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Catalyst 3750 Switch Software Configuration Guide
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Chapter 14 Configuring VTP
Understanding VTP
The switch supports 1005 VLANs, but the number of routed ports, SVIs, and other configured features
affects the usage of the switch hardware. If the switch is notified by VTP of a new VLAN and the switch
is already using the maximum available hardware resources, it sends a message that there are not enough
hardware resources available and shuts down the VLAN. The output of the show vlan user EXEC
command shows the VLAN in a suspended state.
VTP only learns about normal-range VLANs (VLAN IDs 1 to 1005). Extended-range VLANs (VLAN
IDs greater than 1005) are not supported by VTP or stored in the VTP VLAN database.
This section contains information about these VTP parameters and characteristics.
• The VTP Domain, page 14-2
• VTP Modes, page 14-3
• VTP Advertisements, page 14-3
• VTP Version 2, page 14-4
• VTP Pruning, page 14-5
• VTP and Switch Stacks, page 14-6
The VTP Domain
A VTP domain (also called a VLAN management domain) consists of one switch or several
interconnected switches or switch stacks 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 14-15 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 trunk connections, including
Inter-Switch Link (ISL) and IEEE 802.1Q. VTP dynamically maps VLANs with unique names and
internal index associates across multiple LAN types. Mapping eliminates excessive device
administration required from network administrators.
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