topic Re: What does the voice option for VLAN in the CLI do? in Switches, Hubs, and Modems

What does the voice option for VLAN in the CLI do?

Jig_2 — Fri, 20 Oct 2006 18:58:37 GMT

Hi all.

I recently purchased a procurve 2824 (which I love) and I have 2 VLANs, the default for data and another for VoIP phones.

I noticed in the CLI there is a "voice" option, ie: vlan 2 voice.

What exactly does "voice" do? Does it automatically prioritize certian packets?

Thanks!

Re: What does the voice option for VLAN in the CLI do?

Matt Hobbs — Fri, 20 Oct 2006 20:01:32 GMT

That's a good question. With the switches that support LLDP-MED, (2600, 5300) the voice VLAN setting is required so that the VoIP phone can detect which is the 'voice' VLAN.

On the 2800 which does not support LLDP-MED (not sure if it will in the future) then the voice VLAN as far as I know really does nothing special at all.

Re: What does the voice option for VLAN in the CLI do?

Jig_2 — Mon, 23 Oct 2006 12:34:12 GMT

Hi Matt!

So since the phones are already in a vlan, should i do a QoS based off the VLAN ID or the DSCP field?

I once tried setting vlan 2 with a priority of 7 and that totally choked our data b/w. Thanks.

Re: What does the voice option for VLAN in the CLI do?

Matt Hobbs — Mon, 23 Oct 2006 18:12:38 GMT

For the 2800 you may want to try enabling the 'qos-passthrough-mode'. This will change the switch from 4 queues to 2, but will definitely help in achieving line rate transfers - especially if you are using any 100Mbit devices on the switch.

Once you have that enabled, you should be able to enable the VLAN ID priority like you have (I usually set 6 but 7 should be the same).

If you continue to see poor data performance after doing this it would seem to me that the voice VLAN is using more bandwidth than what would be expected. Does the port utilisation seem fairly low or not?

Depending on your network topology, (i.e, you need your voice traffic to go over a WAN) I wouldn't worry too much about DSCP.