7 Replies Latest reply: May 17, 2012 2:59 PM by chemilio RSS

    VTP question

    Dada

      Hi,

       

      As per the VTP policy we cant create VLANs when the switch is in client mode....Assume that we have changed the mode to transparent and created new VLAN and again changed the mode back to client mode...Will the switch have a higher revision number and replicate the new VLAN changes to all switches in same domain? please clarify...

        • 1. Re: VTP question
          Rimantas

          I think switches with client mode cant replicate own VLANs

          • 2. Re: VTP question
            Elvin Arias

            Remember that VTP transparent mode is the only mode that doesn't increase the revision number, meaning that this field is always set to zero. So when you convert the switch from client to transparent to create the VLANs you will not be able to increase the revision no matter the changes you do on your switch configuration, and when you turn your switch back to client mode again it will be updated from other VTP client or server mode switch with a higher revision number.

             

            One of the differences between a VTP client and a VTP server mode switch is the VLAN creation and deletion capability, but  the messages are propagated in the same way, so a client can still update a server if it's revision number is higher.

             

            Elvin

            • 3. Re: VTP question
              John

              Hi

               

              When you move it to transparent mode it resets it to revision zero, that is what you would want to do if you wanted to add a switch that had a higher revision number than the network has now and you did not want to destroy your network I.E. change it to transparent and then change it to client/server. You can also change the domain name to something other that the domain name in use now then change it back again.

               

               

               

              Regards

              John

              • 4. Re: VTP question
                alfonz

                Hi!

                 

                The switch vlan (normal range) database is stored on the flash in vlan.dat file.

                 

                In the vtp client mode the content of the file can be syncronised with another switches in the vtp domian.

                 

                If you change the client mode to transparent, then you stop the syncronisation process and clear the revision number counter to zero. (From this point the switch will relay the received vlan information only.)

                 

                You can modify the vlan.dat file by adding a new VLAN. During this activity the revision counter does not increase from the zero value.

                 

                If you change the vtp mode to client, the vlan.dat file can be syncronised in

                 

                the domain again. If the vtp domain name, vtp password are the same and the revision number is the highest (in this case it's zero), then the modified configuration can get valid on the switches of the domain.

                 

                In your scenario the issued vtp advertisment can't become valid

                because it has the lowest revison number as possible.

                 

                I think the switch is getting a vtp advertisment with higher revision number, and the previously modified vlan.dat file will be updated soon.

                • 5. Re: VTP question
                  Steven Williams

                  Usually when you put a switch in transparent mode and create vlans on that switch, you want those vlans to say local to that switch.

                  • 7. Re: VTP question
                    chemilio

                    Hi dada,

                     

                    So lets start with a switch in VTP mode client.

                     

                    SW4-2590#sh vtp status

                    VTP Version                     : 2

                    Configuration Revision          : 14

                    Maximum VLANs supported locally : 250

                    Number of existing VLANs        : 6

                    VTP Operating Mode              : Client

                    VTP Domain Name                 : CISCO

                    VTP Pruning Mode                : Disabled

                    VTP V2 Mode                     : Disabled

                    VTP Traps Generation            : Disabled

                    MD5 digest                      : 0xF9 0x7D 0xCD 0x8B 0xE0 0x58 0x20 0x1E

                    Configuration last modified by 192.168.1.1 at 3-1-93 00:34:55

                     

                    Then change to VTP mode transparent

                     

                    SW4-2590(config)#vtp mode transparent

                    Setting device to VTP TRANSPARENT mode.

                     

                    SW4-2590(config)#do show vtp status

                    VTP Version                     : 2

                    Configuration Revision          : 0

                    Maximum VLANs supported locally : 250

                    Number of existing VLANs        : 6

                    VTP Operating Mode              : Transparent

                    VTP Domain Name                 : CISCO

                    VTP Pruning Mode                : Disabled

                    VTP V2 Mode                     : Disabled

                    VTP Traps Generation            : Disabled

                    MD5 digest                      : 0xF9 0x7D 0xCD 0x8B 0xE0 0x58 0x20 0x1E

                    Configuration last modified by 192.168.1.1 at 3-1-93 00:34:55

                     

                    Then while in tranparent mode add a vlan 20 which is unique only to the transparent switch.

                     

                    W4-2590(config)#vlan 20

                    SW4-2590(config-vlan)#end

                     

                    SW4-2590#sh vtp status

                    VTP Version                     : 2

                    Configuration Revision          : 0

                    Maximum VLANs supported locally : 250

                    Number of existing VLANs        : 7

                    VTP Operating Mode              : Transparent

                    VTP Domain Name                 : CISCO

                    VTP Pruning Mode                : Disabled

                    VTP V2 Mode                     : Disabled

                    VTP Traps Generation            : Disabled

                    MD5 digest                      : 0x74 0x25 0x17 0x0D 0x01 0xFD 0x29 0x93

                    Configuration last modified by 192.168.12.1 at 3-1-93 00:34:55

                     

                    Then lets change back to client mode

                     

                    SW4-2590(config)#vtp mode client

                    Setting device to VTP CLIENT mode.

                     

                    SW4-2590(config)#do show vtp status

                    VTP Version                     : 2

                    Configuration Revision          : 14

                    Maximum VLANs supported locally : 250

                    Number of existing VLANs        : 6

                    VTP Operating Mode              : Client

                    VTP Domain Name                 : CISCO

                    VTP Pruning Mode                : Disabled

                    VTP V2 Mode                     : Disabled

                    VTP Traps Generation            : Disabled

                    MD5 digest                      : 0xF9 0x7D 0xCD 0x8B 0xE0 0x58 0x20 0x1E

                    Configuration last modified by 192.168.1.1 at 3-1-93 00:34:55

                     

                    We can conclude:

                    1. Changing to transparent mode decrements the configuration revision back to 0 but does not whipe out the original Vlans.

                     

                    2. Adding or deleting vlans in a transparent switch does not increment the configuration revision number, its stays at 0.

                     

                    3. Reverting back from transparent to client mode, whipes out your vlans and replaces them with the vlans in your VTP domain(obvious since all the switches in your domain will at this moment have higher revision number than 0)

                     

                    4. And lastly reverting back from transparent to client mode,  the configuration revision is reset to whichever configuration revision your VTP domain has at the moment( In our case it's 14)

                     

                    So changing from client to tranparent and then back to client is _not_ dangerous for your VTP domain, but it's dangerous for your local switch since all unique vlans created in  the transparent switch are going to be whiped out.

                     

                    HTH,

                     

                    Chemillio.