Extended Range VLAN - FAIL

I was reading an old post on CCIE talk about extended range vlans and I learned something new. The post is here: CCIE Talk

If a Catalyst switch has any routed ports then it uses an extended vlan as an "internal vlan" for that port. Why? I don't know but it's something to take caution with if you run into any issues.

Check it out:

SW1#sho vlan internal usage

VLAN Usage
---- --------------------

Now let's create a routed port:

SW1(config)#int f0/24
SW1(config-if)#no sw

Now we have VLAN 1006 taken up:

SW1#sho vlan internal usage

VLAN Usage
---- --------------------
1006 FastEthernet0/24

SW1#

What happens if we try to create or modify VLAN 1006? Let's see:

SW1(config)#vlan 1006
SW1(config-vlan)#exit
% Failed to create VLANs 1006
VLAN(s) not available in Port Manager.
%Failed to commit extended VLAN(s) changes.
00:06:13: %PM-4-EXT_VLAN_INUSE: VLAN 1006 currently in use by FastEthernet0/24
00:06:13: %SW_VLAN-4-VLAN_CREATE_FAIL: Failed to create VLANs 1006: VLAN(s) not available in Port Manager
SW1(config)#

FAIL. What if we were supposed to use VLAN 1006? Shut it down, enable VLAN 1006, then re-enable the port.

SW1(config)#int f0/24
SW1(config-if)#shut
SW1(config)#do show vlan internal usa

VLAN Usage
---- --------------------

SW1(config)#vlan 1006
SW1(config-vlan)#exit
SW1(config)#int f0/24
SW1(config-if)#no shut
SW1(config-if)#exit
SW1(config)#do show vlan internal usa

VLAN Usage
---- --------------------
1007 FastEthernet0/24

The switch uses the next number.