IP Telephony and VLAN's - Necessary?

This has been bugging the crap out of me as of late and I was hoping someone here could possibly shed some light on it for me...

As is common with IP phones now, they generally have a switchport on the back for you to plug your PC into. From all the research I've done, it seems to be recommended that you place your phones into their own separate VLAN.

This is accomplished by creating a type of trunk link between the switch and phone, allowing the link to pass traffic for both the PC and phone.

Now...here's what I'm struggling with. How does placing the phones in their own VLAN "protect" anything when broadcasts sent from any PC will still hit the phone first, then the PC?

Let's also assume that your voice traffic already has QoS applied on each switch automatically, without the use of VLAN's.

I suppose I'm having trouble realizing where the real benefit of VLAN's comes into play in this particular scenario. If the PC's and phones were not connected together and each device had it's own dedicated switchport, then I could understand, as the phones would never see any traffic but their own.

Anyone have thoughts on this?

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Comments

networker050184

/usr wrote: »

If the PC's and phones were not connected together and each device had it's own dedicated switchport, then I could understand, as the phones would never see any traffic but their own.

That is exactly what the internal phone switch does. It is a small three port switch that send PC traffic to the PC and phone traffic to the phone. The phone isn't going to see any broadcast from the data VLAN.