Received
    -------- ---------------- ------------- --------------------------- ----------
    15/1     0                0             0                           0         


This section provides information you can use to troubleshoot your configuration.

Troubleshooting Procedure

This is troubleshooting information relevant to this configuration. Complete these steps in order to troubleshoot trunking between the switches.

  1. The VTP domain name must be identical (the VTP domain name is case sensitive).

  2. The VTP password must be identical.

  3. There must be at least one switch configured as the VTP server in the VTP domain.

  4. There can be more than one VTP client in a VTP domain.

    Note: Steps 1 and 2 can be verified if you issue the show vtp domain command. If there is a mismatch of results in any of the steps, VTP trunking does not work.

Related Information

Updated: Nov 16, 2007
Document ID: 24066