Chapter 12 Configuring Vlan - Cisco Catalyst 3550 series Software Configuration Manual

Understanding VLANs
Figure 12-1
Figure 12-1 VLANs as Logically Defined Networks
Cisco router
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. A Catalyst 3550 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
Interfaces" section on page 10-4
Supported VLANs
The Catalyst 3550 switch supports 1005 VLANs in VTP client, server, and transparent modes. 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+) and rapid PVST+ with a maximum of 128
spanning-tree instances. One spanning-tree instance is allowed per VLAN. See the
VLAN Configuration Guidelines" section on page 12-5
spanning-tree instances and the number of VLANs. The switch supports both Inter-Switch Link (ISL)
and IEEE 802.1Q trunking methods for sending VLAN traffic over Ethernet ports.
Catalyst 3550 Multilayer Switch Software Configuration Guide
12-2
shows an example of VLANs segmented into logically defined networks.
Fast
Ethernet
Engineering Marketing
VLAN VLAN
and the "Configuring Layer 3 Interfaces" section on page
for more information about the number of
Chapter 12 Configuring VLANs
Accounting
VLAN
Floor 3
Floor 2
Floor 1
"Switch Virtual
10-18.
"Normal-Range
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