Troubleshooting of non-synchronous VLAN configuration information in VTP, vtpvlan

Troubleshooting of non-synchronous VLAN configuration information in VTP, vtpvlan

VTP (VLANTrunk Protocol, VLANTrunk Protocol) is a dedicated Cisco VLAN used to maintain and manage dynamic VLANs (such as VLAN Based on MAC addresses, IP addresses, network protocols, and VLAN management policies). It can be used to automatically transmit and exchange VLAN configuration information on the Trunk link, so that the VLAN configurations of switches in the same VTP domain are consistent.

The advantage of using VTP is that after you configure the required VLAN on a vswitch, The vswitch in the same VTP domain automatically creates the VLAN with the same ID, name, and configuration, this greatly reduces the workload for the Administrator to repeatedly create and configure VLANs, and reduces the number of configuration conflicts that may cause various problems, for example, duplicate VLAN names, incorrect VLAN types, and security configurations.

VTP uses the concept of a domain, that is, a VTP domain, including a group of switches that share the same VTP domain parameters (such as VTP domain names and VLAN configurations) in the network. You can create multiple VTP domains in the network, but one vswitch can only be in one VTP domain.

1. common causes of non-sync VLAN configuration information

• There is no vtp server in the corresponding VTP domain, or the VLAN to be synchronized by The VTP client is not manually created on the VTP SERVER

There must be at least one vtp server in a VTP domain. By default, all vswitches are in vtp server mode.

• The configuration revision number Of The VTP client is greater than the configuration revision number on the vtp server.
• The vlan id to be synchronized exceeds the range supported by The VTP version.

VTP 1 and VTP 2 can only advertise VLAN IDs in 1 ~ The basic VLAN in the range of 1005. VTP 3 only supports 1006 ~ 4094 notification of VLAN configuration extension in the range

• VTP announces transmission path interruption

There are vswitches that cannot forward VTP announcements from the vtp server To The VTP client, that is, their VTP is in off mode. In this case, these switches do not forward VLAN configuration information. Or some interfaces in the path cannot pass through the corresponding VLAN.

• The VTP domain name and password configured on The VTP client are not the same as those on The vtp server, or The VTP mode configuration is incorrect.

If the switch to synchronize VLAN information is configured in the transparent mode or Off mode, the VLAN configuration information cannot be synchronized.

• VTP versions of vswitches In The VTP domain are not compatible with each other.

Vswitches that only support VTP 1 cannot interact with vswitches that run VTP 2 or VTP 3. We recommend that you configure them to the same VTP version.

• VTP trim function blocked

When the VTP trim function is enabled, the corresponding VLAN configuration information is not sent when no device is connected to the corresponding VLAN under the corresponding Trunk interface.

2. troubleshooting of non-synchronous VLAN configuration information

As shown in, Switch 1 is configured in vtp server mode, and other switches are configured in VTP client mode.

Troubleshooting example of failure in VTP synchronous VLAN configuration information

Now, VLAN 10, VLAN 20, and VLAN 30 are manually created on Switch 1. Now, it is found that VLAN 10, VLAN 20, and VLAN 30 cannot be automatically created on Switch 6 through VTP.

The reason why the VTP client cannot synchronize VLAN configuration information is analyzed above. Of course, the vlan id (10, 20, 30) to be synchronized in this example is the basic range VLAN, all VTP versions support announcement, so we will only troubleshoot the causes of the other issues one by one (ShowAll commands are executed in privileged mode, and the check is stopped when the corresponding steps are executed to eliminate the fault)

 

Step 1: run the show vtp status Command on each vswitch to confirm that at least one vtp server switch is configured in the network, at least one vtp server switch must have a VLAN manually created for The VTP client switch to be synchronized. You can run the showvlan Command verification on this switch.

Switch1 #Showvtp status

VTP Version: 2

Configuration Revision: 1

Maximum VLANs supported locally: 1005

Number of existing VLANs: 6

VTP Operating Mode: Server

VTP Domain Name: test

VTP Pruning Mode: Disabled

VTP V2 Mode: Enabled

VTP Traps Generation: Disabled

MD5 digest: 0xDD 0x52 0x89 0xF5 0x75 0xB8 0xDA 0xFA

Configuration last modified by 0.0.0.0 at 3-1-9300: 59: 01

Local updater ID is 0.0.0.0 (novalid interface found)

 

Switch1 #Showvlan

 

VLAN Name Status Ports

----------------------------------------------------------------------------

1 default active Fa0/4, Fa0/5, Fa0/6, Fa0/7

Fa0/8, Fa0/9, Fa0/10, Fa0/11

Fa0/12, Fa0/13, Fa0/14, Fa0/15

Fa0/16, Fa0/17, Fa0/18, Fa0/19

Fa0/20, Fa0/21, Fa0/22, Fa0/23

Fa0/24, Gig0/1, Gig0/2

10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active

1002 fddi-default act/unsup

1003 token-ring-default act/unsup

1004 fddinet-default act/unsup

1005 trnet-default act/unsup

In this example, Switch 1 is configured as a vtp server Switch, and VLAN 10, VLAN 20, and VLAN 30 are manually created. If no, It is created on the vtp server.

Step 2: run the showvtp status Command on the VTP client and vtp server switch that cannot synchronize VLAN configuration information to view VTP configuration information.

In this step, first check their configuration revision numbers to verify that the configuration revision numbers of the Switch 6 VTP client that cannot synchronize VLAN configuration information are lower than the configuration revision numbers on the vtp server, it is best to set the VTP client configuration revision to 0 and make sure that the VTP domain name configured by the client is consistent with the VTP domain name configured on The vtp server switch, to ensure that the client switch can be successfully added to the VTP domain created on the vtp server.

Switch6 #Showvtp status

VTP Version: 2

Configuration Revision: 0

Maximum VLANs supported locally: 255

Number of existing VLANs: 5

VTP Operating Mode: Client

VTP Domain Name:

VTP Pruning Mode: Disabled

VTP V2 Mode: Disabled

VTP Traps Generation: Disabled

MD5 digest: 0x7D 0x5A 0xA6 0x0E 0x9A 0x72 0xA0 0x3A

Configuration last modified by 0.0.0.0 at 0-0-

Local updater ID is 0.0.0.0 (novalid interface found)

If the configuration revision number on the VTP client switch is no less than the revision number on the vtp server switch, run the following command on the VTP client switch:

(1)Configureterminal

(2)Vtp domainXXX

XXX here is any domain name different from the original VTP domain name, which is equivalent to modifying the VTP domain name of this switch. Because a vswitch can only have one VTP domain, the new VTP domain name will directly replace the original domain name. The purpose is to restore the configuration revision number to the default 0.

(3)End# --- Return directly to privileged Mode

(4)Show vtp status

Check whether the configuration revision number has been restored to 0.

(5)Vtp domainXxxx

Xxxx here is the VTP domain name created by the original client switch, that is, it is consistent with the VTP domain name configured on The vtp server switch.

(6)End

(7)Show vtp status

Confirm that the configuration revision number after the VTP domain is re-added has been restored to 0. At this time, the client can successfully join The VTP domain configured by the vtp server switch.

Step 3 use the show vtp status and show running-config interface commands to verify that all vswitches can forward VLAN configuration information packets.

It includes three layers. First, no VTP off mode can be configured through the switch, and VLAN configuration information can be forwarded in other three modes. Second, if the corresponding vtp server switch is VTP 3, you cannot disable VTP on the Trunk interface that reaches the VTP client switch path, third, the Trunk interface must exist in the path from The vtp server to the Switch 6 VTP client that cannot synchronize VLAN configuration information (only the Trunk interface can transmit VLAN configuration information ), and the VLAN to be synchronized must pass through.

 

Step 4. Run the showvtp status Command on the Switch 6 Switch that cannot synchronize configuration information to check whether the VTP configuration is correct and whether the VTP version is compatible with the VTP version of The vtp server.

This includes the VTP mode of Switch 6, The VTP domain name, And the password (must be consistent with the vtp server. Only the Server and Client modes can synchronize the VLAN configuration information sent from other VTP servers, Transparent and off) the VLAN configuration information of The vtp server cannot be synchronized.

In terms of version compatibility, vswitches that only support VTP 1 cannot interact with vswitches that support VTP2 and VTP 3, however, when VTP 2 and VTP 3 vswitches are configured as VTP 1, they can interact with VTP 2 and VTP 3 vswitches. Try not to configure VTP 1. Otherwise, we recommend that you configure VTP 1 for all vswitches In The VTP domain.

Switch6 #Showvtp status

VTP Version: 2

Configuration Revision: 0

Maximum VLANs supported locally: 255

Number of existing VLANs: 5

VTP Operating Mode: Client

VTP Domain Name: test

VTP Pruning Mode: Disabled

VTP V2 Mode: Disabled

VTP Traps Generation: Disabled

MD5 digest: 0x75 0x4A 0x67 0x29 0x54 0x7D 0x93 0xC4

Configuration last modified by0.0.0.0 at 0-0-00 00:00:00

 

Step 5: Use the show VTP status command on a device in the path from The vtp SERVER to the path where the VLAN configuration information cannot be synchronized to check whether any device has enabled the VTP trim function, run the showinterface trunk command to view the VLAN pruning configurations of each Trunk and check whether the VLAN to be synchronized has been trimmed.

Switch2 #Showvtp status

VTP Version: 2

Configuration Revision: 7

Maximum VLANs supported locally: 1005

Number of existing VLANs: 8

VTP Operating Mode: Client

VTP Domain Name: test

VTP Pruning Mode: Disabled

VTP V2 Mode: Disabled

VTP Traps Generation: Disabled

MD5 digest: 0xC7 0x2C 0x77 0x78 0x85 0x3B 0x00 0xF5

Configuration last modified by 0.0.0.0 at 3-1-9300: 01: 41

 

Switch2 #Show interface trunk

Port Mode Encapsulation Status Native vlan

Fa0/1 on 802.1q trunking 1

Fa0/2 on 802.1q trunking 1

Fa0/3 on 802.1q trunking 1

 

Port Vlans allowed on trunk

Fa0/1 1-1005

Fa0/2 1-1005

Fa0/3 1-1005

 

Port Vlans allowed and active in management domain

Fa0/1, 10, 20, 30

Fa0/2, 10, 20, 30

Fa0/3, 10, 20, 30

 

Port Vlans in spanning tree forwarding state and not pruned

Fa0/1, 10, 20, 30

Fa0/2, 10, 20, 30

Fa0/3, 10, 20, 30

If the VTP trim function or the VLAN configuration of the Trunk interface affects the transmission of VLAN configuration information, The VTP trim function is disabled on the corresponding device, cancel the VLAN trim configuration on the corresponding Trunk interface.

Through the above steps, you can find the cause of the fault and eliminate it. The result is displayed on the Switch 6 VTP client throughShow vlanCommand to view the three VLAN configurations created on the Switch 1 vtp server.

Switch6 #Showvlan

 

VLAN Name Status Ports

----------------------------------------------------------------------------

1 default active Fa0/2, Fa0/3, Fa0/4, Fa0/5

Fa0/6, Fa0/7, Fa0/8, Fa0/9

Fa0/10, Fa0/11, Fa0/12, Fa0/13

Fa0/14, Fa0/15, Fa0/16, Fa0/17

Fa0/18, Fa0/19, Fa0/20, Fa0/21

Fa0/22, Fa0/23, Fa0/24, Gig0/1

Gig0/2

10 VLAN0010 active

20 VLAN0020 active

30 VLAN0030 active

1002 fddi-default act/unsup

1003 token-ring-default act/unsup

1004 fddinet-default act/unsup

1005 trnet-default act/unsup

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