Config Lab: Basic Port Security 4

Wendell Odom
By Wendell Odom October 5, 2021 15:05

The Cisco switch Port Security feature lets the switch monitor incoming frames, look at the source MAC address, and determine whether frames with that source address should or should not be allowed into the switch. As usual for these config labs, this one plays it straight, with straightforward requirements to configure. Details below the fold.

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

The Network, Initial State, and Rules

This lab uses the simple LAN shown in Figure 1. It shows two switches connected by a link, with a router on the side.

Figure 1 – Lab Topology

 

This lab begins with the router configured correctly but ignores the router configuration, focusing on the links between the PCs and the switches. However, for this exercise, the initial config has no real impact on configuring the switches for the new requirements.

Example 1: SW1 Initial Config

 

Example 2: SW2 Initial Config

 

For this lab:

  • The router has been configured already and is working.
  • The router is connected to other links, not shown; those links are entirely unimportant to the lab.
  • This lab uses only CCNA concepts, so the link between the two switches is not a VLAN trunk, and only the default VLAN (VLAN 1) is in use.

Now that you have the background, the rest of this post spells out your tasks.

 

Problem: Configure to Match the Requirements Table

This exercise does not match what you might do in real life because it asks you to do many different options in one small LAN. However, it does allow you to exercise the various command options. For this lab, configure the switch ports, so port security does the different combinations of features listed for each of the six PCs in the figure. That’s it!  The types of configuration settings include:

  1. The action (violation mode) the switch takes when a violation occurs: shutdown, protect, and restrict
  2. Whether the one PC’s MAC should be learned dynamically or statically configured
  3. Whether the switch should make a dynamically-learned MAC be “sticky” and remember it for later
  4. The maximum number of MACs that may be associated with the port.

The MAC addresses of the six PCs should be considered to be 8 hex zeros, with the last four digits matching the PC’s number. EG, PC1’s MAC is 0000.0000.1111; PC2’s is 0000.0000.2222, and so on.

PC1 PC2 PC3 PC4 PC5 PC6
Number of MACs 1 1 2 2 3 3
Dynamically learn MAC? Y N Y Y N Y
Sticky? N N Y N N Y
Violation mode Shut. Prot. Rest. Shut. Prot. Rest.

Table 1: Configuration Combinations

 

As a final requirement, you should configure only the required parameters. Do not configure any commands that could be picked up by default. That’s it! Jump in, and try a few.

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 listed in the lab exercise documentation versus those used in the sample CML file.

Device Lab Port  CML Port
SW1 F0/1 G2/1
SW1 F0/2 G2/2
SW1 F0/3 G2/3
SW1 F0/11 G1/1
SW2 F0/4 G3/1
SW2 F0/5 G3/2
SW2 F0/6 G3/3
SW2 F0/7 G0/1
SW2 F0/12 G1/2

Lab Answers Below: Spoiler Alert

Lab Answers: Configuration (Click Tab to Reveal)

Problem 1 Review, Switch SW1

To get things started, go back and check the original problem post for the details. For quick reference, Figure 1 repeats the topology, Table 1 repeats the requirements, and the notes just before the table list the MAC addresses.

Figure 1 – Lab Topology

MAC Addresses:

The MAC addresses of the six PCs should be considered to be 8 hex zeros, with the last four digits matching the PC’s number. EG, PC1’s MAC is 0000.0000.1111; PC2’s is 0000.0000.2222, and so on.

PC1 PC2 PC3 PC4 PC5 PC6
Number of MACs 1 1 2 2 3 3
Dynamically learn MAC? Y N Y Y N Y
Sticky? N N Y N N Y
Violation mode Shut. Prot. Rest. Shut. Prot. Rest.

Table 1: Configuration Combinations

Answers

The configurations for Problem 1 on both SW1 and SW2 are listed below.

Example 1: SW1 New Config

 

Example 2: SW2 Config

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

Cisco routers and switches allow a simple security method for both the console and for Telnet access. Basically, all you have to do is tell the device to use that method by supplying a prompt for the password (the login subcommand), and then define the password’s value (the password subcommand).

Note that the answer shows the configuration of the VTY password (to support Telnet) with VTYs 0 through 4 as separate from the configuration of VTYs 5 through 15. This quirk of Cisco output has to do with the fact that older IOS versions support only VTYs 0 through 4. You could have used the commands literally shown in the answer example, or you could have used the command line vty 0 15, followed by those same password and login commands.

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. After opening the supplied .pkt file, but before configuring any commands, test to see which PCs lease an IP address with DHCP:
    1. Use the ipconfig /all command from the PC command prompt to discover if the PCs have an IP address assigned from the DHCP server.
    2. As needed, use the ipconfig /release and ipconfig /renew commands to release the old address and attempt to renew a lease on an IP address.
  2. After configuring the lab:
    1. Repeat the above tests to confirm that all the PCs lease an address.
    2. From each PC, ping the other PC IP addresses. Because the lab begins with routing working, once DHCP works on each PC, the pings should all work as well.

More Labs with Related Content!

Config Lab: Basic Port Security 3
Config Lab: DHCP Relay
Wendell Odom
By Wendell Odom October 5, 2021 15:05
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