I've got a customer using some Netgear switches for their small network and the phones don't seem to consistently be on one VLAN or another. It looks like what it's doing is inspecting the MAC on traffic, matching against an OUI list, and pushing the traffic to the voice VLAN. The phones are totally unaware that the voice VLAN exists, and they retain the values I push from my server for marking DSCP on SIP, RTP, and SRTP, and I see the switch learning the MAC in both VLANs.
If we change the configuration such that the phone learns the VLAN from LLDP, the phones revert all the DSCP settings to 0 for each instead of 26/46/46.
I replicated this on a TPLink switch I have at home both ways. At the very least my switch works consistently, where his sometimes works the first way and sometimes the second way. I referred him to Netgear support since it's not my switch and I'm not spending a lot of time fussing with it.
I am in the office today about to fire up an Extreme 210 and Cisco 4948 switch to see if they do the same thing when having the phone learn the voice VLAN via LLDP.
Is this normal behavior? I couldn't find anything on my switch at home for informing the phone of what DSCP values to use, only how to do mappings from dot1p to DSCP. Since we daisy chain phones, it seems like untrusting the port and marking traffic on the switch wouldn't be the way to go since if I understand right, that would mark traffic from the PC too.
His actual problem on site is very intermittent one way audio, and unless the switch is failing to work one way or the other mid way through calls I'm not thinking this is his actual problem anyway. More something I've noticed and something I'm asking for help understanding, more than happy to do reading if anyone has some links or books to point me towards too. For context I'm the HPBX vendor.
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