How can I keep network traffic to a minimum with this scenario?

Posted on 2009-02-18
Last Modified: 2012-05-06
I have been asked to help an existing client set up a VOIP phone network. We have purchased GB POE Switches to support this. I had been planning to set up a VLAN to keep data traffic off the VOIP network and reduce latency, but today, I discovered that the cabling contractor has only run one cable drop to each desktop. They planned to plug the drop cable into the VOIP phone and then run another cable from the phone to the desktop computer. Does anyone have any suggestions on how to do this since now both VOIP packets and data packets will need to co-exist on each switch port?
Question by:ClydeB
    LVL 3

    Accepted Solution

    I am assuming that the switches are Cisco or equivalent. Based on this, you would set both a access vlan and voice vlan on the port. This can be accomplished on Cisco switches by using the following example configuration.
    switchport mode access
    switchport access vlan 100
    switchport voice vlan  200
    no shut
    The phone in essence creates a trunk with the switch allowing only the two VLANs. The voice vlan may need to be set on the phones as well either through DHCP or manual configuration.

    Author Comment

    Since reading your post, I have done some research and now understand the basic concept, I think.
    1. My current data network is on 192.168.50.x,, with a gateway of This would be the default VLAN; in other words, untagged. All eqpt on the data network would be in this subnet.
    2. The phones, which are on the same drop as the computers, would be assigned to a different subnet; e.g., 192.168.60.x., and all of the phones would be sending VLAN tags for VLAN 200. I would set this up, as you described, on each port, and on the port that is going to the Mitel 5000, I would ONLY allow VLAN tags with a value of 200. This would block computer traffic from reaching the phone switch.
    3. But, the phone switch needs to be accessible from the internet using port forwarding of several ports. I guess that doesn't require anything special.
    4. What would I specify for my gateway for VLAN 200? And how would I route traffic between the 2 subnets if I wanted to?

    LVL 3

    Expert Comment

    The gateway could be a VLAN interface on the switch, a router interface connected to the subnet, a firewall interface attached to the subnet or whatever the design calls for. What does the access vlan use as it's gateway? In answer to your other question, depending on the switch or gateway, you can just turn routing on. 3560's, 3750's, 4948's ect... are all layer 3 switches capable of routing. The voice VLAN is no different than the access VLAN. It can be set as the access VLAN for any device you want, it is only a logical separation over a physical medium.

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