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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 16 Configuring VTP
Understanding VTP
VTP Advertisements
Each switch in the VTP domain sends periodic global configuration advertisements from each trunk port
to a reserved multicast address. Neighboring switches receive these advertisements and update their VTP
and VLAN configurations as necessary.
Note Because trunk ports send and receive VTP advertisements, you must ensure that at least one trunk port
is configured on the switch or switch stack and that this trunk port is connected to the trunk port of
another switch. Otherwise, the switch cannot receive any VTP advertisements. For more information on
trunk ports, see the “Configuring VLAN Trunks” section on page 15-14.
VTP advertisements distribute this global domain information:
• VTP domain name
• VTP configuration revision number
• Update identity and update timestamp
• MD5 digest VLAN configuration, including maximum transmission unit (MTU) size for each
VLAN.
• Frame format
VTP advertisements distribute this VLAN information for each configured VLAN:
• VLAN IDs (ISL and IEEE 802.1Q)
• VLAN name
• VLAN type
• VLAN state
• Additional VLAN configuration information specific to the VLAN type
In VTP version 3, VTP advertisements also include the primary server ID, an instance number, and a
start index.
VTP Version 2
If you use VTP in your network, you must decide which version of VTP to use. By default, VTP operates
in version 1.
VTP version 2 supports these features that are not supported in version 1:
• Token Ring support—VTP version 2 supports Token Ring Bridge Relay Function (TrBRF) and
Token Ring Concentrator Relay Function (TrCRF) VLANs. For more information about Token Ring
VLANs, see the “Configuring Normal-Range VLANs” section on page 15-4.
• Unrecognized Type-Length-Value (TLV) support—A VTP server or client propagates configuration
changes to its other trunks, even for TLVs it is not able to parse. The unrecognized TLV is saved in
NVRAM when the switch is operating in VTP server mode.
• Version-Dependent Transparent Mode—In VTP version 1, a VTP transparent switch inspects VTP
messages for the domain name and version and forwards a message only if the version and domain
name match. Although VTP version 2 supports only one domain, a VTP version 2 transparent switch
forwards a message only when the domain name matches.