Cisco Systems 3750E manual VTP Version, VTP Pruning, 14-4

Chapter 14 Configuring VTP

Understanding VTP

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

VTP Version 2

If you use VTP in your network, you must decide whether to use Version 1 or Version 2. 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 13-4.

•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. Because VTP Version 2 supports only one domain, it forwards VTP messages in transparent mode without inspecting 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 or SNMP. Consistency checks are not performed when new information is obtained from a VTP message or when information is read from NVRAM. If the MD5 digest on a received VTP message is correct, its information is accepted.

VTP Pruning

VTP pruning increases network available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to reach the destination devices. Without VTP pruning, a switch floods broadcast, multicast, and unknown unicast traffic across all trunk links within a VTP domain even though receiving switches might discard them. VTP pruning is disabled by default.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

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