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CHAPTER
9-1
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-03
9
Creating and Maintaining VLANs
This chapter describes how to create and maintain VLANs. It includes information about VLAN modes,
the VLAN Trunking Protocol (VTP) database, and the VLAN Membership Policy Server (VMPS).
Note For complete syntax and usage information for the commands used in this chapter, refer to the
Catalyst 3550 Multilayer Switch Command Reference for this release.
The chapter includes these sections:
• Understanding VLANs, page 9-1
• Using the VLAN Trunking Protocol, page 9-3
• VLANs in the VTP Database, page 9-15
• Understanding VLAN Trunks, page 9-22
• Understanding VMPS, page 9-33
Understanding VLANs
A VLAN is a switched network that is logically segmented by function, project team, or application,
without regard to the physical locations of the users. VLANs have the same attributes as physical LANs,
but you can group end stations even if they are not physically located on the same LAN segment. Any
switch port can belong to a VLAN, and unicast, broadcast, and multicast packets are forwarded and
flooded only to end stations in the VLAN. Each VLAN is considered a logical network, and packets
destined for stations that do not belong to the VLAN must be forwarded through a router or bridge as
shown in Figure 9-1. Because a VLAN is considered a separate logical network, it contains its own
bridge Management Information Base (MIB) information and can support its own implementation of the
Spanning Tree Protocol (STP).
Note Before you create VLANs, you must decide whether to use VTP to maintain global VLAN
configuration for your network. For more information on VTP, see the “Using the VLAN Trunking
Protocol” section on page 9-3.
Figure 9-1 shows an example of VLANs segmented into logically defined networks.