Cisco Systems 4500 About VTP

13-8
Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 13 Configuring VLANs, VTP, and VMPS
VLAN Trunking Protocol
About VTP
VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the
addition, deletion, and renaming of VLANs within a VTP domain. A VTP domain (also called a VLAN
management domain) is made up of one or more network devices that share the same VTP domain name
and that are interconnected with trunks. VTP minimizes misconfigurations and configuration
inconsistencies that can result in a number of problems, such as duplicate VLAN names, incorrect
VLAN-type specifications, and security violations.
Before you create VLANs, you must decide whether you want to use VTP in your network. With VTP,
you can make configuration changes centrally on one or more network devices and have those changes
automatically communicated to all the other network devices in the network. For details on configuring
VLANs, see the “VLANs” section on page 13-1
These sections describe how VTP works:
• Understanding the VTP Domain, page 13-8
• Understanding VTP Modes, page 13-9
• Understanding VTP Advertisements, page 13-9
• Understanding VTP Versions, page 13-9
• Understanding VTP Pruning, page 13-11
Understanding the VTP Domain
A VTP domain is made up of one or more interconnected network devices that share the same VTP
domain name. A network device can be configured to be in only one VTP domain. You make global
VLAN configuration changes for the domain using either the command-line interface (CLI) or Simple
Network Management Protocol (SNMP).
By default, the Catalyst 4500 series switch is in VTP server mode and the domain is set to NULL until
the switch receives an advertisement for a domain over a trunk link or you configure a management
domain. You cannot create or modify VLANs on a VTP server until the management domain name is
specified or learned.
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 ignores advertisements with a different
management domain name or an earlier configuration revision number.
If you configure the switch as VTP transparent, you can create and modify VLANs, but the changes
affect only the individual switch.
When you make a change to the VLAN configuration on a VTP server, the change is propagated to all
network devices in the VTP domain. VTP advertisements are transmitted out all Inter-Switch Link (ISL)
and IEEE 802.1Q trunk connections.
VTP maps VLANs dynamically across multiple LAN types with unique names and internal index
associations. Mapping eliminates unnecessary device administration for network administrators.