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Voice Vlans

Hi, I would really appreciate some advice on how to go about setting up QoS across a network.

For the purposes of QoS and security would I be right in assuming the best method to set up QoS would be to assign different voice vlans for different areas of the network?

For example say I had 15 departments and they were seperated into 15 different access vlans for PC's, would it be best to set up 15 new voice vlans, one for each department or is it ok to just set up one voice vlan?

Am I also correct is assuming that using the voice vlan will then give an automatic CoS value to IP phone traffic of 5 (and 3 for call set up) and then 0 for all other normal PC traffic?

Many thanks in advance for you help.


Re: Voice Vlans


The reasoning that led you to create 15 VLANs for your departments would probably also lead you to use the same setup for your voice vlans. However, there is no reason why it would not work with just a single voice vlan.

By default, Cisco IP phones will reset all traffic from the PC to a CoS/DSCP of 0. And also, they will send voice traffic with CoS=5 and DSCP=EF. However, that by itself is not sufficient to give it priority within the network. You need to configure your access ports to trust the traffic from the attached IP phones. A good way of configuring this is to use AutoQos for VoIP which will do a lot of the configuration for you.

Hope that helps - pls rate the post if it does.


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