9-16
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-03
Chapter9 Creating and Maintaining VLANs
VLANs in the VTP Database
VLAN Configuration Guidelines
Follow these guidelines when creating and modifying VLANs in yo ur ne two rk:
•The Catalyst 3550 switch supports 1005 VLANs in VTP client, server, and transp ar en t mo des.
VLANs are identified with a number between 1 and 1 001 . VLA N nu mb er s 10 02 thro ugh 10 05 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 forw ard
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 instance s 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 switc h (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 severa l
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 por t to tr unk , th e por t m ode i s not ch an ged.
•A port in dynamic mode can negotiate with its neighbor to become a trunk port. If yo u 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 por t m ode is not ch an ge d.
Table9-5 Ethernet VLAN Defaults and Ranges
Parameter Default Range
VLAN ID 1 1–1005
VLAN name default No range
802.10 SAID 1010 01 1–4294967294
MTU size 1500 1500–18190
Translational bridge 1 1002 0–1005
Translational bridge 2 1003 0–1005
VLAN state active active, suspend