1. InterVLAN Routing Chapter 6
Purpose: This module overviews multilayer switching and describes how to configure this feature on both Cisco switches and routers.
Timing: The total amount of time to complete this chapter:
Lesson—3 hours
Laboratory Exercises —1 hour
Note: This section has a laboratory exercise at the end.
Contents: This section includes the following topics:
Objectives
Defining multilayer switching
Hardware and software requirements
The components of multilayer switching
How multilayer switching works
Commands that disable multilayer switching
Laboratory Exercise
Summary
Review
Transition: Following are the list of performance objectives that describe what students will be able to do at the end of the course.

2. Objectives
Upon completion of this chapter, you will be able to perform the following tasks:
Identify the network devices required to effect interVLAN routing
Configure a default gateway to ensure network reachability
Configure a route processor to facilitate interVLAN routing
Purpose: This slide states the module objectives.
Timing: The total amount of time to complete this chapter:
Lesson—40-45 minutes
Laboratory Exercises —1 hour
Note: This section has a laboratory exercise at the end.
Emphasize:
Read or state each objective so each student has a clear understanding of the module objectives.
Transition: Following is a signpost of the chapter topics.

3. InterVLAN Routing In this chapter, we discuss the following topics:
InterVLAN routing issues
Distribution layer topology
Configuring interVLAN routing
Purpose: This slide discusses what major topic areas are discussed in this chapter.
Emphasize:
Read or state each topic area so each student has a clear understanding what will be covered in the chapter.
At the end of this module, the students will be able to:
Transition: Following is a signpost of the topics covered in the first section “InterVLAN Routing Issues”

4. InterVLAN Routing In this section we discuss the following topics:
InterVLAN Routing Issues
Isolated Collision Domains
Finding the Route
Supporting Multiple VLAN traffic
Distribution Layer Topology
Configuring InterVLAN Routing
Purpose: This slide signposts the topics covered in this section
Emphasize:
Read or state each topic so each student has a clear understanding of what is covered in this section
Transition: Following is a definition of a multilayer switching.

5. Problem: Isolated Broadcast Domains
VLAN10
VLAN20
VLAN30
Purpose: This slide poses the problem of communicating between VLANs.
Emphasize:
Point out that VLANs, by their nature, are designed to keep data from traversing the VLAN borders.
However, end users stations need to communicate with entities outside the VLAN borders.
Use the example of end users in one VLAN needed to communicate with enterprise servers residing in a VLAN across the network core.
Transition: Following introduces the solution.
Because of their nature, VLANs inhibit communication between VLANs

6. Solution: Routing Between VLANs
VLAN10
VLAN20
VLAN30
Purpose: This slide introduces routers as the solution to InterVLAN communications.
Emphasize:
In switched networks, route processors are used to provide communications between VLANs.
Before you can configure routing between VLANs, you must have defined the VLANs on the switches in your network.
Refer to the Cisco Internetworking Design Guide and appropriate switch documentation for information on these topics.
The Cisco Internetworking Design Guide is available from Cisco Press.
InterVLAN Routing is discussed in the Cisco IOS Switching Services Configuration Guide located on the Cisco Documentation CD-ROM.
Transition: Following begins the discussion of some problems that occur as result of InterVLAN routing.
Communications between VLANs require a routing processor

7. Problem: Finding the Route
I need to send this packet to That
address is not on my
local segment.
VLAN10
VLAN20
Purpose: This slide introduces the problem of how to resolve routes between VLANs.
Emphasize:
Some network devices use routing tables to identify where to deliver packets outside of the local network segment.
Even though it is not the responsibility of end user devices to route data, these devices still must be able to send data to addresses on subnets other than their own.
Transition: Following begins the discussion of some problems that occur as result of InterVLAN routing.
Network
Network
InterVLAN communications introduce the problem of where end-user stations send nonlocal packets

8. Solution: Defining a Default Gateway
I will send the packet to
my default router.
VLAN10
VLAN20
Network
Network
Purpose: This slide discusses the solution of default gateways.
Emphasize:
IP hosts tend to be configured with a default gateway or configured to use Proxy ARP in order to find a router on their LAN.
Convincing an IP host to change its router usually required manual intervention to clear the ARP cache or to change the default gateway.
Transition: Following is a discussion of how multiple sources use a single router to communicate with a single source.
I know where
network
is!
End-user stations send nonlocal packets to a default router

9. Problem: Supporting Multiple VLAN Traffic
I need information
from File Server A.
I need information
from File Server A.
I need information
from File Server A.
I have three distinct streams of traffic destined for the same place! ? ? ? ?
Purpose: This slide discusses the solution of multiple links to a single router.
Emphasize:
Transition: Following is a discussion of multiple links to single router.
File Server A
VLAN10
VLAN20
VLAN30
Multiple VLANs interfacing with a single route processor require multiple connections or VLAN trunking

10. Solution: Multiple Links
VLAN10
VLAN20
VLAN30
VLAN60
Purpose: This slide discusses the solution of an ISL link from multiple VLANs to a single router.
Emphasize:
Point out that multiple links may work in a small installation.
However, as the number of VLANs per switch increases, so does the requirement for the number of interfaces on the route processor.
Some VLANs may not require interVLAN routing on a regular basis, creating a situation where interfaces on the route processor are infrequently or under-utilized.
Transition: Following is a discussion of ISL links to single router.
The router can support a separate interface for each VLAN

11. Solution: Inter-Switch Link
VLAN10
VLAN20
VLAN30
VLAN60
Eth 3/0.1
3/0.2
3/0.3
Purpose: This slide discusses the solution of ISL.
Emphasize:
The Inter-Switch Link (ISL) protocol is used to inter-connect two VLAN-capable Fast Ethernet devices, such as the Catalyst 5000 or Cisco 7500 routers. The ISL protocol is a packet-tagging protocol that contains a standard Ethernet frame and the VLAN information associated with that frame.
ISL is currently supported over Fast Ethernet links, but a single ISL link, or trunk, can carry traffic from multiple VLANs.
The concept of ISL was discussed in the “Defining Common Workgroups” chapter. How to configure ISL links is discussed later in this chapter.
Discuss the example in the SG.
Transition: Following is a discussion of ISL links to single router.
Eth 3/1.1
3/1.2
3/1.3
The router can support a single ISL link for multiple VLANs

12. InterVLAN Routing In this section we discuss the following topics:
InterVLAN Routing Fundamentals
Distribution Switch Topology
External Route Processors
Internal Route Processors
Configuring InterVLAN Routing
Purpose: This slide states the module objectives.
Emphasize:
Read or state each objective so each student has a clear understanding of the module objectives.
Transition: Following is a discussion on the topology at the distribution layer.

13. Distribution Layer Route Processors
Purpose: This slide discusses the distribution layer.
Emphasize:
Point out that the distribution layer consists of a combination of high-end switches and route processors.
The distribution layer is the demarcation between networks in the access layer and networks in the core.
Transition: Following is a discussion of an external topology.
Distribution Layer
The distribution-layer device is a combination of a high-end switch and a route processor

14. External Route Processor
VLAN41
Network
VLAN41
Network
Switch A
Switch B
Switch C
VLAN42
Network
Purpose: This slide discusses the external router topology.
Emphasize:
Point out that the student can use existing Cisco high-end routers in conjunction with the Netflow Feature Card (NFFC) or NFFCII on a Catalyst family switch to implement multilayer switching.
The router must be directly attached to the Catalyst switch either by multiple Ethernet connections (1 per subnet) or by a Fast Ethernet connection using an Inter-Switch Link (ISL).
The Cisco high-end routers supporting multilayer switching include the Cisco 7500, 7200, 4500, and 4700 series routers. These routers must have the MultiLayer Switch Protocol (MLSP) software and IOS or later software installed to provide the Layer 3 services to the switch.
Work through the example in the student guide.
Transition: Following is a discussion of an internal topology.
An external Cisco high-end router and a Catalyst 5000 switch with an NFFC or NFFCII
Connected by multiple Ethernet connections or an ISL link

15. Internal Route Processors
VLAN41
Network
VLAN41
Network
VLAN42
Network
Purpose: This page discusses the external router topology.
Emphasize:
Cisco multilayer switch can be a Catalyst 5000 series switch equipped with a Cisco System Route Switch Module (RSM), or Route Switch Feature Card (RSFC).
The multilayer switch can also be a Catalyst 6000/6500 series with a Multilayer Switch Module (MSM).
The RSM or MSM is a router module running normal Cisco IOS router software. This router module plugs directly into the Catalyst series switch backplane.
Note: The Catalyst series switch must contain at least 3 slots to house the Supervisor III module, the RSM, and a line card. Any other requirements, such as redundant supervisor engines or multiple line cards, would require a larger chassis.
This course focuses on the RSM as this is the equipment used in the laboratory exercises. The command set for the RSM is identical with the 6000/6500 series.
Transition: The following continues the discussion of the internal router
Multilayer switches integrate Layer 2 and Layer 3 functionality in a single box

16. Internal Route Processors (cont.)
RSFC
RSFC is a daughter card on the Supervisor Engine IIG and IIIG
Purpose: This page discusses the internal route processor.
Emphasize:
The RSM resides in slots Slot 1 is reserved for the supervisor engine. Slot 2 may be used for a backup/redundant supervisor engine.
Slot 13 is reserved for an ATM or 8510 module.
The maximum number of RSM modules for the Catalyst 5500 switch is seven. However, this number may be reduced depending on the number of ATM modules present. You can use any combination of ATM and RSM modules as long as the total does not exceed seven
The RSM interface to the Catalyst 5000 series switch backplane is through VLAN0 and VLAN1. VLAN 0 is mapped to channel 0 and VLAN 1 is mapped to channel 1. VLAN 0 is used for communication between the RSM and the Catalyst 5000 series switch and is not accessible to the user.
VLAN 1 is the Catalyst 5000 series switch default VLAN. Additional VLANs are toggled between the two channels as they are created.
Transition: The following is the signpost for the next section.
RSM
RSM can reside in slots 2 through 12 of a Catalyst 5000 switch

17. InterVLAN Routing In this section we discuss the following topics:
InterVLAN Routing Fundamentals
Distribution Layer Topology
Configuring InterVLAN Routing
Locating and accessing the route processor
Configuring an interface
Defining a default gateway
Testing the link
Purpose: This slide states the section topics.
Emphasize:
Read or state each topic so each student has a clear understanding of the what is discussed in the next section
Transition: Following discusses how to locate the route processor.

18. Locating the Route Processor
Switch (enable) show module
Mod Module-Name Ports Module-Type Model Serial-Num Status
Supervisor III WS-X ok
/100BaseTX Ethernet WS-X5225R ok
Route Switch WS-X ok
Purpose: This slide gives the command to display the modules in the switch.
Emphasize:
The Catalyst 5000, 4000, 2926G, or 2926 series switches are multi-module systems.
The show module command displays what modules are installed, as well as the MAC address ranges and version numbers for each module.
Entering the show module command without specifying a module number displays information on all modules installed in the system.
Specifying a particular module number displays information on that specific module.
In this example, point out the route switch module is in slot 3.
This example does not show the complete display due to space constraints on the slide. Point out the SG example shows the complete display.
Transition: Following describes how to access the route processor module.
Specifying a particular module number displays information on that module
Not specifying a module number displays information on all modules installed in the system

19. Accessing the Route Processor
Switch (enable) session 3
Purpose: This slide gives the command to connect to the route processor module from the switch prompt.
Emphasize:
Use the session command to access the RSM from the switch prompt. The command requires you designate the module number.
The module number is obtained by issuing the show module command on the switch.
Once the session command executes, you are logged onto the route processor.
At this point, you are in user EXEC command mode on the route processor and you have direct access only to the RSM with which you have established a session.
The RSM supports only one session command at a time.
To exit from the router CLI back to the switch CLI, enter the exit command at the Router> prompt.
Transition: Following describes how to uniquely identify each router.
Eliminates the need to connect a terminal directly to the RSM console port

20. Identifying the Route Processor
Router(config)#hostname RSM143
Router(config)exit
RSM143#
Purpose: This slide describes the command to uniquely identify the RSM.
Emphasis:
Naming your router helps to better manage the network by being able to uniquely identify each route processor within the network.
The name of the route processor is considered to be the host name and is the name displayed at the system prompt.
To clear the hostname, enter the no hostname command in global configuration mode.
Do not expect case to be preserved. Upper- and lowercase characters look the same to many internet software applications. For more information, refer to RFC 1178, Choosing a Name for Your Computer. The name must also follow the rules for ARPANET host names. They must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphens. Names must be 63 characters or fewer. For more information, refer to RFC 1035, Domain Names--Implementation and Specification.
Transition: The following describes how to enable a routing protocol.
The hostname uniquely identifies each route processor within the network

21. Enabling an IP Routing Protocol
RSM141(config)#ip routing
RSM141(config)#router igrp 1
RSM141(config-router)#network
Network
Purpose: This slide describes the ip routing and network commands.
Emphasis:
Routing protocols determine optimal paths through internetworks using routing algorithms, and transport information across these paths.
Point out the Advanced Cisco Router Configuration (ACRC) course discusses network routing and routing protocols in greater detail.
The ip routing command assigns a routing protocol to a route processor
The network command informs the routing protocol which interfaces will participate in the send and receiving of routing updates.
The network number must identify a network to which the router is physically connected.
Transition: Following begins the discussion of mapping VLANs to interfaces.
Routing protocols determine optimal paths through the network and transport information across these paths

22. Configuring an VLAN Interface on an Internal Route Processor
RTR144(config)#interface vlan41
RTR144(config-if)#ip address
RTR144(config-if)#exit
RTR144(config)#interface vlan42
RTR144(config-if)#ip address
Purpose: This slide describes creating a VLAN on an internal route processor.
Emphasis:
Configuring interVLAN routing on the RSM consists of two main procedures:
Creating and configuring VLANs on the switch and assigning VLAN membership to switch ports.
Creating and configuring VLAN interfaces for interVLAN routing on the RSM.
A VLAN interface must be configured for each VLAN between which traffic is to be routed.
VLANs are created at the switch level to group ports into virtual LANs. VLANs are controlled at the route processor level.
Each VLAN that the RSM is routing appears as a separate virtual interface. The RSM has one global MAC address that applies to all interfaces on that device.
When interfacing with a Catalyst 1900 switch, uniquely specify a MAC address for each RSM interface. The Catalyst 1900 switch does not store a direct VLAN/MAC address mapping in the CAM table. If you configure multiple links to the same RSM, problems can occur in the 1900 switch. For example, the Catalyst 1900 has two links to a single RSM. Because only one MAC address is designated for each VLAN, the Catalyst 1900 will record the last port data was sent out on in the CAM table and Spanning Tree will block the other link. However, if that link is an active link and data is sent out the second link, then the switch will update the CAM table and STP will block the first link, even though both links are valid.
Transition: Following discusses configuring an external route processor interface.
The internal route processor automatically encapsulates packets using ISL
Initial configuration requires a no shutdown command

23. Configuring an VLAN Interface on an External Route Processor
Port
Slot
Subinterface Number
RSM144(config)#interface fastethernet 0/1.1
RSM144(config-if)#encapsulation isl 10
RSM144(config-if)#ip address
RSM144(config-if)#exit
RSM144(config)#interface fastethernet 0/1.2
RSM144(config-if)#encapsulation isl 20
RSM144(config-if)#ip address
Encapsulation Type and VLAN Number
Interface FA 0/1
Subinterface 0/1.1
VLAN10
Purpose: This slide describes the commands to configure a multiple VLAN interface on an external route processor.
Emphasis:
On an external router, an interface can be logically divided into multiple, virtual subinterfaces.
Subinterfaces provide a flexible solution for routing multiple data streams through a single physical interface.
To accomplish this goal, you need to customize the subinterface to create the environment in which the subinterface is used.
To define subinterfaces on a physical interface, perform the following tasks.
Identify the interface
Define the VLAN encapsulation
Assign an IP address to the interface
Transition: The following describes how to define a default gateway.
VLAN20
Interface FA 0/1
Subinterface 0/1.2
Subinterfaces allow for routing multiple data streams through a single physical interface
Initial configuration requires a no shutdown command

24. Defining a Default Gateway
ASW31#config t
Enter configuration commands, one per line. End with CNTL/Z
ASW31(config)#ip default-gateway
Default Gateway
VLAN40
VLAN30
Purpose: This slide describes the command to define a default gateway.
Emphasis:
In order to forward a datagram, the sending device must first know what routers are connected to the local network and which route processor maintains the shortest path to the destination devise.
A default gateway is used to forward all non-local packets.
Discuss the commands to configure a default gateway on both the IOS and Set command-based systems.
You can add several routes to the switch, including the default route. This does not make the switch a router, nor does this command effect the switching of IP packets through the switch. This command is solely for IP communications to the switch, not for data through the switch.
Transition: The following describes how to remove an interface from a null domain.
Default Gateway
ASW41#config t
Enter configuration commands, one per line. End with CNTL/Z
ASW41(config)#ip default-gateway
Defining a default gateway facilitates interVLAN communications

25. Testing the Link The ping command tests connectivity to remote hosts
Purpose: This slide discusses the ping command.
Emphasize: Use the ping command to test connectivity to remote hosts.
The ping command will return one of the following responses:
Success rate is 100 percent or ip address is alive. This response occurs in 1 to 10 seconds, depending on network traffic and the number of ICMP packets sent.
Destination does not respond. No answer message is returned if the host does not
Unknown host. This response occurs if the targeted host does not exit
Destination unreachable. This response occurs if the default gateway cannot reach the specified network
Network or host unreachable. This response occurs if there is no entry in the route table for the host or network.
You can also test the routes packets will take from the route processor to a specific destination by using the trace ip destination command.
For more information on the trace ip command, refer to the Cisco IOS Release 12.0 Command Summary .
Transition: Following is the visual for the laboratory exercise.
PC41#ping
Sending 5, 100-byte ICMP Echos to , time out is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max 0/0/0/ ms
The ping command tests connectivity to remote hosts

26. Laboratory Exercise: Visual Objective
Switch Block X
VLAN x1
VLAN x2
VLAN x3
VLAN x4
Purpose: This slide overview what the students will build in class.
Emphasis:
Point out that the students will configure their distribution layer route processors.
At the end of this lab, the students will be able to ping end user station not residing in their own VLANs.
Transition: Following is the laboratory exercise.

27. Network Diagram

28. Summary
InterVlan routing is a requirement to enable communication between devices in separate VLANs.
Most devices are configured with the IP address of a default router to which all non-local network packets are sent.
The Inter-Switch Link (ISL) protocol is used to facilitate multiple VLAN traffic over a single link.
The distribution layer routing processor can be an internal or external router/switch topology.
Purpose: This page summarize what was discussed in this module
Transition: The following are the review questions.

29. Review
List at least two problems that can impede communications between VLANs, and identify a solution for each problem.
Identify at least two Cisco platform solutions for an internal route processor topology at the distribution layer.
Compare and contrast the steps used to configure an interface on an RSM and an ISL link on an external router.
Purpose: This page provides several topics for discussion
Emphasize:
Points of discussion for review question 1:
VLANs are associated with individual networks or subnetworks; therefore, network devices in different VLANs cannot communicate with one another.
Because VLANs isolate traffic to a defined collision domain or subnet, network devices in different VLANs cannot communicate with one another without some intervening device to forward packets between subnets.
In switched networks, route processors are used to provide communications between VLANs. Route processors provide VLAN access to shared resources and connect to other parts of the network that are either logically segmented with the more traditional subnet approach or require access to remote sites across wide- area links.
Connecting the separate subnets through a route processor introduces the issue of how end user devices can communicate with other devices through multiple LAN segments.
So that each end device does not have to manage its own routing tables, most devices are configured with the IP address of a designated route processor. This designated route processor is the default router to which all non-local network packets are sent.

30. Review (text only) Points of discussion for review question 2:
Any one of the following solutions are viable:
A Catalyst 5000 with an RSM
A Catalyst 5000 with an RSFC
A Catalyst 6000 with an MSM
A Catalyst 6500
Points of discussion for review question 3:
For an internal route processor:
Enter the VLAN number as part of the interface command.
Assign a unique Ip address to that interface.
Administratively enable the interface.
For an external route processor:
Identify the interface type and subinterface number.
Define the VLAN encapsulation type and VLAN number
Assign an IP address to the interface
Administratively enable the interface