Answers: Data and Voice VLAN 2

By certskills June 11, 2016 09:10

This latest lab takes a task that is relatively simple to learn and master and puts it into the context of a simple migration. The task: to migrate some switch access ports from connecting to PCs only, to instead connect directly to IP phones, which in turn connect to those same PCs. Read over the lab, create your own answer, and check my answers here.


Figure 1: Original Topology without IP Phones

Figure 2: New Topology with IP Phones


Example 1: Access1 Config


Example 2: Access2 Config



When working on a network that implements voice over IP, one of the common tasks to perform is to configure both a data and a voice VLAN on a single switch port. When configured in this way the switch port acts like a trunk and tags voice traffic with an 802.1q tag. The IP phone is connected in line with the PC and will strip this traffic away to itself and pass all untagged traffic to the PC. Since many different companies already have an existing data VLAN configuration it is a common project for an organization to alter this configuration to take advantage of the voice VLAN feature.

This lab tasks you with taking an existing configuration which utilizes data VLAN’s to connect to PCs and alter it to accommodate IP phones which are being added in-line with these PCs. Because each of the access switches was already configured to connect to the PCs the nice thing about the voice VLAN feature is the only thing that is required for configuration is the specific voice VLAN configuration. Since the interface range command was specified in the requirements, each access switch can be configured with these commands:

interface range GigabitEtherent1/0-3, followed by switchport voice vlan 30

interface range GigabitEthernet2/0-3, followed by switchport voice vlan 30

Data and Voice VLAN 2
RIPv2 Basics 2
By certskills June 11, 2016 09:10
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  1. adrikayak November 12, 15:29

    Errata: “802.11q tag”

    Reply to this comment
  2. MarceloVZ May 30, 01:00

    Hi. I have a question, I know that the ip phone tags voice traffic because of the vlan voice configuration but when you say: “The IP phone is connected in line with the PC and will strip this traffic away to itself and pass all untagged traffic to the PC”, I don’t understand. The PCs belong to data vlan (vlan 10 or 20), so the data traffic of the pc should be tagged too, a tag of data vlan 10 or data vlan 20. Or I’m confusing with the trunk link?

    Reply to this comment
    • CCENTSkills May 30, 16:16

      Admittedly, the terms and concepts are confusing. However, in normal operation on this sort-of-kind-of trunk:
      Traffic to/from the phone passes with 802.1Q header
      Traffic to/from the PC does not.

      There are other config options as well.

      But yes, if it were a normal trunk, and used a native VLAN of 1, then the traffic in both VLAN 10 and 20 would both cross the link with the 802.1Q header in the frames.
      Hope this helps,

      Reply to this comment
      • MarceloVZ May 31, 16:19

        And also (besides 10 and 20), in the normal trunk the VLAN 30 also cross the link with the tag, right?

        Your answer helped a lot. Thank you so much.

        Reply to this comment
        • CCENTSkills June 6, 09:40

          Sure thing! And yes, in a normal 802.1Q trunk, all frames that are part of a non-native VLAN include the 802.1Q header that lists the VLAN tag. That is, VLAN 30 frames would be tagged in this case.

          Reply to this comment
          • Michael August 30, 08:12

            Greetings to all! Mr. Odem, thank you very much for your books and especially extra materials, including this blog. I’ve tried a number of free online resources to learn and prepare for the CCNA, and I have always gotten stuck. I’m finally pushing through and understanding Routing and Switching once I began using your materials. Thank you!

            Question regarding trunking and 802.1q tagging: Do I understand the concept correctly, traffic between a switch and host (PC) through an access port is NEVER tagged. The switchport is in access mode, therefore no traffic has 802.1q tagging. In this example, Access1 and Access2 would receive tagged traffic from the other switches, but would remove the tags before forwarding out the appropriate access port.

            However, when adding a VoIP phone, the “switchport voice vlan [vlan ID]” command changes Access1 and Access2 switches’ behavior so that the link between the switch and phone becomes a trunk, forwarding 802.1q tagged traffic in the allowed vlan list (10 and 30 in Access1, 20 and 30 in Access2). The phone then strips the 802.1q headers for traffic being forwarded to the host (PC), sending them over what is essentially an access port from the phone to the PC.

            Am I understanding and explaining this properly?

  3. Fubr August 5, 19:09

    Hello Wendell

    Got a question I can’t wrap my head around with this question.
    Got the answer right because of the config. But on the switches I have been around the interfaces are consecutive (GigabitEthernet1/0, 1/1, 1/2…1/24) depending on if it is a 24 port or 48 port, Unless the switches are stack.

    Am I having a senior moment or are these access switches stack?

    Thanks for all your help to the community!!


    Reply to this comment
    • CCENTSkills September 7, 11:11

      Hi Fubr,
      The switches use the interface numbering of a VIRL IOSL2 image. VIRL is Cisco’s virtualization software you can purchase for about $200 per year. Then you get real Cisco software to run in VIRL. However, because LAN switches are so dependent on specific ASICs, VIRL comes with the more generic switch image called IOSL2. It’s the same image Cisco uses in the CCIE lab exams. Anyway, it uses a weird interface numbering scheme. So, when writing the lab, I could have used more normal-to-real-gear numbering, and not matched the VIRL config supplied with the lab, or matched the VIRL config (which I did), risking confusion in comparison to real switches! 🙂 But that’s why.

      Reply to this comment
  4. Drago September 21, 09:03

    Hey Wendell,

    I really appreciate, that you are providing feedback even after so long time since publishing the book.

    I have a maybe a little stupid question. Wouldnt we need to configure the switchport voice vlan 30 command also for distribution switches? Or for distribution level it does not matter ?

    Thank you in advance

    Reply to this comment
    • CCENTSkills September 25, 09:54

      Hi Drago,
      You’re welcome!
      Not a stupid question at all. The “switchport voice vlan 30” command is needed only on an access port connected to an IP phone, for the purpose of defining the VLAN used for the phone’s voice traffic. In addition, ALL switches (access and distribution included) must support that VLAN: they must have defined the VLAN (“vlan 30”) or learned of it with VTP, and the trunks must support VLAN 30.
      In this case, the distribution switches already had VLAN 30 defined, and the trunks did not remove VLAN 30 from their allowed lists, so the dist. switches should be ready for any VLAN 30 traffic.
      Hope this helps,

      Reply to this comment
  5. James December 12, 14:06

    Hello Wendell,

    Thanks for the great commentary! I am a bit confused in regards to the “interface range GigabitEtherent1/0-3” and “interface range GigabitEthernet2/0-3” command. Would these be the first and last ports on the access switch?

    Best Regards,
    James Watson

    Reply to this comment
    • CCENTSkills January 18, 10:21

      Hi James,
      Short answer is “no”. More meaningful answer:
      “interface range Gi1/0-3” means in this case: Gi1/0, Gi1/1, Gi1/2, Gi1/3. The lab topology was created to match the capabilities of VIRL, which uses an IOS switch image that’s NOT based on any particular Cisco switch model. It uses a different interface numbering scheme than the real switches you would see. I thought it’d be better to use topologies that could be replicated with VIRL rather than one that would require you to mentally map the lab to your tool VIRL, PT, etc).
      The other command references interfaces Gi2/0, 2/1, 2/2, 2/3.
      Hope this helps,

      Reply to this comment
  6. Stefano B. August 26, 14:55

    Hi Wendell, I wonder if interface range g1/0-3, 2/0-3 is fine. If yes, can we remove the space between “,” and “2” resulting in interface range g1/0-3,2/0-3?

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