Home > Articles > Cisco Network Technology > General Networking > Understanding and Configuring Multilayer Switching

Understanding and Configuring Multilayer Switching

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Jul 6, 2007.

Chapter Description

An understanding of multilayer switching is necessary for network designers, administrators, and operators for deployment and troubleshooting purposes. This chapter provides you with details, architecture, and methods of multilayer switching on Catalyst switches.

Configuration Exercise: Troubleshooting CEF-Based MLS

Complete this configuration exercise to familiarize yourself with the basic troubleshooting steps of CEF-based MLS.

Required Resources

The resources and equipment required to complete this exercise are as follows:

  • A Cisco IOS–based, Layer 3 CEF-based MLS Catalyst switch such as a Catalyst 3550, 3560, 3750, 4500, or 6500 with Supervisor II or 720 with an MSFC in a Layer 3 Building Distribution submodule or Layer 3 routing topology
  • A terminal server or workstation connected directly to the console port of the Catalyst switch

Exercise Objective

The purpose of this exercise is to demonstrate the first steps in troubleshooting CEF-based MLS on a Cisco IOS–based Catalyst switch. Troubleshooting CEF-based MLS is generally a last step in troubleshooting connectivity problems. Generally, connectivity problems are the result of a physical layer issue or configuration issue. Troubleshoot CEF-based MLS after all other troubleshooting steps have been exhausted.

Network Diagram

Figure 9-10 shows the network layout for this configuration exercise. The configuration exercise uses a Catalyst 3560 switch from the Building Distribution submodule to illustrate commands. This switch learns IP routing entries from the Campus Backbone switches.

Figure 9-10

Figure 9-10 Network Diagram for Configuration Exercise

Command List

In this configuration exercise, you use the commands listed in Table 9-4. These commands are in alphabetical order so that you can easily locate the information you need. Refer to this list if you need configuration command assistance during the exercise. The table includes only the specific parameters used in the example and not all the available options for the command.

Table 9-4. Command List for Configuration Exercise



ping ip_address

Sends ICMP echo requests to a specific IP address

show adjacency detail

Displays the CEF adjacency table and rewrite information

show ip arp ip-address

Displays the ARP table for a specific IP address

show ip cef destination-network detail

Displays the IP CEF FIB table for a specific destination network

show ip route destination-subnet

Displays the Cisco IOS IP routing table

Task 1: Establish Console (Out-of-Band) Connectivity or Telnet or SSH Connectivity to the Switch

This task is self-explanatory.

Task 2: Determine the IP Routing Entry or Subnet That Is Experiencing Connectivity Problems or a CEF-Based MLS Issue

For this configuration exercise, use the destination subnet,, as an example.

Task 3: Verify the Cisco IOS IP Routing Table and ARP Entries for the Route

Step 1

Verify that a route exists to the destination network in the IP routing table.

Switch#show ip route
Routing entry for
  Known via "ospf 3738", distance 110, metric 2, type intra area
  Last update from on Port-channel2, 05:59:50 ago
  Routing Descriptor Blocks:
  *, from, 05:59:50 ago, via Port-channel4
      Route metric is 2, traffic share count is 1, from, 05:59:50 ago, via Port-channel2
      Route metric is 2, traffic share count is 1

Step 2

Verify the ARP entries for the next-hop addresses for the destination subnet obtained in Step 1.

Switch#show ip arp
Protocol  Address          Age (min)  Hardware Addr   Type    Interface
Internet          1  00d0.03e5.840a  ARPA   Port-channel4

Switch#show ip arp
Protocol  Address          Age (min)  Hardware Addr   Type    Interface
Internet           1  00d0.03eb.b40a  ARPA   Port-channel2

Step 3

Using the ping command, send ICMP echoes to the next-hop address to verify connectivity.


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

Task 4: Verify the IP CEF FIB and Adjacency Entries for the Route

Step 1

Verify the IP CEF FIB entry for the destination subnet in question.

Switch#show ip cef detail, version 122, epoch 0, per-destination sharing
0 packets, 0 bytes
  via, Port-channel4, 0 dependencies
    traffic share 1
    next hop, Port-channel4
    valid adjacency
  via, Port-channel2, 0 dependencies
    traffic share 1
    next hop, Port-channel2
    valid adjacency
  0 packets, 0 bytes switched through the prefix

Step 2

Verify the CEF adjacency entry for the next-hop address obtained from Step 1, and compare the results to Step 2 in Task 3.

Switch#show adjacency detail | begin
IP       Port-channel4   
                                   0 packets, 0 bytes
                                   ARP        00:05:42
                                   Epoch: 0

Switch#show adjacency detail | begin
IP       Port-channel2   
                                   0 packets, 0 bytes
                                   ARP        00:04:53
                                   Epoch: 0

Task 5: Debug the CEF FIB and Adjacency Table's Downloads to the Centralized Switching and Distributed Switching Engines, and Verify the TCAM Contents for FIB and Adjacency Tables

This task should be performed only under the supervision of a Cisco TAC engineer.

7. Review Questions | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020