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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 9 Creating and Maintaining VLANs
VLANs in the VTP Database
VLAN Configuration Guidelines
Follow these guidelines when creating and modifying VLANs in your network:
•
The Catalyst 3550 switch supports 1005 VLANs in VTP client, server, and transparent modes.
VLANs are identified with a number between 1 and 1001. VLAN numbers 1002 through 1005 are
reserved for Token Ring and FDDI VLANs.
•
Before you can create a VLAN, the switch must be in VTP server mode or VTP transparent mode.
If the switch is a VTP server, you must define a VTP domain.
•
Catalyst 3550 switches do not support Token Ring or FDDI media. The switch does not forward
FDDI, FDDI-Net, TrCRF, or TrBRF traffic, but it does propagate the VLAN configuration
through VTP.
•
The switch supports 128 spanning-tree instances. If a switch has more active VLANs than supported
spanning-tree instances, STP 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 anywhere in the VTP domain 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 all have run out of spanning-tree instances. You can prevent this possibility
by setting allowed lists on the trunk ports of switches that have used up their allocation of
spanning-tree instances.
•
If you try to enable 802.1X on a trunk port, an error message appears, and 802.1X is not enabled. If
you try to change the mode of an 802.1X-enabled port to trunk, the port mode is not changed.
•
A port in dynamic mode can negotiate with its neighbor to become a trunk port. If you try to enable
802.1X on a dynamic port, an error message appears, and 802.1X is not enabled. If you try to change
the mode of an 802.1X-enabled port to dynamic, the port mode is not changed.
Table 9-5
Ethernet VLAN Defaults and Ranges
Parameter
Default
Range
VLAN ID
1
1–1005
VLAN name
default
No range
802.10 SAID
101001
1–4294967294
MTU size
1500
1500–18190
Translational bridge 1
1002
0–1005
Translational bridge 2
1003
0–1005
VLAN state
active
active, suspend