http://www.cisco.com/en/US/docs/ios/12_4t/12_4t15/ht_xvlan.html
That's it...
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Alessio
Update:
VLAN Trunking Protocol Guidelines
These are the guidelines for using extended VLAN ID with VLAN Trunking Protocol (VTP):
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Extended range VLANs are not controlled by VTP.
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VLANs in the extended range cannot be pruned. The VLAN range for the switchport trunk pruning vlan command remains 1-1005.
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The VTP supported VLAN configuration (VLANs 1-1005) is included in the Cisco IOS configuration file only when the device is in VTP transparent mode.
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VTP learns only normal-range VLANs, with VLAN IDs 1 to 1005; extended-range VLANs are not stored in the VLAN database. The router must be in VTP transparent mode when you create extended-range VLANs.