Chapter 10 Understanding And Configuring Vlans; Overview Of Vlans - Cisco 4500M Software Manual

Understanding and Configuring VLANs
This chapter describes VLANs on Catalyst 4500 series switches. It also provides guidelines, procedures,
and configuration examples.
This chapter includes the following major sections:
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For complete syntax and usage information for the switch commands used in this chapter, refer to the
Note
Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm.

Overview of VLANs

A VLAN is a group of devices on one or more LANs that are configured to communicate as if they were
attached to the same wire, when in fact they are located on a number of different LAN segments. Because
VLANs are based on logical instead of physical connections, they are extremely flexible.
VLANs define broadcast domains in a Layer 2 network. A broadcast domain is the set of all devices that
will receive broadcast frames originating from any device within the set. Broadcast domains are typically
bounded by routers because routers do not forward broadcast frames. Layer 2 switches create broadcast
domains based on the configuration of the switch. Switches are multiport bridges that allow you to create
multiple broadcast domains. Each broadcast domain is like a distinct virtual bridge within a switch.
You can define one or many virtual bridges within a switch. Each virtual bridge you create in the switch
defines a new broadcast domain (VLAN). Traffic cannot pass directly to another VLAN (between
broadcast domains) within the switch or between two switches. To interconnect two different VLANs,
you must use routers or Layer 3 switches. See the
for information on inter-VLAN routing on Catalyst 4500 series switches.
Figure 10-1
OL-6696-01
Overview of VLANs, page 10-1
VLAN Configuration Guidelines and Restrictions, page 10-3
VLAN Default Configuration, page 10-4
Configuring VLANs, page 10-4
shows an example of three VLANs that create logically defined networks.
C H A P T E R
"Overview of Layer 3 Interfaces" section on page 23-1
Software Configuration Guide—Release 12.2(25)EW
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10-1