[-] VTPv1 and VTPv2 use four types of messages:
■ Summary Advertisement: This message is originated by VTP Server and Client switches every 5 minutes and, in addition, after each modification to the VLAN database. This message carries information about VTP domain name, revision number, identity of the last updater, time stamp of the last update, MD5 sum computed over the contents of the VLAN database and the
VTP password (if configured), and the number of Subset Advertisement messages that optionally follow this Summary Advertisement. Summary Advertisement messages do not carry VLAN database contents.
■ Subset Advertisement: This message is originated by VTP Server and Client switches after modifying the VLAN database. Subset Advertisements carry full contents of the VLAN database. One Subset Advertisement can hold multiple VLAN database entries. However, multiple Subset Advertisements might be required if the VLAN database is large.
■ Advertisement Request: This message is originated by VTP Server and Client switches to request their neighbors send the complete VLAN database or a part of it. Advertisement requests are sent when a VTP Client switch is restarted, when a switch enters the Client mode, or when a Server or Client switch receives a Summary Advertisement with a higher revision
number than its own.
■ Join: This message is originated by each VTP Server and Client switch periodically every 6 seconds if VTP Pruning is active. Join messages contain a bit field that, for each VLAN in the normal range, indicates whether it is active or unused (that is, pruned).
Note In any VTP version, VTP messages are transmitted and accepted only on trunk ports. Access ports neither send nor accept VTP messages. For two switches to communicate in VTP, they must first be interconnected through a working trunk link.
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