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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 18 Configuring VTP
Information About Configuring VTP
When a VTP version 3 device detects a VTP version 2 device on a trunk port, it continues to send
VTP version 3 packets, in addition to VTP version 2 packets, to allow both kinds of neighbors to
coexist on the same trunk.
A VTP version 3 device does not accept configuration information from a VTP version 2 or version
1 device.
Two VTP version 3 regions can only communicate in transparent mode over a VTP version 1 or
version 2 region.
Devices that are only VTP version 1 capable cannot interoperate with VTP version 3 devices.
VTP version 2 and version 3 are disabled by default.
When you enable VTP version 2 on a switch, every VTP version 2-capable switch in the VTP
domain enables version 2. To enable VTP version 3, you must manually configure it on each switch.
With VTP versions 1 and 2, you can configure the version only on switches in VTP ser ver or
transparent mode. If a switch is running VTP version 3, you can change to version 2 when the switch
is in client mode if no extended VLANs exist, no private VLANs exist, and no hidden pass word was
configured.
Caution In VTP version 3, both the primary and secondary servers can exist on an instance in the domain.
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.
VTP pruning blocks unneeded flooded traffic to VLANs on trunk ports that are included in the
pruning-eligible list. Only VLANs included in the pruning-eligible list can be pruned. By default,
VLANs 2 through 1001 are pruning eligible switch trunk por ts. If the VLANs are configured as
pruning-ineligible, the flooding continues. VTP pruning is supported in all VTP versions.
Figure 18-1 shows a switched network without VTP pruning enabled. Port 1 on Switch A and Port 2 on
Switch D are assigned to the Red VLAN. If a broadcast is sent from the host connected to Switch A,
Switch A floods the broadcast and every switch in the network receives it, even though Switches C, E,
and F have no ports in the Red VLAN.