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New Member

VLAN Configuration Revision Number

Does cisco switch in client mode uses VLAN configuration Revision Number? If yes when does the config revision number changes?

I am asking this because I have found specific warning about introducing a new switch in the existing envoronmnet as given below.

Be aware that if a new switch is attached to an existing VTP domain and the new switch has the same VTP domain and has a VLAN database configuration revision that is higher than that which is currently present in the existing network, the existing VLAN database is overwritten with the VLAN database on the new switch, regardless of whether the switch is a VTP server or client. Yes, that's right; even if the switch is a VTP client, if it has the same VTP domain name and a higher VLAN database configuration revision number, the existing VLAN database is overwritten.

Thanks

8 REPLIES

Re: VLAN Configuration Revision Number

Yes, it does exactly what is stated above.

You should beware that the config-rev on the live network is a number that is sufficiently high to prevent accidental erasing of the vlan configuration. You can increase the config rev simply by adding a fake vlan and exit the config, subsequently re-enter and erase the fake vlan again. This will increase the config rev each time you exit the vlan database. Making multiple changes in one step accounts for an increase by only one.

Altering the vtp domain name also resets the config rev. so make sure that this is the last thing that you change, exit config mode and reload the switch.

Regards,

Leo

Blue

Re: VLAN Configuration Revision Number

YES,

VTP client does use the VLAN config. revision number.

every VTP advertisement contains the VLAN config. revision number, as well as other info.

the VLAN config. revision number tells VTP receiver whether or not it is to ignore the VTP advertisement.

if the VLAN config. revision number in a VTP advertisement is less than that of the receivers currently running VLAN config. revision number, then the VTP advertisement would be ignored and the switch would not inherit the Rev.#.

(if the Rev.# was higher than the receivers, it would tell that receiver VTP to update its information with the new 'higher' version)

please see this link for more info on the VTP VLAN config. revision number:

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_guide_chapter09186a0080160a7d.html#wp1020394

in order to see the VLAN configuration revision number perform the following:

IOS switch -

switch# show vtp status

CatOS switch -

switch>(enable) show vtp domain

New Member

Re: VLAN Configuration Revision Number

Thank you for the update. Since vlans cannot be created/deleted on the switch which is in the client mode, when does vlan configuration revision number changes on the switch which is in the client mode?

Thanks

Re: VLAN Configuration Revision Number

you are right that vlans cant be created and deleted in client mode. VLANs can be created in server mode.

VTP (VLAN Trunking protocol) is a layer 2 protocol used for maintaing consistent VLAN information in all switches in a VTP domain.

whenever vlan is created on switch in server mode, its configuration revsion is incremented by 1 and this infor is propogated to all switches in that VTP domain using VTP.

when switch in client mode receive the information, it checks its configuraion revision number with the one it has received.

if it already has higher revision number, then it discards that packet else it synchronize its vlan database with the one it has received.

in your case you have added a switch which has config revision number higher than the exisitng one in ur network. in this case vlan.dat file in ur exisitng switches which has vlan info will be replaced by the vlan.dat file in the new switch which sometimes can be dangerous and ur entire network can go for a toss.

so it is always recommendable to set the config revision number of ur new switch to 0 or set the vtp mode to transparent before adding the new switch in the live network.

hope this information helps ...

sourabh

New Member

Re: VLAN Configuration Revision Number

helpful information..

Purple

Re: VLAN Configuration Revision Number

Some people seem concerned about this , if you remember 1 thing before configuring just wipe out the old config and you will never have to worry about a client switch wiping out the config . If you do this then enter the vtp domain name it starts at revision number 1 and won't be higher than your network...

New Member

Re: VLAN Configuration Revision Number

when ever adding new switch into VTP domain first change the VTp MODE into transparent then put into client ,this is best way to set revision 0.

New Member

Re: VLAN Configuration Revision Number

Before I add a switch to our network, that is the first thing I look at. Also, please correct me if I'm wrong, If you enable the password to the VTP server, this might prevent it from accidentally deleting your VLAN Database.

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