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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter10 Understanding and Configuring VLANs, VTP, andVMPS
VLAN Trunking Protocol
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 V TP version 1 or version 2.
Note Catalyst 4500 series switches do not support Token Ring or FDDI media. The switch does not forward
FDDI, FDDI-Net, Token Ring Concentrator Relay Function [TrCRF], or Token Ring Bridge Relay
Function [TrBRF] traffic, but it does propagate the VLAN configuration via VTP.
VTP version 2 supports the following features, which are not supported in version 1:
•Token Ring support—VTP version2 supports Token Ring LAN switching and VLANs (TrBRF and
TrCRF).
•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 support ed 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 f rom 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, and unicast packets. VTP pruning increases available ba ndwidth by restricting
flooded traffic to those trunk links that the traffic must use to access th e appropriate network devices.
By default, VTP pruning is disabled.
For VTP pruning to be effective, all devices in the management domain must either support VTP pruning
or, on devices that do not support VTP pruning, you must manually configure the VLA Ns allowed on
trunks.