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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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Chapter 8 Configuring VLANs
Using 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 and that this trunk port is connected to the trunk port of a second switch.
Otherwise, the switch cannot receive any VTP advertisements.
VTP advertisements distribute this global domain information in VTP advertisements:
• VTP domain name
• VTP configuration revision number
• Update identity and update timestamp
• MD5 digest
VTP advertisements distribute this VLAN information for each configured VLAN:
• VLAN ID
• VLAN name
• VLAN type
• VLAN state
• Additional VLAN configuration information specific to the VLAN type
VTP Version 2
VTP version 2 supports these features not supported in version 1:
• Token Ring support—VTP version 2 supports Token Ring LAN switching and VLANs (Token Ring
Bridge Relay Function [TRBRF] and Token Ring Concentrator Relay Function [TRCRF]). For more
information about Token Ring VLANs, see the “VLANs in the VTP Database” section on page 8-20.
• 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
nonvolatile RAM 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. Because only one domain is supported, VTP version 2 forwards VTP messages in
transparent mode without checking the version and domain name.
• Consistency Checks—In VTP version 2, VLAN consistency checks (such as VLAN names and
values) are performed only when you enter new information through the CLI, the Cluster
Management software, or SNMP. Consistency checks are not performed when new information is
obtained from a VTP message or when information is read from nonvolatile RAM. If the digest on
a received VTP message is correct, its information is accepted without consistency checks.
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