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Chapter17 Configuring VLANs
Understanding VLANs
Figure 17-1 shows an example of VLANs segmented into logically defined networks.
Figure17-1 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 swi tch is a ssigne d ma nua lly 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 VLA Ns. Refe r to t he
release notes for the list of switches that support each image. VLANs are identified with a number fr om
1 to 4094 when the EI is installed and 1 to 1005 when the SI is installed. VLAN ID s 1002 through 1005
are reserved for Token Ring and FDDI VLANs. VTP only learns norma l-range VLANs, with VLAN I Ds
1 to 1005; VLAN IDs greater than 1005 are extended-rang e V LAN s a nd a re n ot st ored i n the VLA N
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+) and rapid PVST+ 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 page17-5 for more information about the number of
spanning-tree instances and the number of VLANs. The switch suppo rt s IEE E 80 2.1 Q trun king fo r
sending VLAN traffic over Ethernet ports.
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