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Catalyst 3750-X and 3560-X 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.
Traffic between VLANs must be routed or fallback bridged. The switch can route traffic between
VLANs by using switch virtual interfaces (SVIs).
Note Routing is not supported on switches running the LAN base feature set.
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 13-5 and the “Configuring Layer
3 Interfaces” section on page 13-37
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 version 1 and version 2 support only normal-range VLANs (VLAN IDs 1 to 1005). In these
versions, the switch must be in VTP transparent mode when you create VLAN IDs from 1006 to 4094.
VTP version 3 supports the entire VLAN range (VLANs 1 to 4094). Extended range VLANs (VLANs
1006 to 4094) are supported only in VTP version 3. You cannot convert from VTP version 3 to VTP
version 2 if extended VLANs are configured in the domain.
Although the switch or switch stack supports a total of 1005 (normal range and extended range) VLANs,
the number of routed ports, SVIs, and other configured features affects the use of the switch hardware.
90573
Switch A
Switch B
Trunk port 1
VLANs 2 – 4 (path cost 30)
VLANs 8 – 10 (path cost 19)
Trunk port 2
VLANs 8 – 10 (path cost 30)
VLANs 2 – 4 (path cost 19)