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Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 13 Configuring VLANs
Understanding VLANs
Figure 13-1 shows an example of VLANs segmented into logically defined networks.
Figure 13-1 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.
Traffic between VLANs must be routed or fallback bridged. The switch can route traffic between
VLANs by using switch virtual interfaces (SVIs). An SVI must be explicitly configured and assigned an
IP address to route traffic between VLANs. For more information, see the “Switch Virtual Interfaces”
section on page 11-5 and the “Configuring Layer 3 Interfaces” section on page 11-25.
Note If you plan to configure many VLANs on the switch and to not enable routing, you can use the sdm
prefer vlan global configuration command to set the Switch Database Management (sdm) feature to the
VLAN template, which configures system resources to support the maximum number of unicast MAC
addresses. For more information on the SDM templates, see Chapter 8, “Configuring SDM Templates,”
or see the sdm prefer command in the command reference for this release.
Supported VLANs
The switch supports VLANs in VTP client, server, and transparent modes. VLANs are identified by 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.
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