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Configuring InterVLAN Routing with Catalyst 3750/3560/3550 Series Switches
Document ID: 41260
Introduction Prerequisites Requirements Components Used Related Products Conventions Background Theory Configure Network Diagram Configurations Verify Troubleshoot Troubleshooting Procedure Related Information

Introduction
This document explains how to configure interVLAN routing with CiscoCatalyst 3750/3560/3550 series switches. The document provides a sample configuration for interVLAN routing with a Catalyst 3550 series switch that runs enhanced multilayer image (EMI) software in a typical network scenario. The document uses a Catalyst 2950 series switch and a Catalyst 2948G switch as Layer 2 (L2) closet switches that connect to the Catalyst 3550. The Catalyst 3550 configuration alsohas a default route for all traffic that goes to the Internet when the next hop points to a Cisco 7200VXR router. You can substitute a firewall or other routers for the Cisco 7200VXR router.

Prerequisites
Requirements
Ensure that you meet these requirements before you attempt this configuration: • Knowledge of how to create VLANs For more information, refer to Creating Ethernet VLANs onCatalyst Switches. • Knowledge of how to create VLAN trunks For more information, refer to the Configuring VLAN Trunks section of Configuring VLANs.

Components Used
The information in this document is based on these software and hardware versions: • Catalyst 3550−48 that runs Cisco IOS® Software Release 12.1(12c)EA1 EMI • Catalyst 2950G−48 that runs Cisco IOS Software Release 12.1(12c)EA1 EI •Catalyst 2948G that runs Catalyst OS (CatOS) version 6.3(10)

Note: The configuration from the Cisco 7200VXR is not relevant, so this document does not show the configuration. The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that youunderstand the potential impact of any command.

Related Products
This configuration can also be used with these hardware and software versions: • Any Catalyst 3750/3560/3550 switch that runs EMI software or standard multilayer image (SMI) Cisco IOS Software Release 12.1(11)EA1 and later • Any Catalyst 2900XL/3500XL/2950/3550 or CatOS switch model, used as the access layer switch

ConventionsRefer to Cisco Technical Tips Conventions for more information on document conventions.

Background Theory
In a switched network, VLANs separate devices into different collision domains and Layer 3 (L3) subnets. Devices within a VLAN can communicate with each other without the need for routing. Devices in separate VLANs require a routing device to communicate with one another. L2−only switchesrequire an L3 routing device. The device is either external to the switch or in another module on the same chassis. A new breed of switches incorporate routing capability within the switch. An example is the 3550. The switch receives a packet, determines that the packet belongs to another VLAN, and sends the packet to the appropriate port on the other VLAN. A typical network design segments thenetwork based on the group or function to which the device belongs. For example, the engineering VLAN only has devices that relate to the engineering department, and the finance VLAN only has devices that relate to finance. If you enable routing, the devices in each VLAN can talk to one another without the need for all the devices to be in the same broadcast domain. Such a VLAN design also has anadditional benefit. The design allows the administrator to restrict communication between VLANs with use of access lists. In the example in this document, you can use access lists to restrict the engineering VLAN from access to devices on the finance VLAN. The switch does not route non−IP packets between VLANs and routed ports. You can forward these non−IP packets with fallback bridging. In order...
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