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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter1 Product Overview
Layer 3 Software Features

VLANs

A VLAN configures switches and routers according to logical, rath er than physical, topologies. Using
VLANs, a network administrator can combine any collection of LAN segments within an internetwork
into an autonomous user group, such that the segments appear as a single LAN in the network. VLANs
logically segment the network into different broadcast domains so that packets are switched only
between ports within the VLAN. Typically, a VLAN corresponds to a particular subnet, although not
necessarily.
For more information about VLANs, VTP, and Dynamic VLAN Membership, see Chapter10,
“Understanding and Configuring VLANs, VTP, andVMPS.”
The following VLAN-related features are also supported .
•VLAN Trunking Protocol (VTP)—VTP maintains VLAN naming consistency and con nectivity
between all devices in the VTP management domain. You can have redundancy in a domain by using
multiple VTP servers, through which you can maintain and modify the global VLAN information.
Only a few VTP servers are required in a large network.
•Private VLANs—Private VLANs are sets of ports that have the features of normal VLANs and also
provide some Layer 2 isolation from other ports on the switch.
For information about private VLANs, see Chapter 34, “Configuring Private VLANs.”
•Private VLAN Trunk Ports—Private VLAN trunk ports allow a secondary port on a private VLAN
to carry multiple secondary VLANs.
•Dynamic VLAN Membership—Dynamic VLAN Membership allows you to assi gn switch ports to
VLANs dynamically, based on the source Media Access Control (MAC) address of the device
connected to the port. When you move a host from a port on one switch in the network to a port on
another switch in the network, that switch dynamically assigns the new port to the proper VLAN for
that host. With the VMPS Client feature, you can convert a dynamic access port to a VMPS client.
VMPS clients can use VQP queries to communicate with the VMPS server to obtain a VLAN
assignment for the port based on the MAC address of the host attached to that port.
Layer 3 Software Features
A Layer 3 switch is a high-performance switch that has been optimized for a campus LAN or an intranet,
and it provides both wirespeed Ethernet routing and switching services. Layer 3 switching improves
network performance with two software functions—route processing and i ntelligent network services.
Compared to conventional software-based switches, Layer 3 switches process more packets faster; they
do so by using application-specific integrated circuit (ASIC) hardware instead of microprocess or-based
engines.
The following subsections describe the key Layer 3 switching software features on the Catalyst 4500
series switch:
•CEF, page 1-6
•HSRP, page 1-6
•IP Routing Protocols, page 1-6
•Multicast Services, page 1-8