Specifications

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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 15 Configuring VLANs
Understanding VLANs
Figure 15-1 shows an example of VLANs segmented into logically defined networks.
Figure 15-1 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 64 VLANs; Catalyst 2950 and
Catalyst 2955 switches that run the enhanced software image (EI) support 250 VLANs. Refer to the
release notes for the list of switches that support each image. VLANs are identified with a number from
1 to 4094 when the EI is installed and 1 to 1005 when the SI is installed. 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 (PVST) and per-VLAN rapid spanning tree (PVRST) with
a maximum of 64 spanning-tree instances. One spanning-tree instance is allowed per VLAN. See the
“Normal-Range VLAN Configuration Guidelines” section on page 15-5 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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