Voice VLANs question

Apologies if this is in the wrong section.
I may have a silly question about Voice VLANs or the question might be do I need it.

Is it possible to have the switch filter and separate traffic coming from a PC and IP Phone even if they are using the same line? Can I configure a switch to send traffic from the IP phone with higher urgency then the PC by using the MAC addresswa for both devices? If I do that I wouldn’t need a Voice VLAN or I wouldn’t need two VLANs at all and send them over the same VLAN?

Does this make since?

Hello Rafael

There is no such thing as a silly question. This is actually a very good question because it helps you to understand why things are made to function the way they do.

It is possible to have both voice and data travel on the same VLAN and to implement a class map that will match either source or destination MAC address. In this way, you would be able to provide for a QoS policy for packets destined to/coming from the MAC an IP telephone and not for packets to/from the connected PC.

However, QoS is not the only reason for separating voice and data traffic on a network. Arguably the most important is security. You wouldn’t want someone on the same VLAN to spoof your phone’s MAC address and have all voice traffic travel via the attackers PC where all packets are recorded and a conversation can be reconstructed. Also, at least for Cisco phones, DHCP would provide IP addresses as well as information about the TFTP server from which configuration files can be downloaded to the IP phones. It’s not prudent to have user PCs on this same subnet receiving the same DHCP information, albiet useless information for the PCs but very dangerous in the hands of attackers.

Although doable from a QoS standpoint, having IP phones and PCs in the same VLAN is not recommended especially for the purposes of security.

I hope this has been helpful!