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15-2
Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 15 Configuring VTP
Understanding VTP
The VTP Domain
A VTP domain (also called a VLAN management domain) consists of one switch or several
interconnected switches under the same administrative responsibility sharing the same VTP domain
name. A switch can be in only one VTP domain.You make global VLAN configuration changes for the
domain by using the command-line interface (CLI), Cluster Management Suite (CMS) software, or
Simple Network Management Protocol (SNMP).
By default, the switch is in VTP no-management-domain state until it receives an advertisement for a
domain over a trunk link (a link that carries the traffic of multiple VLANs) or until you configure a
domain name. Until the management domain name is specified or learned, you cannot create or modify
VLANs on a VTP server, and VLAN information is not propagated over the network.
If the switch receives a VTP advertisement over a trunk link, it inherits the management domain name
and the VTP configuration revision number. The switch then ignores advertisements with a different
domain name or an earlier configuration revision number.
Caution Before adding a VTP client switch to a VTP domain, always verify that its VTP configuration revision
number is lower than the configuration revision number of the other switches in the VTP domain.
Switches in a VTP domain always use the VLAN configuration of the switch with the highest VTP
configuration revision number. If you add a switch that has a revision number higher than the revision
number in the VTP domain, it can erase all VLAN information from the VTP server and VTP domain.
See the “Adding a VTP Client Switch to a VTP Domain” section on page 15-15 for the procedure for
verifying and resetting the VTP configuration revision number.
When you make a change to the VLAN configuration on a VTP server, the change is propagated to all
switches in the VTP domain. VTP advertisements are sent over all IEEE 802.1Q trunk connections. VTP
maps VLANs dynamically across multiple LAN types with unique names and internal index associates.
Mapping eliminates excessive device administration required from network administrators.
If you configure a switch for VTP transparent mode, you can create and modify VLANs, but the changes
are not sent to other switches in the domain, and they affect only the individual switch. However,
configuration changes made when the switch is in this mode are saved in the switch running
configuration and can be saved to the switch startup configuration file.
For domain name and password configuration guidelines, see the “VTP Configuration Guidelines”
section on page 15-8.