VLAN internal allocation policy ascending???

Unanswered Question
Nov 20th, 2008


Invented a really cool VLAN numbering scheme. However, on floors in buildings at 10th or higher it falls apart because the 6500s are set to assign its internal VLANs from 1006 up...runs in to our numbering scheme.

Want to change these allocations to DEscending down from 4094. What will happen to the already allocated 1006, 1007, 1008 internal VLANs already in use?

Do we have to reboot the box?

Many of these internal VLAN's are not on interfaces so we can't just shut no-shut interfaces to free them up.


I have this problem too.
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Giuseppe Larosa Thu, 11/20/2008 - 11:19

Hello Mike,

be aware that Vlans 1002,1003,1004,1005 are legacy Vlans for Token Ring and FDDI lan switching and cannot be used in modern ethernet only switches

I would suggest to adjust your Vlan numbering scheme accordingly.

Hope to help


mprescher Thu, 11/20/2008 - 11:21

Yep, thanks. Taking that in to account.

The real issue is, can the ascending be changed to descending without a reboot and if so, what will happen to already allocated internal VLAN's if we don't reboot?

I can lab it but if anybody has that knowledge it is another data point for us.

Jon Marshall Thu, 11/20/2008 - 11:22


Yes you would need to reboot the box.

But i'm not sure what you are trying to achieve. If you change to vlan internal policy descending then the 6500 will assign it's internal vlans from 4094 downwards so you could still get gaps in your vlan numbering scheme.


mprescher Thu, 11/20/2008 - 11:53

Ah, one of the things the number scheme relates to floors of a building so 10th floor is 10xx, 11th floor is 11xx. It so happens that where this is being applied there are no buildings taller than 11 floors and near zero likelihood there will be.

So, ascending parks internal VLANs at 1006 upward and gets in the way. Descending parks them from 4094 downward and wouldn't get in the way of the scheme.

So, my assumption from your response is, that the already allocated internal VLANs beginning at 1006 would NOT be re-assigned from 4094 on down with just the command change - a reboot is needed to make those already allocated internal VLANs, re-allocate themselves.

(We know that shut no shut for interface pre-allocated internal VLANs from the extended range will free up temporatily, making them available for use, (shut, grab your vlan and then no shut, go get a new different internal VLAN number) but many of the other internal VLAN allocations are not on interfaces and are for aspects that can not simply be toggled to force a re-allocation.)

Jon Marshall Thu, 11/20/2008 - 11:57


I would have to test to be absolutely sure but i know when i have changed it in the past the change does not take effect until a reboot of the switch.


mprescher Thu, 11/20/2008 - 12:29

Thanks, no worries. I can lab it. Anybody else used extended VLAN's and run in to this?


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