ccna wan

ccna wan.messages-if they come from the current VTP domain; however, these switches will decide whether to accept the changes indicated by the VTP messages based on a number of conditions. For example, one of the functions of VTP summary announcements is to ensure that all switches have the most up-to-date information. On a server switch, even if no changes are made during the 5-minute update interval, when this countdown timer expires, the server switch will still send a summary notice, but containing exactly the same information as the previous summary notice. It makes no sense to have the other switches then merge this information into the configuration, since they already have the most recent information.To make this process more efficient, a configuration revision number is used to keep track of which server has the most recent information. At first, this revision number is set to 0 If you perform a change on a server switch, it will add 1 to its own revision number, and over the trunk link will changecommunicated to the other switches. When the client switch or server switch receives these messages, it compares the revision number in the message with the revision number of the next message it receives. If the new message has a higher revision number, it means that the server switch must have made a change. If the VTP summary notice does not contain the necessary VLAN information, all client and server switches generate a notice request, and the server responds with a subnet notice that contains the details. Exam Point.The VTP monthly burst server generates a VTP multicast every 5 minutes. The revision number is configured to determine which server has the latest VLANinformation: the larger the revision number, the more recent the information. Don't forget that when connecting an existing server switch to a server/client VTP network, theThe server switch with the highest revision number will win and in turn use its VLAN information and remove the VLAN information from the other switches.If a server switch receives a VTP message from another server with a smaller revision number from the Notification Server, the receiving server will respond to the Notification Server using a VTP message containing its current configuration revision number. This tells the annunciation server that its VLAN information is not up to date and should be requested from the server that has the latest VLAN information. In this sense, the revision number in a VTP message is a bit like the sequence number used by TCP. Also, don't forget that transparent switches don't process these VTP announcements; they just passively forward these messages to other switches connected to their trunk ports.IOS switches store the VLAN database and revision numbers in the file vlan.dat rather than in the boot configuration file, and switches in server,transparent and client mode switches. The command to delete the startup configuration does not delete this file, so when you boot a switch whose revision number is higher than the revision number of an established server switch in the domain, the established VLAN information in the domain is overwritten by that switch's VLAN configuration information. Before connecting a switch to an existing network, its file vlan.dato should be deleted For this purpose, you can execute the command delete vlan.dato in privileged EXEC mode After executing this command, you must press the Enter key twice to confirm.12.3.3 VTP Pruning