Trunking Puzzle 1

By certskills April 6, 2016 09:05

You can memorize VLAN trunking commands by staring at a table – but you will remember them much better if you try different combinations in sample labs, and especially if you try them from the CLI of some gear or simulator. This is a great lab to do on your gear for that reason. The lab: look at a few different contrived VLAN trunking requirements that are meant to make you exercise your memory of VLAN trunking configuration options, and then check the status to find out if the link is actually trunking.


Configure IEEE 802.1Q trunking between the devices shown in the figure. The specific rules for this lab are:

  • Configure SW1’s trunks so that they will actively attempt to form trunks with attached switches
  • Configure the trunk between SW2 and SW3 using manual trunking and disable DTP
  • Configure SW4’s trunks to use manual trunking
  • Assume all interfaces shown in the lab are up and working



Figure 1: Four Switches with Trunks

Initial Configuration

Example 1, 2, 3 and 4 show the beginning configuration state of SW1, SW2, SW3 and SW4.

Example 1: SW1 Config

Example 2: SW2 Config

Example 3: SW3 Config

Example 4: SW4 Config


Answer on Paper, or Maybe Test in Lab

Next, write your answer on paper. Or if you have some real gear or other tools, configure the lab using them.

To test your solution if you happen to try it with VIRL or real gear, you can check a few obvious items with show commands. First, each of the devices should now be successfully trunking on all interfaces connecting to the other switches; to verify this issue the show interfaces trunk command on each device. Note that you need to check the status on both ends of the link. Other useful commands include the show interfaces interface switchport command which will show a more detailed display of the encapsulation and mode that an interface is current using.

Do This Lab with Cisco’s VIRL

You can do these labs on paper and still get a lot out of the lab. As an extra help, we have added files for the Virtual Internet Routing Lab (VIRL) software as well. The .VIRL file found here is a file that when used with VIRL will load a lab topology similar to this lab’s topology, with the initial configuration shown in the lab as well.

Download this lab’s VIRL file!

The virl topology matches this lab topology exactly. The host info does as well.

Answers: IP Addresses 2
Answers: Trunking Puzzle 1
By certskills April 6, 2016 09:05
Write a comment


  1. Mike January 16, 13:19

    Should the lab read “disable VTP”?

    Reply to this comment
  2. Nick May 13, 05:59

    Mr Odom,
    I would like to thank you for your excellent certification book for the 100-105 exam.
    I took my test yesterday for the first time and passed with a 875. In preparation for the possibility of not passing, I took you advice and scribbled notes on the dry erase sheet they provided me, regarding questions that gave me trouble and tried to remember to jot them down after the test. When my passing score came up at the end of the exam, I was so excited that I handed in my dry erase sheet and forgot everything! It seems that for many of the subjects on the test, your book actually over prepared me. The only study tools I used were your book and PacketTracer.
    Thank you again.

    In reference to the one thing that I did remember, I experienced a situation where I needed to set up 802.1q trunking between two switches. To make a long story shorter(bet you were glad to hear that!), I had no idea that in order to issue one of the switchport mode trunking administrative mode options, the operational encapsulation mode must be 802.1q. Because your book references 2960’s, it was default and never an issue. Anyhow, I just thought that maybe in future versions, one of those little green boxes that start out with “Note” might indicate that if a switch is not set to a operational encapsulation mode of 802.1q, the commands for the switchport mode trunking administrative mode options won’t work. Command rejected: An interface whose trunk encapsulation is “Auto” can not be configured to “trunk” mode. I’m not sure if I should have been able to realize this from the chapter in the book. If I should have, I apologize. In any event, thanks again for a wonderful text and it’s time to buy your book for ICND2. One Final question, are the PDF and ePub versions of the book ever upgraded with respect to the errata or do they always reflect the final print version.

    Thanks again,

    Reply to this comment
  3. CCENTSkills May 16, 08:59

    Hi Nick,
    Thanks for the note. Glad you passed on the first try! Always a great relief to see that passing score.
    On the need to configure the trunking encapsulation, yes, the book ignores that fact, so you are correct that the book didn’t cover it. In practice, modern switches don’t require it, given that ISL is deprecated. However, I’ve noted that fact for the next edition, as you say, it’s worth a short note just in case.
    And on the eBooks and errata, they are supposed to be updated at the same time we update each new printing of the book. The process requires action on your part, and I do not know if it works if you buy the book for vendors other than directly from the publisher. But if you bought from the publisher, on the page where it lists your digital purchases, there’s an option to “refresh” the PDF, ePub, etc. Click that, and wait a few minutes. Then you can download the latest version with errata (and other typos) fixed.

    Reply to this comment
View comments

Write a comment

Comment; Identify w/ Social Media or Email


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

Thank you for subscribing.

Something went wrong.