Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR
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Chapter 7 Configuring VLANs
Creating and Modifying VLANs
VLAN Configuration Guidelines
Follow these guidelines when creating and modifying VLANs in your network:
• The router supports 1005 VLANs.
• Normal-range Ethernet VLANs are identified with a number between 1 and 1001. VLAN numbers
1002 through 1005 are reserved for Token Ring and FDDI VLANs.
• The router does not support Token Ring or FDDI media. The switch does not forward FDDI,
FDDI-Net, TrCRF, or TrBRF traffic.
• VLAN configurations for VLANs 1 to 1005 are always saved in the VLAN database and in the
switch running configuration file.
• Configuration options for VLAN IDs 1006 through 4094 (extended-range VLANs) are limited to
MTU. Extended-range VLANs are not saved in the VLAN database.
• STP is enabled by default only for NNIs on all VLANs. You can configure STP on ENIs. NNIs and
ENIs in the same VLAN are in the same spanning-tree instance. The switch supports 128
spanning-tree instances. If a switch has more active VLANs than supported spanning-tree instances,
spanning tree can be enabled on 128 VLANs and is disabled on the remaining VLANs. If you have
already used all available spanning-tree instances on a switch, adding another VLAN creates a
VLAN on that switch that is not running spanning tree. If you have the default allowed list on the
trunk ports of that switch (which is to allow all VLANs), the new VLAN is carried on all trunk ports.
Depending on the topology of the network, this could create a loop in the new VLAN that would not
be broken, particularly if there are several adjacent switches that have run out of spanning-tree
instances. You can prevent this by setting allowed lists on the trunk ports of switches that have used
up their allocation of spanning-tree instances.
If the number of VLANs on the switch exceeds the number of supported spanning-tree instances,
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 10, “Configuring MSTP.”
Note MSTP is supported only on NNIs on ENIs on which STP has been enabled.
• 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.
– 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.
– Before configuring extended-range VLANs, enter the show vlan internal usage privileged
EXEC command to see which VLANs have been allocated as internal VLANs.
VLAN state active active, suspend
UNI-ENI VLAN UNI-ENI isolated VLAN 2–1001, 1006–4094
VLAN 1 is always a UNI-ENI isolated
VLAN.
Table 7-2 Ethernet VLAN Defaults and Ranges (continued)
Parameter Default Range