Could you pls explain how can a new switch added as vtp client (with higher rev no.)erase vlan info.In some materials it says it can erase it,but some says it cant.Pls clarify
SW-11 will ignore the VTP updates from other switches because of their lower configuration revision number. At the same time, other switches will receive VTP updates from SW-11 ,finding that the received updates has a higher revison number and thus replace their own vlan info with the received updates. At that time, all switches will have identical vlan information as SW-11.
A typical wrong concept is that switches in VTP client mode cannot overcome switch in server mode. There is no such a definition about VTP client mode. The true definition of VTP client mode , according to "Cisco Lan Switch" by Kenndy Clark, page 545, is that switch in client mode CAN source and listen to VTP messages, but CANNOT create and remember VLAN. ("source" means send out VTP message, "remember" means store VLAN info on the NVRAM)
According to this definition, switches in server mode and client mode will both send out VTP messages, and there is no rule that messages from server mode should beat the one from client mode. The rule is the revision number determines who will win. However, it is rarely possible to make switch in client mode to have an higher revision number than one in server mode. I have designed a lab to make this happen, described as follows.
I have 3 swithces and have them connect as below:
SW1 and SW2 are VTP servers, while SW3 is a VTP client. The connections among them are trunks.
First I create 10 VLANs on SW1. All switches have 10 VLANs and VTP revision number 10.
Then I shutdown the connection between SW3 and SW2. SW2 is isolated from others, but VLAN info among them is still the same
Then I delete 5 VLAN on SW1. Now SW1 and SW3 have only 5 VLANs and VTP revision number 15. SW2 has 10 VLANs and VTP revision number 10.
Then I shutdown the connection between SW1 and SW3. Now we have 3 isolated switches. SW3 have 5 VLANs and VTP revision number 15. SW2 has 10 VLANs and VTP revision number 10.
Notice that SW3 is in VTP client mode and have an higher revision number than SW2 which is a VTP server. Now I restore the connection between SW3 and SW2 so they can start to exchange VTP message, and the result is -- Client prevails Server. HOORAY!
Option A commit a wrong concept and hope someone fall into the trap. Unfortunately , this happens all the time.