Config Lab: CDP/LLDP 1

Wendell Odom
By Wendell Odom October 12, 2021 09:05

#CDP has long been the default and favored protocol for a variety of device discovery functions, but LLDP offers an alternative as well. (LLDP is new to the exam topics per the May 2016 new CCENT and CCNA R&S exams.) Both are supported in Cisco routers and switches, with similar configuration. This lab asks you to work through the commands to enable and disable both CDP and LLDP for the sake of exercising your CLI config skills with these protocols.

All about Config Labs

The blog has a series of lab exercises called “Config Labs.” Each lab presents a topology with the relevant initial configuration for each device. The lab also lists new requirements, after which you should create the additional configuration to meet those requirements. You can do the lab on paper, in a text editor, or use software tools like Cisco Packet Tracer or Cisco Modeling Labs.

Once you have created your answer, you can click various tabs at the bottom of this post to see the lab answers, comments about the lab, and other helpful information.

The Lab Exercise

Requirements

Configure CDP and LLDP in the topology shown in the figure. In particular, use CDP only in the top part of the topology, and LLDP only in the bottom part. The specific rules for this lab are:

  • Use only CDP on the R1 and R2 G0/2 interfaces
  • Use only LLDP on the R1 and R2 G0/1 interfaces
  • Use only CDP on switch SW1
  • Use only LLDP on switch SW2, R4, and R4
  • Assume all device interfaces shown in the lab are up and working

Figure 1: Device Discovery Topology

 

Initial Configuration

Examples 1 through 6 show the beginning configuration state of the four routers and the two switches.

Example 1: R1 Config

 

Example 2: R2 Config

 

Example 3: R3 Config

 

Example 4: R4 Config

 

Example 5: SW1 Config

 

Example 6: SW2 Config

Answer Options - Click Tabs to Reveal

You can learn a lot and strengthen real learning of the topics by creating the configuration – even without a router or switch CLI. In fact, these labs were originally built to be used solely as a paper exercise!

To answer, just think about the lab. Refer to your primary learning material for CCNA, your notes, and create the configuration on paper or in a text editor. Then check your answer versus the answer post, which is linked at the bottom of the lab, just above the comments section.

You can also implement the lab using the Cisco Packet Tracer network simulator. With this option, you use Cisco’s free Packet Tracer simulator. You open a file that begins with the initial configuration already loaded. Then you implement your configuration and test to determine if it met the requirements of the lab.

(Use this link for more information about Cisco Packet Tracer.)

Use this workflow to do the labs in Cisco Packet Tracer:

  1. Download the .pkt file linked below.
  2. Open the .pkt file, creating a working lab with the same topology and interfaces as the lab exercise.
  3. Add your planned configuration to the lab.
  4. Test the configuration using some of the suggestions below.

Download this lab’s Packet Tracer File

You can also implement the lab using Cisco Modeling Labs – Personal (CML-P). CML-P (or simply CML) replaced Cisco Virtual Internet Routing Lab (VIRL) software in 2020, in effect serving as VIRL Version 2.

If you prefer to use CML, use a similar workflow as you would use if using Cisco Packet Tracer, as follows:

  1. Download the CML file (filetype .yaml) linked below.
  2. Import the lab’s CML file into CML and then start the lab.
  3. Compare the lab topology and interface IDs to this lab, as they may differ (more detail below).
  4. Add your planned configuration to the lab.
  5. Test the configuration using some of the suggestions below.

Download this lab’s CML file!

 

Network Device Info:

This table lists the interfaces used in the lab exercise documentation that differ from those used in the sample CML file.

Device Lab Port  CML Port
SW2 G1/0/1 G0/1
SW2 G1/0/2 G0/2
SW2 G1/0/3 G0/3
SW2 G1/0/4 G1/0

Lab Answers Below: Spoiler Alert

Lab Answers: Configuration (Click Tab to Reveal)

Answers

Figure 1: Device Discovery Topology

Example 1: R1 Config

 

Example 2: R2 Config

 

Example 3: R3 Config

 

Example 4: R4 Config

 

Example 5: SW2 Config

Commentary, Issues, and Verification Tips (Click Tabs to Reveal)

Commentary

The default behavior of all Cisco devices is to have the Cisco Discovery Protocol (CDP) enabled on all interfaces. This behavior works well as long as the other deployed equipment in the network is either from Cisco or from a vendor that supports CDP. However, in cases where the connected device happens to use the standards-based Link Layer Discovery Protocol (LLDP), you need to disable CDP and enable LLDP.

For this lab, you were tasked with several configuration tasks that test your ability to configure different variations of CDP and LLDP; the specific order of the configuration is subjective.

On R1 and R2, the first task to configure is to enable LLDP globally with the lldp run global command. Then to run CDP only on some interfaces and LLDP only on other interfaces, you need to use some interface subcommands. Specifically, to disable CDP on their G0/1 interfaces, use the no cdp enable interface subcommand. LLDP uses a slightly different command; to disable LLDP on the R1 and R2 G0/2 interfaces, use both the no lldp transmit and no lldp receive interface subcommands.

For R3 and R4, because both use LLDP only, you can disable CDP completely and enable LLDP on all interfaces. First, to disable CDP globally, configure the no cdp run global command. Then, to enable LLDP globally, which automatically enables LLDP for both transmit and receive on all interfaces, configure the lldp run global command.

Next, consider the switches. Switch SW1 needs only default configuration, with CDP enabled globally, and LLDP disabled globally, so no new configuration is needed. Example 11 shows the configuration needed on switch SW2 to reverse those settings so that SW2 runs LLDP but not CDP.

Known Issues in this Lab

This section of each Config Lab Answers post hopes to help with those issues by listing any known issues with Packet Tracer related to this lab. In this case, the issues are:

# Summary Detail
1 None No known issues related to this lab.

 

Why Would Cisco Packet Tracer Have Issues?

(Note: The below text is the same in every Config Lab.)

Cisco Packet Tracer (CPT) simulates Cisco routers and switches. However, CPT does not run the same software that runs in real Cisco routers and switches. Instead, developers wrote CPT to predict the output a real router or switch would display given the same topology and configuration – but without performing all the same tasks, an actual device has to do. On a positive note, CPT requires far less CPU and RAM than a lab full of devices so that you can run CPT on your computer as an app. In addition, simulators like CPT help you learn about the Cisco router/switch user interface – the Command Line Interface (CLI) – without having to own real devices.

CPT can have issues compared to real devices because CPT does not run the same software as Cisco devices. CPT does not support all commands or parameters of a command. CPT may supply output from a command that differs in some ways from what an actual device would give. Those differences can be a problem for anyone learning networking technology because you may not have experience with that technology on real gear – so you may not notice the differences. So this section lists differences and issues that we have seen when using CPT to do this lab.

Beyond comparing your answers to this lab’s Answers post, you can test in Cisco Packet Tracer (CPT) or Cisco Modeling Labs (CML). In fact, you can and should explore the lab once configured. For this lab, once you have completed the configuration, try these verification steps. 

  1. Connect to any of the routers and display the LLDP and CDP neighbors. Use commands like show cdp neighbors, show lldp neighbors, show cdp interfaces, and show lldp interfaces. For instance, R1 should see SW1 as a neighbor with CDP and SW2 as a neighbor with LLDP. SW2 should see R1, R2, R3, and R4 as a neighbor with LLDP.

More Labs with Related Content!

Config Lab: DAI 1
Config Lab: NTP Client/Server
Wendell Odom
By Wendell Odom October 12, 2021 09:05
Write a comment

5 Comments

  1. Erik November 15, 15:35

    Hi,

    Just one typo in Example 6 SW2 Config: hostname SW1 global configuration command should reference “SW2”.

    Reply to this comment
  2. almeidajoaodealmeida November 20, 08:30

    Hi,
    I see that lldp was enabled globally, couldn’t it be possible to enable it per interface by using
    lldp receive
    lldp transmit, commands ?

    Reply to this comment
  3. almeidajoaodealmeida November 23, 04:20

    Hello Mr Odom,
    Just one typo on the last requirement, R4 was referenced twice.

    Reply to this comment
View comments

Write a comment

Comment; Identify w/ Social Media or Email

Subscribe

Subscribe to our mailing list and get interesting stuff and updates to your email inbox.

Thank you for subscribing.

Something went wrong.

Search

Categories