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16-6
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 16 Configuring VLANs
Configuring Normal-Range VLANs
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 the number of VLANs on the switch exceeds the number of supported 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 STP instance. For more information about MSTP, see
Chapter 14,
“Configuring MSTP.”
VLAN Configuration Mode Options
You can configure normal-range VLANs (with VLAN IDs 1 to 1005) by using these two configuration
modes:
• VLAN Configuration in config-vlan Mode, page 16-6
You access config-vlan mode by entering the vlan vlan-id global configuration command.
• VLAN Configuration in VLAN Configuration Mode, page 16-6
You access VLAN database configuration mode by entering the vlan database privileged EXEC
command.
VLAN Configuration in config-vlan Mode
To access config-vlan mode, enter the vlan global configuration command with a VLAN ID. Enter a new
VLAN ID to create a VLAN or with an existing VLAN ID to modify the VLAN. You can use the default
VLAN configuration (
Table 16-2) or enter multiple commands to configure the VLAN. For more
information about commands available in this mode, see the vlan global configuration command
description in the command reference for this release. When you have finished the configuration, you
must exit config-vlan mode for the configuration to take effect. To display the VLAN configuration,
enter the show vlan privileged EXEC command.
You must use this config-vlan mode when creating extended-range VLANs (VLAN IDs greater than
1005). See the
“Configuring Extended-Range VLANs” section on page 16-11.
VLAN Configuration in VLAN Configuration Mode
To access VLAN configuration mode, enter the vlan database privileged EXEC command. Then enter
the vlan command with a new VLAN ID to create a VLAN or with an existing VLAN ID to modify the
VLAN. You can use the default VLAN configuration (
Table 16-2) or enter multiple commands to
configure the VLAN. For more information about keywords available in this mode, see the vlan VLAN
configuration command description in the command reference for this release. When you have finished
the configuration, you must enter apply or exit for the configuration to take effect. When you enter the
exit command, it applies all commands and updates the VLAN database. VTP messages are sent to other
switches in the VTP domain, and the privileged EXEC mode prompt appears.
Saving VLAN Configuration
The configurations of VLAN IDs 1 to 1005 are always saved in the VLAN database (vlan.dat file). If
VTP mode is transparent, they are also saved in the switch running configuration file, and you can enter
the copy running-config startup-config privileged EXEC command to save the configuration in the