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There is a feature on Cat 4000, 5000 and 6000 series switches :

VTP pruning cannot be applied to VLANs that need to exist everywhere and to be allowed on all switches in the campus (to be able to carry VTP, CDP traffic, and other control traffic). There is a way, however, to limit the extent of VLAN 1. This is a feature called VLAN 1 disable on trunk, and it is available on Catalyst 4000, 5000, and 6000 family switches since Cisco IOS release 5.4(x). This allow you to prune VLAN 1 from a trunk as you would do for any other VLAN, but this pruning will not include all of the control protocol traffic that will still be allowed on the trunk (DTP, PagP, CDP, VTP, and so on). However, you will block all user traffic on that trunk. Using this feature, you can completely avoid the VLAN spanning the entire campus, and as such, STP loops will be limited in extent, even in VLAN 1. You can configure VLAN 1 to be disabled as you would configure other VLANs to be cleared from the trunk by issuing the following commands:

Console> (enable) set trunk 2/1 Des

Port(s) 2/1 trunk mode set to desirable.

Console> (enable) clear trunk 2/1 1

Removing Vlan(s) 1 from allowed list.

Port 2/1 allowed vlans modified to 2-1005.

Is the feature also supported on Cat 3550. On 3550 I can clear vlan 1 from the trunk. Does it also means that now vlan 1 is prune eligible ?


Cisco Employee

Re: Vlan

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