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16-2
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 16 Configuring VLANs
Understanding VLANs
Figure 16-1 shows an example of VLANs segmented into logically defined networks.
Figure 16-1 VLANs as Logically Defined Networks
VLANs are often associated with IP subnetworks. For example, all the end stations in a particular IP
subnet belong to the same VLAN. Interface VLAN membership on the switch is assigned manually on
an interface-by-interface basis. When you assign switch interfaces to VLANs by using this method, it is
known as interface-based, or static, VLAN membership.
Supported VLANs
Catalyst 2950 switches that run the standard software image (SI) support 128 VLANs; Catalyst 2950 and
Catalyst
2955 switches that run the enhanced software image (EI) For the list of switches that support
each image, see the release notes. VLANs are identified with a number from 1 to 4094. VLAN IDs 1002
through 1005 are reserved for Token Ring and FDDI VLANs. VTP only learns normal-range VLANs,
with VLAN IDs 1 to 1005; VLAN IDs greater than 1005 are extended-range VLANs and are not stored
in the VLAN database. The switch must be in VTP transparent mode when you create VLAN IDs from
1006 to 4094.
The switch supports per-VLAN spanning-tree plus (PVST+) with a maximum of spanning-tree
instances. One spanning-tree instance is allowed per VLAN. See the
“Normal-Range VLAN
Configuration Guidelines” section on page 16-5 for more information about the number of spanning-tree
instances and the number of VLANs. The switch supports IEEE 802.1Q trunking for sending VLAN
traffic over Ethernet ports.
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