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Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
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Chapter 8 Configuring VTP
Understanding How VTP Works
The following global configuration information is distributed in VTP advertisements:
• VLAN IDs (ISL and 802.1Q)
• Emulated LAN names (for ATM LANE)
• 802.10 SAID values (FDDI)
• VTP domain name
• VTP configuration revision number
• VLAN configuration, including maximum transmission unit (MTU) size for each VLAN
• Frame format
Understanding VTP Version 2
If you use VTP in your network, you must decide whether to use VTP version 1 or version 2.
Note If you are using VTP in a Token Ring environment, you must use version 2.
VTP version 2 supports the following 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 “Understanding How VLANs Work” section on
page 9-1.
• 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.
• Version-Dependent Transparent Mode—In VTP version 1, a VTP transparent network device
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 in the supervisor engine software,
VTP version 2 forwards VTP messages in transparent mode without checking the version.
• 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 digest on a received VTP message is correct, its
information is accepted without consistency checks.
Understanding VTP Pruning
VTP pruning enhances network bandwidth use by reducing unnecessary flooded traffic, such as
broadcast, multicast, unknown, and flooded unicast packets. VTP pruning increases available bandwidth
by restricting flooded traffic to those trunk links that the traffic must use to access the appropriate
network devices. By default, VTP pruning is disabled.
For VTP pruning to be effective, all devices in the management domain must support VTP pruning. On
devices that do not support VTP pruning, you must manually configure the VLANs allowed on trunks.
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