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Two different versions of VTP can run in
your management domain, VTP Version 1 and VTP Version 2. The two
versions are not interoperable. If you choose to configure a switch
in a domain for VTP Version 2, you must configure all switches in
the management domain to be in VTP Version 2. VTP Version 1 is the
default. You may need to implement VTP Version 2 if you need some of
the specific features that VTP Version 2 offers that are not offered
in VTP Version 1. The most common feature that is needed is Token
Ring VLAN support.
To configure the VTP version on a
Cisco IOS command-based switch, you must first enter VLAN database
mode. From there, you can set the VTP version as shown in Figure
.
In this example, VTP Version 2 has been configured.
Use the following command to change
the VTP version number on a set command-based switch. 
Switch (enable) set vtp v2
enable
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.
- 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 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 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 command-line interface (CLI) or Simple Network
Management Protocol (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. A switch that is capable of running VTP
Version 2 can operate in the same domain as a switch running VTP
Version 1 if VTP Version 2 remains disabled on the VTP Version
2-capable switch.
- If all switches in a domain are
capable of running VTP Version 2, you need to enable VTP Version
2 on only one switch (using the set
vtp v2 enable command).
The version number is propagated to the other VTP Version
2-capable switches in the VTP domain.
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