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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter13 Configuring VLANs
Configuring Extended-Range VLANs
If the number of VLANs on the switch exceeds the maximum number of spanning-tree instances,
we recommend that you configure the IEEE 802.1s Multiple STP (MSTP) on your switch to map
multiple VLANs to a single spanning-tree instance. For more information about MSTP, see
Chapter 19, “Configuring MSTP.”
•Each routed port on the switch creates an internal VLAN for its use. These internal VLANs use
extended-range VLAN numbers, and the internal VLAN ID cannot be used for an extended-range
VLAN. If you try to create an extended-range VLAN with a VLAN ID that is already allocated as
an internal VLAN, an error message is generated, and the command is rejected.
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Because internal VLAN IDs are in the lower part of the extended range, we recommend that you
create extended-range VLANs beginning from the highest number (4094) and moving to the
lowest (1006) to reduce the possibility of using an internal VLAN ID.
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Before configuring extended-range VLANs, enter the show vlan internal usage privileged
EXEC command to see which VLANs have been allocated as internal VLANs.
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If necessary, you can shut down the routed port assigned to the internal VLAN, which frees up
the internal VLAN, and then create the extended-range VLAN and re-enable the port, which
then uses another VLAN as its internal VLAN. See the “Creating an Extended-Range VLAN
with an Internal VLAN ID” section on page13-13.
•Although the switch stack supports a total of 1005 (normal-range and extended-range) VLANs, the
number of routed ports, SVIs, and other configured features affects the use of the switch hardware.
If you try to create an extended-range VLAN and there are not enough hardware resources available,
an error message is generated, and the extended-range VLAN is rejected.
•In a switch stack, the whole stack uses the same running configuration and saved configuration, and
extended-range VLAN information is shared across the stack.
Creating an Extended-Range VLAN
You create an extended-range VLAN in global configuration mode by entering the vlan global
configuration command with a VLAN ID from 1006 to 4094. The extended-range VLAN has the default
Ethernet VLAN characteristics (see Table13-2) and the MTU size, private VLAN, and RSPAN
configuration are the only parameters you can change. See the description of the vlan global
configuration command in the command reference for the default settings of all parameters. In VTP
version 1 or 2, if you enter an extended-range VLAN ID when the switch is not in VTP transparent mode,
an error message is generated when you exit VLAN configuration mode, and the extended-range VLAN
is not created.
In VTP version 1 and 2, extended-range VLANs are not saved in the VLAN database; they are saved in
the switch running configuration file. You can save the extended-range VLAN configuration in the
switch startup configuration file by using the copy running-config startup-config privileged EXEC
command. VTP version 3 saves extended-range VLANs in the VLAN database.
Note Before you create an extended-range VLAN, you can verify that the VLAN ID is not used internally by
entering the show vlan internal usage privileged EXEC command. If the VLAN ID is used internally
and you want to free it up, go to the“Creating an Extended-Range VLAN with an Internal VLAN ID”
section on page 13-13 before creating the extended-range VLAN.