VoIP and Vlans - Need help understanding?

Posted on 2011-10-07
Last Modified: 2012-08-13
Can someone help me understand this:

My company will be getting a new VoIP phone system installed shortly and it is recommended we get our switches reconfigured to split Data and VoIP traffic using vlans.

That all makes sense to me, VoIP system broadcasts a lot of traffic etc.

My understanding of vlans was you use vlans to split ports on the switch.

eg: vlan 1(data) has 12 ports, vlan 2(voip) has 12 ports.

but that's 2 different networks, our users computers will be connected to the pass through port on the phone so PC to Phone to Network point.

I'm not asking how to configure a switch to do this. More so just asking for some information to help me understand what actually will be happening on my network.

Question by:antrimbc
    LVL 16

    Accepted Solution

    You'll use DHCP scope options for the phones so that they receive the correct VLAN information and IP address. Check with your VoIP equipment manufacturer to find out what scope options you'll need.

    LVL 7

    Assisted Solution

    As mqortega mentioned, you will need a dhcp scope for the phones.

    On you switch (and the way we do ours) is the ports your computers sit on will be untagged in the PC vlan, the same ports will be tagged to your voip vlan for the pass through devices. So yes, two different networks (vlans), but they can use the same ports.

    LVL 15

    Assisted Solution

    If you have a newer Cisco catalyst switch, it creates a quasi-Trunk between the switchport and the IP Phone.  The IP Phone actually has a little 3-port switch (one to the PC, one to the Phone, and one to connect to the switch).  You create the quasi-trunk by assigning an Access VLAN and a Voice VLAN to the port.   I believe on non-Cisco switches you actually have to create a trunk, but I have never dealt with that issue so I am not the best to ask.
    LVL 17

    Assisted Solution

    On a cisco you'll do the following:

    interface g0/1
      switchport mode access
      switchport access vlan 10
      switchport voice vlan 20

    vlan 10 is the data vlan which is sent without a tag natively.
    vlan 20 is the voice vlan which is sent with an 802.1q tag.

    on our 3com switches we create a trunk port which carry two vlans, the data vlan which is untagged and the voice vlan which is tagged.

    Author Closing Comment

    Thanks for the answers folks. I was thinking something similar but wasn't entirely sure. This has cleared it up.

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