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I'm almost confused about what the switch has really done with the voice traffic. I know access port traffic is always "untaged", but actually the "Switch port voice vlan (xxx)" command is used to send voice traffic as "dot1q" according to Cisco Official Docs Reffrence! (And it should usually be tagged, because of trunk characteristic)

So my question is should we consider one access port is both tagged and untaged traffic if we use voice vlan?! (but its against to expect tagged frame form acceess port i think)

And if not (The voice is also send as untaged), how the switch can determine its related traffic (voice, data)!?

For Better Understanding Let's Consdier: There is one switch, one PC, and One IP phone connected together:

SW (2960)---IPphone (7911)----PC
(The ip phone is placed between the switch "aceess port" and pc) - vlan 110: data, vlan111: voice

SW 2960 Config:

int fa 0/1
switch port mode access vlan 110
switchport access vlan 110
switchport voice vlan 111

The switch port for interface 0/1 is also show "access mode" but can we should expect any tagged traffic from access port if we use voice on the same access port? and does it global for non-cisco too?

Thanks in advanced

Ali Fanaei
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1 Answers1

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The Cisco switch and phone use CDP to facilitate the trunk negotiation. With a non-Cisco phone, you either configure a trunk interface, or the phone may be able to use LLDP to negotiate a trunk link.

A Cisco switch and phone will negotiate a trunk link on a switch interface configured as an access interface. A VoIP phone has an internal switch, and that internal switch negotiates a trunk link with the switch to which it connects, even if it connects on an access interface. That is what the switchport voice vlan switch configuration enables on your switch.

Ron Maupin
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