Cisco WS-C2950SX-48-SI Configuration Manual page 197

Chapter 9 Configuring VTP
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The VTP advertisement is regenerated on each of the device's trunk ports other than the trunk port on
which it was received.
Interaction with VTP Version 1 and VTP Version 2
VTP version 3 interacts with VTP version 1 and VTP version 2 switches as follows:
Note You should configure VTP version 1 and VTP version 2 switches as clients to allow them to work
properly with VTP version 3. See the
requirement.
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Limitations
The limitations of VTP version 3 are as follows:
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If the database revision number in the advertisement is freater than that of the receiving device, and
the advertisement's checksum and configuration information match, the receiving switch requests
the exact subset of databases for which it is not up to date.
A VTP version 3 switch is able to detect VTP version 1 and VTP version 2 switches and send a
scaled-down version of its database on a per-trunk basis in VTP version 2 format only. VTP
version 1 switches move to VTP version 2 mode without any configuration assistance.
A VTP version 3 switch never sends any VTP version 2 packets on a trunk unless it first receives a
legacy VTP version 1 or VTP version 2 packet on the trunk. This situation forces legacy neighboring
switches to keep advertising their presence on the link. If a VTP version 3 switch does not receive
a legacy packet on a trunk for a certain period of time, it is considered to be a VTP version 3-only
trunk and will not advertise a scaled-down version of the VLAN database on the trunk.
Even when advertising a VTP version 2 database on a trunk, VTP version 3 keeps sending VTP
version 3 updates through the port. This situation allows coexistence of two kinds of neighbors on
the trunk.
A VTP version 3 switch can modify reserved VLANs 1002–1005; however, these VLANs are set to
their default in the scaled-down database in VTP version 2 format.
A VTP version 3 switch never accepts a configuration from a VTP version 1 or VTP version 2
neighbor.
Two VTP version 3 regions can only communicate over a VTP version 1 and VTP version 2 region
in transparent mode.
Leaving a server in a VTP version 2 region so it will receive its VTP information from a VTP
version 3 region could be problematic. If there is a configuration change in the VTP version 1 and
VTP version 2 region, the revision of the database may become higher than the one that is generated
by the VTP version 3 region, and the updates from the VTP version 3 region would be ignored.
Note We recommend that you set all switches in the VTP version 1 and VTP version 2 region to
client and reset their revision number (do a reload or change the domain name back and
forth).
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
"Limitations" section on page 9-21
Understanding How VTP Version 3 Works
for an explanation of this
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Release 8.1
9-21