the updater’s identity, the updater’s timestamp, and the MD5 digest field.
Subset advertisement—Contains very detailed information about the network, including the version,
code, sequence number, management domain name, configuration revision number, and VLAN
information fields.
•
VTP advertisements can contain the following information:
802.10 SAID values—For FDDI physical media.• Configuration revision number—The higher the number, the more updated the information.• Emulated LAN names—Used for ATM LANE.• Frame format—Information about the format and content of the frame.• Management domain name—The name of the VTP management domain. If the switch is configured
for one name and receives a frame with another name, the information is ignored.
•
MD5 digest—Used when a password is used throughout the domain. The key must match the key on
the given destination or the update information is ignored.
•
Updater identity—The identity of the switch that forwarded the summary advertisement to the switch.• VLAN configuration—Includes known VLAN information, specific parameters, and a maximum
transmission unit (MTU) size for each VLAN in the VTP management domain.
•
VLAN identification—The ISL or 802.1Q information.•
The advertisement frames are sent to a multicast address so all the VTP devices in the same management
domain can receive the frames. The frames are not forwarded using normal bridging controls. All VTP
management domain clients and servers update their databases on all deletions and additions on the network.
Therefore, only the VTP client operating in server mode needs to be updated with the deleted or additional
VLAN to allow all the members of the VTP management domain to update their databases.
There are two types of VTP management domain advertisements:
Server originating advertisements• Request advertisements from clients needing VLAN information upon power cycling or bootup•
Each advertisement has a revision number. The revision number is one of the most important parts of the VTP
advertisement. As a VTP database is modified, the VTP server increments the revision number by one. The
VTP server then advertises this information from its own database to other switches with the newly updated
revision number.
When VTP switches receive an advertisement that has a higher revision number, the switches will overwrite
the current database information stored in NVRAM with the new database information being advertised. If it
receives a lower revision number, the switch believes it has newer information and disregards the received
advertisement.
Can the VTP Revision Number on a New VTP Server Be a Problem?
When a new VTP revision number is sent throughout the VTP domain, the switches believe the highest
revision number has the most up−to−date information about all the VLANs. So, when switches detect the
additional VLANs within a VTP advertisement, they process the information received as authentic
information.
What happens when a new switch is configured as a server and the revision number is higher than the current
revision number used in the domain? Oops! If the rest of the domain gets that information, it reconfigures
every single member with the configuration on that new switch. This event could create a disaster on your
network. Unfortunately, any time a switch sees a higher revision number, it takes the information it just
received, considers it more current, and overwrites the existing database with the new configuration
information, even if this clears the VLAN information.
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