10-18
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 10 Configuring VTP
Understanding How VTP Version 3 Works
Switches running VTP version 3 have the following common characteristics:
•
They accept only VTP packets from the same VTP domain.
•
If they do not have a primary server, they accept the primary server that is associated with the first
VTP database that they receive for any instance.
•
They accept only a database with a higher revision number from their current primary server.
•
If they have a password configured (whether hidden or not hidden), they accept only a new database
or a takeover message if it contains the correct password.
VTP version 3 modes are described in the following sections:
•
Client Mode, page 10-18
•
Server Mode, page 10-18
•
Transparent and VTP Off Modes, page 10-19
For more information on configuring modes, see the
“Changing VTP Version 3 Modes” section on
page 10-23
.
Client Mode
VTP version 3 clients are similar to VTP version 1 and VTP version 2 clients as follows:
•
A VTP client accepts a VTP configuration from the network but cannot generate or alter the
configuration.
•
A VTP client stores the VTP configuration that it receives in RAM (not NVRAM). When a VTP
client boots, it needs to reacquire the entire configuration that is propagated by VTP, including the
identity of the primary server.
•
A VTP client that cannot store the entire VTP configuration that is received in an instance to RAM,
immediately transitions to transparent mode.
Server Mode
Primary and secondary servers are two types of servers that may exist on a VLAN or VTP instance in
the VTP domain.
Secondary Server
When a switch is configured to be a server, it becomes a secondary server by default. As a secondary
server, a VTP version 3 switch behaves as a client with the following exceptions:
•
A secondary server immediately stores the information that is received through VTP version 3 in
NVRAM. This NVRAM is part of the running configuration or startup configuration.
•
At startup, a secondary server that has a configuration in NVRAM starts advertising the
configuration. The main purpose of a VTP secondary server is to back up the configuration that is
propagated over the network.
•
Similar to a client, a VTP secondary server cannot modify the VTP configuration.
•
A VTP server reverts to client mode if it cannot store the configuration in NVRAM.
•
A VTP version 3 secondary server can issue a takeover to become a primary server.