Configuring InterVLAN Routing with Catalyst 3550.pdf

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Cisco − Configuring InterVLAN Routing with Catalyst 3750/3560/3550 Series Switches
Table of Contents
Configuring InterVLAN Routing with Catalyst 3750/3560/3550 Series Switches........................................1
Document ID: 41260
................................................................................................................................1
Introduction..........................................................................................................................................................1
Prerequisites.........................................................................................................................................................1
Requirements..........................................................................................................................................1
Components Used...................................................................................................................................1
Related Products.....................................................................................................................................2
Conventions............................................................................................................................................2
Background Theory................................................................................................................................2
Configure.............................................................................................................................................................2
Network Diagram
....................................................................................................................................3
Configurations........................................................................................................................................4
Verify...................................................................................................................................................................9
Troubleshoot......................................................................................................................................................11
Troubleshooting Procedure...................................................................................................................11
NetPro Discussion Forums − Featured Conversations......................................................................................12
Related Information...........................................................................................................................................12
i
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
NetPro Discussion Forums − Featured Conversations
Related Information
Introduction
This document explains how to configure interVLAN routing with Cisco Catalyst 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 also has 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 on Catalyst 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
Cisco − Configuring InterVLAN Routing with Catalyst 3750/3560/3550 Series Switches
•
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 you understand 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
Conventions
Refer 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 switches require 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 the network 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 an additional 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.
Configure
In this section, you are presented with the information to configure the features described in this document.
Note:
Use the Command Lookup Tool
used in this document.
(
registered customers only
) to find more information on the commands
Cisco − Configuring InterVLAN Routing with Catalyst 3750/3560/3550 Series Switches
Network Diagram
This document uses this network setup:
In this diagram, a small sample network with the Catalyst 3550 provides interVLAN routing between the
various segments. By default, the Catalyst 3550 switch acts as an L2 device with disablement of IP routing. In
order to make the switch function as an L3 device and provide interVLAN routing, you must enable IP
routing globally.
These VLANs are the three VLANs that the user defines:
•
VLAN 2user VLAN
•
VLAN 3server VLAN
•
VLAN 10management VLAN
The default gateway configuration on each server and host device must be the VLAN interface IP address that
corresponds on the 3550. For example, for servers, the default gateway is 10.1.3.1. The access layer switches,
which are the Catalyst 2950 and 2948G, are trunked to the Catalyst 3550 switch.
The default route for the Catalyst 3550 points to the Cisco 7200VXR router. The Catalyst 3550 uses this
default route to route traffic destined for the Internet. Therefore, traffic for which the 3550 does not have a
routing table entry forwards to the 7200VXR for process.
Cisco − Configuring InterVLAN Routing with Catalyst 3750/3560/3550 Series Switches
Practical Tips
•
Separate the management VLAN from the user or server VLAN, as in this diagram. The management
VLAN is different from the user or server VLAN. With this separation, any broadcast/packet storm
that occurs in the user or server VLAN does not affect the management of switches.
•
Do not use VLAN 1 for management. All ports in Catalyst switches default to VLAN 1, and any
devices that connect to nonconfigured ports are in VLAN 1. The use of VLAN 1 for management can
cause potential issues for the management of switches, as the first tip explains.
•
Use an L3 (routed) port to connect to the default gateway port. In this example, you can easily replace
a Cisco 7200VXR router with a firewall that connects to the Internet gateway router.
•
Do
not
run a routing protocol between the Catalyst 3550 and the Internet gateway router. This
example configures a static default route on the 3550 instead. This setup is best if there is only one
route to the Internet. Make sure to configure static routes, preferably summarized, on the gateway
router (7200VXR) for subnets that can be reached by the Catalyst 3550. This step is very important
because this configuration does not use routing protocols.
•
If you have two Catalyst 3550 switches in your network, you can dual connect the access layer
switches to both 3550 switches. Run Hot Standby Router Protocol (HSRP) between the switches to
provide redundancy in the network. For more information on the configuration of HSRP, refer to the
Configuring HSRP
section of Configuring IP Services.
•
If you need additional bandwidth for the uplink ports, you can configure EtherChannel. EtherChannel
also provides link redundancy in the case of a link failure.
Configurations
This document uses these configurations:
•
Catalyst 3550
•
Catalyst 2950
•
Catalyst 2948G
Catalyst 3550 (Catalyst 3550−48 Switch)
Cat3550#show
running−config
Building configuration...
Current configuration : 3092 bytes
!
version 12.1
no service single−slot−reload−enable
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password−encryption
!
hostname Cat3550
!
!
ip subnet−zero
!−−− Enable IP routing for interVLAN routing.
ip routing
!!
!
spanning−tree extend system−id
!
!
Cisco − Configuring InterVLAN Routing with Catalyst 3750/3560/3550 Series Switches

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